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The official blog of ornithology journals The Auk and The Condor
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Darwin’s Finches – Where Did They Actually Come From?

Tue, 05/15/2018 - 12:20

Española cactus finch (geospiza conirostris) Photo credit: S Taylor

In 1835, Charles Darwin visited the Galapagos Islands and discovered a group of birds that would shape his groundbreaking theory of natural selection. Darwin’s Finches are now well-known as a textbook example of animal evolution. But just where did a species synonymous with the discovery of evolution come from? A new study from The Auk: Ornithological Advances presents some of the best models to date on where these birds actually originated.

San Diego State University’s Erik Funk and Kevin Burns set out to determine the ancestral biogeography – how a species’ distribution varies over space and time – of Coerebinae. Coerebinae is a subfamily of birds called tanagers. This group includes the famous Darwin’s Finches and their fourteen closest relatives. Using state-of-the-art statistical software, Funk and Burns modeled two competing hypotheses. Both hypothesis models contained the same geographic area of the Galapagos, South America, and the Caribbean, but one model divided this area into more subregions than the other. The subregions were based on areas that shared similar plants and animals, such as the the Amazon or the Andes. When eight subregions were included in the model, the results indicated that the Caribbean, not the closer South American mainland, was more likely to be the origin of this bird group. However, the opposing model contains only five regions and indicates that the South American mainland is as likely as the Caribbean to be the home to Darwin’s Finches’ ancestors. The authors conclude that the current data suggest both potential origin sites are equally likely. Funk says, “the results…were a bit surprising, because they suggested a dispersal pattern that was not necessarily the most ‘straightforward’ explanation for how these birds arrived in the Galápagos. I think one of the big take-away messages here is the possibility that biogeographic events, like dispersal, may not necessarily happen like logic tells us they should. Darwin’s finches are such a highly studied group, and it is often taken for granted they arrived from mainland South America, but hopefully our results show readers that there is no more support for this hypothesis than there is for a Caribbean origin.”

Funk and Burns suggested the successful colonization of the Galapagos Islands was a result of two traits. First, the finches’ ancestors were more likely to wander than other species and consequently encountered islands more often. Second, these ancestors had a large amount of genetic variation in bill size and shape. This diversity in bill morphology allowed them to establish themselves and exploit their newfound niche. Better understanding the biogeography of Darwin’s Finches allows scientists to learn how animals move, and how this affects their subsequent evolution and ability to adapt to new or changing environments.

“In 2018, we still have fundamental things to learn about one of the most studied and celebrated groups of birds, Darwin’s Finches. Perhaps we should be calling them Darwin’s Tanagers because it is Burns’ tree of life for these birds, nesting them firmly in Tanagers, that is enabling new insights into the evolution, morphology, and origins of this remarkable group of birds. Funk and Burns use new biogeographic techniques in conjunction with recent phylogenies to explore the origins of Darwin’s Finches,” adds Shannon Hackett, Associate Curator in the Department of Zoology, and Head of the Field Museum’s Bird Division at the Field Museum, who is an avian diversity and phylogeny expert who was not involved in the research.

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Biogeographic origins of Darwin’s finches (Thraupidae: Coerebinae) will be available May 9, 2018, at http://www.americanornithologypubs.org/doi/full/10.1642/AUK-17-215.1

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology that began in 1884 as the official publication of the American Ornithologists’ Union, which merged with the Cooper Ornithological Society in 2016 to become the American Ornithological Society. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

Wintering Warblers Choose Agriculture Over Forest

Tue, 05/08/2018 - 13:15

Yellow Warbler Photo credit: S Valdez

Effective conservation for long-distance migrants requires knowing what’s going on with them year-round—not just when they’re in North America during the breeding season. A new study from The Condor: Ornithological Applications uncovers Yellow Warblers’ surprising habitat preferences in their winter home in Mexico and raises questions about what their use of agricultural habitat could mean for their future.

Large areas of natural forest in the Mexican lowlands have been converted to agriculture, and without enough habitat to go around, researchers speculate that the biggest, oldest birds might claim the choicest spots. To find out, Simon Fraser University’s Simón Valdez-Juárez and his colleagues studied Yellow Warblers wintering in western Mexico, counting how many birds were using each of three different types of habitat—riparian gallery forest, scrub mangrove forest, and agricultural land—as well as capturing birds to determine their age, sex, size, and likely point of origin. To their surprise, they found the highest density of warblers in agricultural habitat rather than either type of natural forest. There was also little evidence that a bird’s body size, sex, or age influenced where it ended up, although females’ habitat use differed depending on where they had spent the breeding season.

Irrigated agriculture may be attractive to Yellow Warblers as an alternative to the naturally dry forest habitat, which becomes even drier as winter goes on, or the limited availability of natural land cover may force most birds to occupy agricultural areas. Either way, this preference for agriculture could lead to problems if stressors such as pesticide use reduce the birds’ survival. “The implications for migratory bird populations depend on whether the condition and survival of birds wintering in agriculture is lower than that of birds wintering in natural habitats or not,” says Valdez-Juárez. “If it is lower, it might cause localized declines, as females from the contiguous U.S. and western Alaska were more likely to use agricultural habitats and lower female survival has been implicated in the population declines of other warblers.”

“With increasing agricultural intensification across the ranges of many long-distance migratory songbirds, it is critical to determine if they are using these new habitats. This new study shows that yellow warblers overwintering in western Mexico not only use agriculturally dominated habitats but are more common there than nearby sites with more natural landcover,” adds University of Manitoba Assistant Professor Kevin Fraser, an avian behavior and conservation expert who was not involved in this research. “They also report that more southern breeding females are more likely to use agricultural habitats than more northern breeding females, suggesting any impacts of overwintering habitat use may differ by breeding latitude. These results are important, as they highlight the need to investigate whether regions undergoing agricultural intensification are providing viable habitat for overwintering migrants, and how their use may carry-over to impact survival or fecundity in subsequent seasons.”

Use of natural and anthropogenic land cover by wintering Yellow Warblers: The influence of sex and breeding origin will be available May 2, 2018, at http://www.bioone.org/doi/full/10.1650/CONDOR-17-180.1 (issue URL http://www.bioone.org/toc/cond/120/2).

About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology. It began in 1899 as the journal of the Cooper Ornithological Club, a group of ornithologists in California that became the Cooper Ornithological Society, which merged with the American Ornithologists’ Union in 2016 to become the American Ornithological Society. In 2016, The Condor had the number one impact factor among 24 ornithology journals.

Where do birds molt their feathers? New research indicates molting grounds are discrete from breeding and wintering sites.

Mon, 05/07/2018 - 09:09

Nashville Warbler, one of 140 species whose post-breeding movements to molting areas were examined in a new study by The Institute for Bird Populations. Results indicate that Nashville Warblers in western North America disperse upslope from breeding areas to molt, whereas in the East, they move downslope and south. Many such east-west differences within species were found, reflecting differing climate and insect availability across North America. This photo was taken in August, when Nashvilles are on their molting grounds. (Photo by Frank D. Lospalluto via Flickr Creative Commons).

A new study by The Institute for Bird Populations finds that many North American birds do not molt on their breeding territories, as previously thought, but disperse or migrate in late summer to discrete molting locations before continuing their migration to wintering areas. The locations and habitats at these molting sites — and their conservation status — remain largely unknown.

Effective conservation of migratory birds depends on the protection of habitats used during all phases of their life cycle. New research by The Institute for Bird Populations, a non-profit bird conservation organization, has shed light on a key phase of the annual cycle: where birds go to molt after they breed. The study was published May 2, 2018 in the journal The Auk: Ornithological Advances.

Molt is an energetically taxing process during which birds shed worn or broken feathers and grow new ones. During this time, a bird’s flight ability is reduced, so they become harder to find than at other times of year. “Molt has been under-studied by ornithologists. Birds become very retiring at this time, as if on vacation, to recover from the breeding season,” said Peter Pyle, lead author on the study. Despite its importance to a bird’s survival, the subject has received a lot less attention than other factors such as breeding, migration, and wintering habitats. “We still have no clue where most North American landbirds undertake their post-breeding (prebasic) molt, and we need more information on the particular habitats or foods that are most important, and the conservation status of these areas.”

The new study relied on 17 years of records from The Institute for Bird Populations’ Monitoring Avian Productivity and Survivorship (MAPS) Program, a continent-wide bird banding effort assisted by thousands of citizen scientists and professional biologists. Data from more than 760,000 capture records of 140 species of landbirds collected at 936 MAPS bird-banding stations across North America were used to generate the results. The authors leveraged this extensive data set to estimate what proportion of birds known to breed at a station were also captured molting there, and vice versa. Dashed lines indicate delineation of western and eastern North America.

Although some bird species are known to undergo “molt-migrations” — movement to a molting location that is neither where they nested nor where they will winter — to take advantage of wetter conditions or more abundant food in areas such as the Sierra Nevada mountains in California or the late summer monsoonal rain area in the desert Southwest, most species have been assumed to molt on or near their breeding territories. This turns out not to be the case.

The study demonstrated some surprising findings, including widespread evidence of molt-migration for many species previously thought to molt only on their breeding grounds. The researchers analyzed spatial differences between breeding and molting locations, and found evidence that, across North America, birds shifted in nearly every compass direction, and with some going higher in elevation and some lower to find suitable molting areas. “In some cases this may be hundreds of kilometers away, in others it may be down the block,” Pyle noted.

Most of the 140 species examined (indicated by 4 letter codes abbreviating their common names) showed movements from breeding to molting areas. Species lower/further left on each graph show a lower probability of being recaptured during molt at a site where it bred. In the graph, species names in orange were known to molt away from breeding grounds, those in blue were thought to molt on breeding territories, and those in black are residents, presumed to molt on or near breeding territories. The new study largely validates these results for species marked in orange and black, but many species previously presumed to molt on breeding grounds (those in blue) appear to undergo molt migrations.

Although western North American species and populations have previously been reported to undergo more molt-migration than eastern species, this study found similar evidence of molt-movement between the two regions, although many species in the west migrate longer distances.

Two examples of molt migration movements by North American birds. Bluer areas represent higher probability of a bird breeding relative to molting at that site and redder areas represent higher probability of molting relative to breeding. As with Nashville Warbler (see above), Orange-crowned Warblers in the West moved significantly further south and higher in elevation, largely into the Sierra Nevada mountains of California, likely to take advantage of cooler and moister habitats at these locations in late summer. Within the MAPS area, Swainson’s Thrushes in the East appeared to shift west and south, largely into the Mississippi Valley, but did not appear to shift elevations.

These findings have significant implications for conserving birds. Although molting areas appear to be crucial for completing a species’ annual life cycle, more study is needed to determine if such areas are receiving the conservation attention or protection they need. The new research also indicates that individuals within a species make various molt-movement choices, even on an annual basis, in response to breeding season success or environmental and food conditions each year. “Rather than characterizing molt as occurring on discrete breeding or wintering grounds, it can perhaps best be thought of as a process occurring along a continuum, with most some species, populations, or individuals showing some level of movement from breeding territories to molt,” said Jim Saracco, another author on the study. “Our findings highlight the need for better understanding of molt-movement patterns and habitat needs during molt to better inform full life-cycle conservation strategies.”

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Evidence of widespread movements from breeding to molting grounds by North American landbirds is available at http://www.bioone.org/doi/full/10.1642/AUK-17-201.1 For more information about this study, contact Peter Pyle (ppyle@birdpop.org).

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology that began in 1884 as the official publication of the American Ornithologists’ Union, which merged with the Cooper Ornithological Society in 2016 to become the American Ornithological Society. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

Is the Rufous Hummingbird a Mexican monsoonal molt migrant?

Fri, 05/04/2018 - 11:58

Rufous Hummingbird, Photo credit: T Hopwood

Many species of North American hummingbirds are highly migratory, with some traveling over 2,000 km. These migratory birds risk more feather wear due increased solar exposure on an annual basis compared to non-migratory species. Hummingbirds, like all birds, need their feathers to be in good condition to survive and therefore have to undergo molt.

All North American migratory hummingbirds undergo complete molts on wintering grounds in Mexico before they migrate north. In first-year birds, this complete molt has been referred to as the performative molt and in all subsequent years, it is called the definitive prebasic molt. First-year males were also known to replace some throat feathers during the fall, replaced again during the complete overwinter molt.

However, a recent study by Dittmann and Cardiff suggested that molting in migratory hummingbirds may be more complex than simply the annual molt (2009, Birding 41: 32–35). They examined molt of Ruby-throated Hummingbirds during their fall migration from June to September on the Gulf Coast of Louisiana and found evidence of molting at this time in both adults and young. They called this molt an inserted molt, separate from the overwinter complete molt.

Curious whether inserted molts might occur in other migratory hummingbird species, we examined molt in the Rufous Hummingbird, a Mexican species that migrates to the northern United States and Canada to breed. We examined 346 specimens of Rufous Hummingbirds from three different specimen collections in California. We looked at each specimen for signs of molt in four feather regions: the crown, the back, the throat (including the gorget in adult males), and the underparts. We considered a bird as showing evidence of molt if we found any replaced feathers contrasting with worn feathers, indicating two generations of feathers in a single region, or if we found pin feathers present in any of the regions.

As expected, the majority of the specimens collected in the winter from southern Mexico showed signs of the complete molt that was known to take place on the wintering grounds. However, we also found signs of molting in both young birds and adults during southbound migration in the fall. These inserted molts occurred in all four feather regions but were more limited in extent than those of Ruby-throated Hummingbirds. Many (but not all) molting specimens were collected in the Mexican monsoonal region of northwestern Mexico. The Sierra Madre Occidental, a mountain range that lies within the monsoonal region attracts Rufous Hummingbirds because of the high flower abundance that occurs there, and we infer that the hummingbirds take advantage of this food resource to molt in this area, as do many western North American species of passerines.

Surprisingly, we found that the inserted throat feather molt in Rufous Hummingbirds varied greatly among ages and sexes. Adult males showed no evidence that their iridescent throat feathers were replaced in fall, whereas some adult females and all young birds of both sexes replaced at least some throat feathers during the inserted molt. New iridescent throat feathers might give young birds an advantage when defending territories by showing dominance. While it is still unclear why the highly migratory Ruby-throated and Rufous Hummingbirds undergo inserted fall molts in other body regions, one reason could be that their feathers become more worn compared to non-migratory hummingbirds.

We compared molts of Rufous Hummingbirds to the molts of basal Apodiform taxa, including Vaux’s Swift and Rivoli’s Hummingbird. We propose a terminology that would consider the inserted molts as the definitive prealternate molt in adults and the preformative molt in young birds. Therefore, we propose that Rufous Hummingbirds undergo a prealternate and preformative molt migration to the Mexican monsoonal region.

Our work on Rufous Hummingbirds is part of The Institute for Bird Populations’ Avian Molt Research Program, aimed at understanding molt strategies of all species of birds, standardizing molt and plumage terminologies worldwide, and applying findings to age-related demographic studies, habitat requirements for molt, and, ultimately, the conservation of birds.

~Post written by authors: Desmond Sieburth and Peter Pyle

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Evidence for a prealternate molt-migration in the Rufous Hummingbird and its implications for the evolution of molts in Apodiformes is available, at http://www.bioone.org/doi/full/10.1642/AUK-17-231.1 (issue URL http://www.bioone.org/toc/tauk/135/3).

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology that began in 1884 as the official publication of the American Ornithologists’ Union, which merged with the Cooper Ornithological Society in 2016 to become the American Ornithological Society. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

Rethinking the Umbrella Species Concept

Wed, 05/02/2018 - 16:54

Brewer’s Sparrow’s nest. Photo credit: J Carlisle

According to the “umbrella species” concept, preserving and managing habitat for a single high-profile species also benefits a whole suite of other species that share its habitat—but how well does this really work? Not all species that share the same general habitat necessarily have the same specific needs, and a new study from The Condor: Ornithological Applications finds that habitat management to benefit Greater-Sage Grouse in Wyoming can actually harm some of its songbird neighbors.

Shrub mowing is sometimes done to benefit sage-grouse during their chick-rearing season, when they favor habitat with fewer shrubs and more grass and forbs. The University of Wyoming’s Jason Carlisle (now at Western EcoSystems Technology) and his colleagues collected data on the abundance and nesting success of three songbird species before and after shrub mowing in central Wyoming, as well as at un-mowed sites for comparison. Two of the species, Brewer’s Sparrows and Sage Thrashers, are “sagebrush obligates” that rely heavily on shrub habitat. The researchers found no Brewer’s Sparrow or Sage Thrasher nests in mowed patches, where it may be decades until shrubs have regrown enough to be used for nesting, and the mowing treatment also reduced the overall abundance of Sage Thrashers by around 50%. Vesper Sparrows, on the other hand, are more flexible in their habitat use and were actually more abundant in patches where mowing was most extensive.

“The umbrella species concept is an appealing shortcut,” says Carlisle. “However, when conservation practitioners go beyond protecting the umbrella species’ habitat and start manipulating habitat conditions to meet the needs of the umbrella species, they risk harm to other species that also rely on those areas.” The mowed area in the study was only about five square kilometers, and cost and logistics make in unlikely that this treatment will be implemented on a large scale, so the negative effects of these habitat manipulations are likely more than offset by the positive effects of broader-scale sage-grouse conservation efforts. Still, Carlisle and his colleagues suggest that more monitoring is needed in general of how non-target species fare under umbrella-species management.

“It is clear that the observed effects on ‘background’ species are not consistent across the range of potential beneficiaries, and that the assumed benefits do not accrue to many,” adds Russel Norvell, an Avian Conservation Program Coordinator at the Utah Division of Wildlife Resources, who was not involved with this research. “It is likely these effects will persist, given the relatively slow growth rates in this arid system. While the conservation of Greater Sage-Grouse habitats across its range is likely to encompass much good, local habitat manipulations driven by unexamined assumptions or uninformed by landscape context have much to prove.”

Nontarget effects on songbirds from habitat manipulation for Greater Sage-Grouse: Implications for the umbrella species concept is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-200.1 (issue URL http://www.bioone.org/toc/cond/120/2).

About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology. It began in 1899 as the journal of the Cooper Ornithological Club, a group of ornithologists in California that became the Cooper Ornithological Society, which merged with the American Ornithologists’ Union in 2016 to become the American Ornithological Society. In 2016, The Condor had the number one impact factor among 24 ornithology journals.

Endangered Petrels and Trawl Fishing Clash in Tasman Sea

Mon, 04/30/2018 - 13:16

Photo Credit: T Poupart

Today’s shifting environmental conditions are creating an uncertain future for many top predators in marine ecosystems, but to protect the key habitat of a species, you first have to know where that habitat is and what threats might be affecting it. A new study from The Condor: Ornithological Applications looks at where New Zealand’s endangered Westland Petrel forages during its breeding season and shows that its range overlaps more with trawl fishing activity than conservationists realized.

The Museum of New Zealand Te Papa Tongarewa’s Susan Waugh and her colleagues outfitted 73 petrels with GPS loggers over the course of four breeding seasons to track where they went during their foraging trips in the Tasman Sea. The results show that the birds’ core feeding areas were consistent from year to year, located within 250 kilometers of their breeding colonies and focused on highly productive areas where the seafloor is steeply sloped. These sites often overlap with areas of significant trawl fishing activity, and further data is needed to see whether this co-occurrence translates into bird mortality. The species is the tenth most at-risk species from the impacts of New Zealand commercial fishing, but it appears that its actual ranking may be even higher as a result of the finding that the species is exposed to more fisheries activity than was previously understood.

“Our work on Westland petrels started in 2010, with a desire to understand how this species was faring demographically, as well as the key influences on it,” says Waugh. “Our work highlights a key factor in the birds’ ecology that has strong implications for conservation—these birds predictably use the same waters year in and year out, regardless of El Niño cycles, and they are therefore a great candidate for a marine protected area to create protection of their trophic relationships. We feel this Westland Petrel foraging data will provide a high-quality information source to help define key areas for marine conservation that will also provide protection for a whole suite of species.”

“A remarkable and important aspect of this study is that they performed this investigation during a six-year period, encompassing a variety of environmental conditions. Whatever the sex or the breeding stage considered, Westland Petrels consistently foraged in the same core areas from year to year,” adds Christophe Barbraud of the French National Centre for Scientific Research, a seabird conservation expert who was not involved in the study. “Since these areas were also consistently and heavily used by trawl fisheries, these results call for the implementation of marine spatial management tools, such as marine reserves or restrictions and monitoring of interactions between individual Westland Petrels and trawl fisheries, to ensure the conservation of this endangered petrel species.”

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Environmental factors and fisheries influence the foraging patterns of a subtropical seabird, the Westland Petrel (Procellaria westlandica), in the Tasman Sea is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-179.1 (issue URL http://www.bioone.org/toc/cond/120/2).

About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology. It began in 1899 as the journal of the Cooper Ornithological Club, a group of ornithologists in California that became the Cooper Ornithological Society, which merged with the American Ornithologists’ Union in 2016 to become the American Ornithological Society. In 2016, The Condor had the number one impact factor among 24 ornithology journals.

Will increasingly frequent warm-water events in the Gulf of California reduce seabird populations? The case of Heerman’s Gull

Fri, 04/27/2018 - 17:35

Photo Credit: Enriqueta Velarde

[Video link: https://vimeo.com/260369044/7cacabb12e%5D

Oceanic warm-water events in the Gulf of California have increased in frequency during the last three decades, passing from a historic mean of one or two warm anomalies per decade to five events in the 2007–2016 period. This can lead to massive failures in seabird nesting, as anomalously warm waters accumulate in the ocean’s surface, preventing the upwelling of colder, nutrient-rich waters from the ocean bottom, which in turn deprives seabirds of their food.

A recent study by Enriqueta Velarde from the University of Veracruz and Exequiel Ezcurra from the University of California Riverside, published in The Condor: Ornithological Applications, analyzed four decades of nesting dynamics of the threatened Heermann’s Gull (Larus heermanni), and modeled population growth under normal and high sea-surface temperature conditions.

Heermann’s Gulls exhibit the main characteristics of seabirds.  They can live for decades, but take many years to reach breeding age, and produce few young.  These traits allow their populations to resist oceanographic anomalies of up to one event every five years, but population size may decline rapidly if the frequency of warm-phase anomalies is over two per decade.  Under normal conditions, predicted population growth is around 4%, with production of fledglings contributing to the population increase. Under anomalous warm-water conditions, population growth drops to -15% and adult survival becomes the key condition for the survival of the species. Simulations project a rapid population decline if warm anomalies maintain the high frequencies they have shown during the last decade.

These results underscore the need to understand the dynamics of warming ocean waters under current large-scale environmental change, as well as the importance of following the demographic dynamics of seabirds as indicators of oceanic conditions. Monitoring seabird populations may provide us with warning signals about the health and the future of our marine ecosystems.

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Are seabirds’ life history traits maladaptive under present oceanographic variability? The case of Heermann’s Gull (Larus heermanni) is available at http://americanornithologypubs.org/doi/full/10.1650/CONDOR-17-5.1

About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology. It began in 1899 as the journal of the Cooper Ornithological Club, a group of ornithologists in California that became the Cooper Ornithological Society, which merged with the American Ornithologists’ Union in 2016 to become the American Ornithological Society. In 2016, The Condor had the number one impact factor among 24 ornithology journals.

Feather replacement or parental care? Migratory birds desert their offspring to molt

Thu, 04/26/2018 - 10:12

This is a male Hooded Warbler delivering food to his three 6-day-old nestlings. When replacing their tail feathers during molt, many males desert their nestlings and fledglings, leaving the female responsible for all remaining parental care. Photo Credit: Ron Mumme

A new study shows that when feather replacement and parental care overlap in time, migratory songbirds make a striking trade-off; they desert their offspring, leaving their mates to provide all remaining parental care.

This radical solution to conflict between parental care and the annual molt provides “a nice illustration of the complex lives that migratory songbirds lead,” says Ron Mumme, the study’s author and Professor of Biology at Allegheny College in northwestern Pennsylvania. “They have to negotiate conflicting demands and make difficult trade-offs and compromises, just like we do.”

Migratory songbirds that breed in North America confront serious issues with time management. After spending a relatively leisurely winter and early spring luxuriating in warm tropical climates, they migrate north for a brief but highly eventful summer in North America, during which they must complete three energetically demanding and time-consuming tasks: (1) they must build nests, lay eggs, and provide for their offspring until the young reach independence, (2) they must completely replace all the feathers in their plumage as part of the annual molt, and (3) they must prepare for the fall southward migration by eating prodigiously and storing the body fat that will fuel their long-distance flights.

Completing all three tasks during a short summer is challenging; when the tasks overlap in time, migratory songbirds may be forced to make compromises and trade-offs.

The new study, published in The Auk: Ornithological Advances, a journal of the American Ornithological Society, examines the trade-offs that birds make when parental care overlaps with the annual molt. It focuses on the Hooded Warbler, a songbird that spends a brief summer nesting in the forests of eastern North America before migrating south to winter along the Caribbean coast from southern Mexico to Panama.

Hooded Warblers have an unusual combination of traits that makes conflicts between parental care and molt likely. First, their prolonged nesting season extends into August, a time typically reserved for feather replacement. Second, their diet consists largely of flying insects that are captured in an unusual way; they use their white tail spots and tail-flicking behavior to flush prey hidden in vegetation. Third, the birds employ the odd strategy of molting and replacing all their tail feathers simultaneously at a time when they are also replacing the primary flight feathers on each wing.

Hooded Warblers simultaneously engaged in both parental care and tail molt therefore find themselves in a difficult position; they have to find enough food to feed themselves and their offspring at a time when their own nutritional requirements are high and their ability to fly and forage is significantly compromised.

So what happens when a molting Hooded Warbler loses all its tail feathers while it is still feeding nestlings or fledglings? About 70% of the time it deserts, leaving its mate responsible for all remaining parental care.

“For that one week when they are without a tail, Hooded Warblers are the goofiest looking birds you can imagine,” says Mumme. “But the big problem is flying and foraging are just not easy during that time. Molting birds typically hunker down in thickets and keep a low profile, and that usually isn’t compatible with parental care.”

Males arrive on the breeding grounds earlier than females and nearly always begin molt earlier than their mates. As a result, most cases of desertion involve molting males deserting nestlings and recently fledged juveniles, but rare cases of single-parent desertion by molting females also occur.

One intriguing aspect of the study is that it identifies two factors that explain why some molting parents do not desert; age of the dependent offspring, and age of the parent. If the offspring are older and close to the age of independence, which occurs about 35 days after hatching, a tailless molting parent may continue providing care. If the offspring are younger and more demanding, however, a molting parent nearly always deserts. Similarly, old veteran males are less likely to desert than are younger males with fewer years of previous breeding experience. These observations indicate that Hooded Warblers are acutely sensitive to the costs of providing parental care during molt. “If the costs of continuing care are relatively modest — for example, if it’s an experienced male with offspring close to independence,” says Mumme, “a molting parent may elect not to desert.”

A second intriguing finding is that females deserted by males and forced to provide all remaining parental themselves appear to have about the same chance of surviving to the following year as non-deserted females. In fact, in cases where both a deserting male and his mate return the following year, the female will more likely than not re-mate with the same male that ditched her the previous year. “Male desertion doesn’t seem to be a big problem for females,” says Mumme. “It may just be an unavoidable consequence of the prolonged nesting season and early male molt, and females are able to deal with it just fine.”

Mumme’s research on molt and desertion is continuing. He is currently investigating the effects of single-parent desertion on growth and survival of offspring, and how females adjust their molt and migration schedules to deal with male desertion.

The trade-off between molt and parental care in Hooded Warblers: Simultaneous rectrix molt and uniparental desertion of late-season young  is available at http://www.bioone.org/doi/10.1642/AUK-17-240.1

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology that began in 1884 as the official publication of the American Ornithologists’ Union, which merged with the Cooper Ornithological Society in 2016 to become the American Ornithological Society. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

After a Volcano Erupts, Bird Colonies Recover

Wed, 04/25/2018 - 11:06

Photo Credit: G Drew

Where do seabirds go when their nesting colony is buried by a volcano? In 2008, the eruption of the Kasatochi volcano in the Aleutian archipelago provided a rare opportunity to track how the island’s Crested and Least auklet populations responded when their nesting colony was abruptly destroyed. As a new study from The Auk: Ornithological Advances shows, the birds were surprisingly adaptable, establishing a new colony on freshly created habitat nearby in only four years.

Crested and Least auklets rely on habitat that must be maintained by continual disturbance—they nest in crevices in talus slopes formed by rock falls, which eventually become unusable when they’re filled in with soil and debris. The volcano’s 2008 eruption buried all of the suitable nesting habitat for the 100,000 Crested Auklets and 150,000 Least Auklets that had been nesting on Kasatochi.

The U.S. Geological Survey’s Gary Drew and his colleagues surveyed the island and its bird community by boat twice prior to the eruption and five times in the first eight years afterward, as well as deploying time lapse cameras at two locations on Kasatochi to monitor the auklets’ activity. Eleven months after the eruption, birds were sitting on the thick layer of ash covering their former nesting site, with no sign of any successful nests; the number of auklets turning up at the site declined each year. However, in 2012, Drew and his colleagues found a new auklet colony at a recently formed talus field north of the original colony site. Surveys of birds at sea indicated that some may also have moved to another nearby island.

“We were surprised at the speed at which the auklets were able to shift and make use of the new colony site. These birds typically nest in very large colonies, so there may be a tipping point where newly available habitat shifts rapidly from being a site of no or low density nesting to a site of high density nesting,” says Drew. “Fortunately, both Crested and Least auklets are currently doing well and we do not have any immediate concerns regarding the status of these two species. That said, these findings provide us a potential template for predicting the trajectory of auklet populations in response to habitat loss and interpreting auklet behaviors following future disturbance events.”

“The volcanic eruption at Kasatochi in 2008 provided the rare opportunity to document the response of a colonial seabird to the sudden and complete destruction of their nesting habitat. This study capitalized on that opportunity and gives us a glimpse into the ability of these species to disperse to nearby colonies and colonize new habitat,” adds the University of New Brunswick’s Heather Major, an expert on Aleutian seabirds who was not involved in the study. “This study is therefore important to our understanding of dispersal and habitat selection, and more generally, the ability of these two species to respond to large disturbances at their nesting colonies.”

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Biological responses of Crested and Least auklets to volcanic destruction of nesting habitat in the Aleutian Islands, Alaska is available at http://www.bioone.org/doi/full/10.1642/AUK-17-180.1 (issue URL http://www.bioone.org/toc/tauk/135/3).

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology that began in 1884 as the official publication of the American Ornithologists’ Union, which merged with the Cooper Ornithological Society in 2016 to become the American Ornithological Society. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

How to improve habitat conservation for migrating cranes

Tue, 04/24/2018 - 14:37

Every year, North America’s critically endangered Whooping Cranes travel back and forth along a 4,000-kilometer corridor linking their nesting grounds in Canada and their winter home in Texas. Habitat in their path through the northern Great Plains is being lost at an alarming rate to agriculture and other development, but the birds’ widely dispersed movements make identifying key spots for protection a challenge. Now, researchers behind a new study from The Condor: Ornithological Applications have created a model of Whooping Crane habitat use with the potential to greatly improve the targeting of conservation efforts during their migration.

Researcher Neal Niemuth and his colleagues used a database of Whooping Crane sightings in the region since 1990 to examine cranes’ habitat use in North and South Dakota. Analyzing the spatial patterns of the sightings, they found that Whooping Cranes prefer habitat that includes a mix of croplands and wetlands and are more attracted by a single large wetland basin than multiple smaller basins. Their results also show the effects of different conservation strategies across the region. East of the Missouri River, where efforts have been specifically targeted toward waterfowl conservation, lands under conservation management were more likely than other locations to be used by Whooping Cranes. West of the river, however, this was not the case.

Niemuth and his colleagues hope that their model can help to guide the siting of new wind, oil, and electrical transmission infrastructure to minimize potential conflicts with Whooping Cranes, as well as identifying opportunities for wetland restoration. According to the article, approximately $50 million per year is spent for habitat protection in the region, with much funding coming from sales of Duck Stamps. Because of their endangered status, Whooping Cranes have always been a priority in the area, but the quality and resolution of existing tools for targeting conservation and avoiding conflicts were low. The model presented in this publication provides biological linkages and increased spatial resolution that will increase effectiveness of Whooping Crane conservation efforts.

“Research on Whooping Crane habitat use throughout the migration corridor is crucial in helping us ensure that we are restoring and protecting habitat for a growing population of Whooping Cranes in the right places,” states Wade Harrell, the U.S. and Wildlife Service’s Whooping Crane Recovery Coordinator. “It is positive to see that the prairie pothole habitat in the Dakotas that the U.S. Fish & Wildlife Service is actively protecting for breeding waterfowl is also benefiting endangered species like the Whooping Crane.”

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Opportunistically collected data reveal habitat selection by migrating Whooping Cranes in the U.S. Northern Plains is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-80.1 (issue URL http://www.bioone.org/toc/cond/120/2).

About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology. It began in 1899 as the journal of the Cooper Ornithological Club, a group of ornithologists in California that became the Cooper Ornithological Society, which merged with the American Ornithologists’ Union in 2016 to become the American Ornithological Society. In 2016, The Condor had the number one impact factor among 24 ornithology journals.

About the U.S. Fish and Wildlife Service: The mission of the U.S. Fish and Wildlife Service is working with others to conserve, protect, and enhance fish, wildlife, plants, and their habitats for the continuing benefit of the American people. The findings and conclusions in the forthcoming article are those of the authors and the U.S. Geological Survey and do not necessarily represent the views of the U.S. Fish and Wildlife Service.

Nominees for BioOne Ambassador Award

Wed, 04/04/2018 - 17:18

The Auk and The Condor have each nominated a recent author for BioOne’s inaugural Ambassador Award, which will recognize “early career authors working to communicate the importance and impact of their focused research to communities beyond their fields of expertise.” Each of up to five winners will receive a $1000 cash award. More information can be found on BioOne’s website.

The Auk has nominated Emily Williams, lead author of the recent paper Patterns and correlates of within-season breeding dispersal: A common strategy in a declining grassland songbird (press release).

The Condor has nominated Andrew Dennhardt, lead author of the paper Applying citizen-science data and mark–recapture models to estimate numbers of migrant Golden Eagles in an Important Bird Area in eastern North America (press release).

We wish Emily and Andrew luck as the selection process for the awards continues!

Terns Face Challenges When They Fly South for Winter

Wed, 04/04/2018 - 11:45

A Common Tern wearing a geolocator. Photo credit: C. Henderson

The Common Tern is most widespread tern species in North America, but its breeding colonies in interior North America have been on the decline for decades despite conservation efforts. The problem, at least in part, must lie elsewhere—and a new study from The Auk: Ornithological Advances presents some of the best information to date on where these birds go when they leave their nesting lakes each fall.

The University of Minnesota’s Annie Bracey and her colleagues attached geolocators—small, harmless devices that record a bird’s location over time based on day length—to 106 terns from breeding colonies in Manitoba, Ontario, Minnesota, Wisconsin, and New York. When the birds returned to their breeding grounds in the following years, the researchers were able to recapture and retrieve data from 46 birds. The results show important migratory staging areas in the inland U.S. and along the Gulf of Mexico—a surprise, since it was previously thought that most Common Terns head for the Atlantic coast before continuing south. Birds from different colonies intermingled freely in the winter, but most ended up on the coast of Peru, suggesting that the population could be especially vulnerable to environmental change in that region.

For long-lived birds such as Common Terns, adult survival likely drives population trends more than breeding productivity, so identifying causes of mortality is crucial for effective conservation. Coastal Peru is vulnerable to multiple effects of climate change, including increasingly frequent and severe storms, changes in the availability of terns’ preferred foods, and rising sea levels. “Because survival is lowest during the non-breeding season, identifying coastal Peru as a potentially important wintering location was significant, as it will help us target studies aimed at identifying potential causes of adult mortality in this region,” says Bracey.

“This paper is both important and interesting, because it takes a species we consider ‘common’ and examines the reasons for its decline,” adds Rutgers University Distinguished Professor of Biology Joanna Burger, a tern conservation expert who was not involved in the research. “In short, this is one of the first studies that examines the entire complex of terns breeding in inland US locations, along with migratory routes, stopover areas, and wintering sites. It vastly increases our knowledge of the causes of declines and the locations and times at which terns are at risk, and more importantly, provides a model for future studies of declining populations.”

Migratory routes and wintering locations of declining inland North American Common Terns is available at http://www.bioone.org/doi/full/10.1642/AUK-17-210.1.

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology that began in 1884 as the official publication of the American Ornithologists’ Union, which merged with the Cooper Ornithological Society in 2016 to become the American Ornithological Society. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

Long-Term Study Reveals Fluctuations in Birds’ Nesting Success

Wed, 03/21/2018 - 09:47

Long-term data on Song Sparrows reveals factors that affect their nesting success. Photo credit: D. Janus

Understanding the factors that affect a bird species’ nesting success can be crucial for planning effective conservation efforts. However, many studies of nesting birds last only a few years—and that means they can miss the effects of long-term variation and rare events. A new study from The Auk: Ornithological Advances demonstrates this with nearly four decades of data from Song Sparrows in British Columbia.

The University of British Columbia’s Merle Crombie and Peter Arcese used 39 years of data from an island population of Song Sparrows to examine how the factors influencing their nesting success changed over long periods of time. Over almost 3,000 nesting attempts, 64% of which were successful, a number of patterns emerged. Some, such as the fact that older female birds were less successful, remained consistent over time. However, others, such as the effects of rainfall, population density, and nest parasitism, interacted with each other in complex ways that caused their importance to wax and wane over the decades, and inbreeding only became a significant negative factor when it increased sharply during the middle portion of the study. Unpredictable, rare fluctuations such as this can have large effects that shorter-term studies rarely capture.

“Researchers have been learning about the Song Sparrow population on Mandarte Island since 1960, and monitoring the population continuously since 1975,” says Arcese. “Because the population is semi-isolated, small, and resident year-round, we band all birds in the nest and have genotyped all nestlings since 1991.” A close focus on individuals, fitness, and relatedness in the Mandarte Song Sparrow population has allowed researchers to report the most precise demographic and population genetic parameters yet estimated in wild populations.

“Most studies of plant and animal populations in nature last three to five years, but ecological processes are often dramatically affected by climate and community change, which plays out over decades,” he continues. “Long-term studies like ours provide an invaluable record of change in population processes, which can help interpret the results of short-term studies of species not as easily studied as Song Sparrows.”

Temporal variation in the effects of individual and environmental factors on nest success is available at http://www.bioone.org/doi/full/10.1642/AUK-17-189.1.

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology that began in 1884 as the official publication of the American Ornithologists’ Union, which merged with the Cooper Ornithological Society in 2016 to become the American Ornithological Society. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

AUTHOR BLOG: Are All Eggs Created Equal? Saltmarsh Sparrows Support Gender Equality

Wed, 03/21/2018 - 09:47

Bri Benvenuti and Adrienne Kovach

Linked paper: Annual variation in the offspring sex ratio of Saltmarsh Sparrows supports Fisher’s hypothesis by B. Benvenuti, J. Walsh, K.M. O’Brien, M.J. Ducey, and A.I. Kovach, The Auk: Ornithological Advances 135:2, April 2018.

Three Saltmarsh Sparrow chicks banded as part of a study on offspring sex ratios. Photo: B. Benvenuti

In birds, females have the ability to control the sex of individual eggs; therefore, a mother may be able to choose whether she prefers each egg laid to be a male or female. This means that offspring sex ratios are not usually left to chance. From an evolutionary standpoint, this can be very beneficial, as different circumstances may favor the success of sons versus daughters.

But how does one know if it would be better to have more sons or daughters? Evolutionary theory suggests that if the potential benefits of raising one sex over the other vary in relation to environmental or maternal conditions, then females should favor the production of that sex. Typically, high quality sons are more beneficial to mothers, because they have the potential to produce far more grandchildren than daughters can (males can mate many times, but females are limited by how many eggs they can produce, incubate, and raise to fledging). More grandchildren = greater lifelong success.  Still, there is a risk to biasing offspring production toward sons; if the son is low quality (competitively inferior), he may not reproduce at all.  On the other hand, daughters tend to be “cheaper” to raise than sons. They need less resources to reach maturity, and if they survive, they almost always reproduce. With this in mind, one could logically say that producing daughters represents the “safe bet”—you might get a smaller payout (in terms of numbers of grandchildren), but you know you’ll get something.

Armed with this information, we chose to investigate whether Saltmarsh Sparrows manipulate the sex of their offspring based on environmental or maternal conditions as we would expect based on evolutionary theory. These tidal marsh specialist birds live a stressful life—they build nests in the marsh grasses just inches above the marsh surface that is regularly subjected to tidal flooding. Nests are more likely to escape these flooding events and successfully fledge offspring if they are timed to fledge within the 28 day lunar tidal cycle. Saltmarsh Sparrows are also one of the world’s most promiscuous birds, with almost every egg in a nest having a different father thanks to the scramble of competition among males for access to females. These characteristics provide interesting hypotheses in the context of evolutionary theory, so we asked, would Saltmarsh Sparrow mothers produce more sons, who would be larger and a) more likely to survive a nest flooding event and b) have the ability to produce more offspring through multiple matings? Or would they take the “safe bet” and produce more females?

To test our hypotheses, we collected nesting data from Saltmarsh Sparrow breeding locations in New England marshes over five years. We used DNA analysis to determine the sex of Saltmarsh Sparrow chicks and calculated the offspring sex ratio for our four study sites and across the whole study population. We then used a modeling approach to determine if there was an influence of environmental conditions (year, tidal flooding, precipitation), temporal effects (nest initiation in relation to flood tides, timing within the breeding season), or maternal condition on offspring sex ratios.

Surprisingly, we found an even offspring sex ratio of 1.03:1 (males to females) across all years and sites, and offspring sex ratios did not vary as a function of the environment, tidal flooding risk, or female condition. What we did find was an interesting pattern of annual variation between male and female bias that mirrored the adult sex ratio in the preceding year.

While numerous studies have provided evidence that female birds may have the ability to adjust offspring sex ratios in an adaptive way, we found no evidence for adaptive sex ratio manipulation in Saltmarsh Sparrows in relation to our hypotheses. Instead, the observed time-lagged relationship between offspring and adult sex ratio meets expectations of frequency-dependent selection, whereby females respond to higher frequencies of one sex by increasing production of the rarer sex, which would have a temporary fitness advantage. Our findings overall show support for balanced offspring sex ratios at a population level over time.

Scientists Remind Their Peers: Female Birds Sing, Too

Thu, 03/15/2018 - 10:08

Northern Cardinals are among the familiar North American bird species in which females sing in addition to males.

When North American ornithologists hear a bird singing, they’re likely to assume it’s a male. But in many species, the females sing too—and a new commentary in The Auk: Ornithological Advances argues that a better understanding of these unappreciated female songs could lead to advances in many aspects of bird biology.

Authors Karan Odom of Cornell University and Lauryn Benedict of the University of Northern Colorado both discovered the world of female birdsong through their own research. “I started studying California towhees 17 years ago, and I was fascinated by the duet vocalization given by females and males,” says Benedict. “That led me to start looking for female song in other North American bird species, and I was surprised to learn that it was much more common than I expected. The reports of female song are buried in odd corners of the literature, but when you put them all together, you start to see some interesting patterns.”

Though singing females were likely the norm among the ancestors of today’s songbirds, female song today is understudied and is underrepresented in collections of bird sound recordings. This, say Odom and Benedict, may be result of bias toward the world’s temperate regions—though more widespread in temperate species than many ornithologists appreciate, female song is most common among tropical birds. They argue that better documentation of which species female song is present in and more detailed descriptions of female song structure and output could improve our understanding of birds’ comparative physiology, neurobiology, behavioral ecology, evolution, and even conservation. Birds of conservation concern are often located and identified by song during surveys, and assumptions that all singing birds are male could mislead wildlife managers about the state of populations.

Odom and Benedict urge their fellow ornithologists to spread the word that female birds sing, to share resources, and to disseminate their findings. You don’t need to be a professional ornithologist in order to help expand our knowledge of female song, either—Odom has created a website where any birdwatcher can upload their observations. “If you hear a bird singing, do not assume it’s a male,” she says. “If you observe a female bird singing, document it by uploading field notes, audio, or video to the collections on our website, femalebirdsong.org. Make sure to indicate how you recognized the bird was female.”

“Odom and Benedict have written an excellent appeal to document and record more female bird song,” adds Leiden University’s Katharina Riebel, a former collaborator of Odom’s. “They rightly point out that the extent of female bird song has been starkly underestimated, as almost by default we assume that a singing bird must be the male of the species. As a consequence, we might have missed out many aspects and the dynamics of male and female vocal signaling in songbirds—clearly, there is still lots to discover! I am confident that ornithologists in the field can make substantial contributions toward these questions by sharing their observations and recordings, as I very much hope this article will encourage them to do.”

A call to document female bird songs: Applications for diverse fields is available at http://www.bioone.org/doi/full/10.1642/AUK-17-183.1.

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology that began in 1884 as the official publication of the American Ornithologists’ Union, which merged with the Cooper Ornithological Society in 2016 to become the American Ornithological Society. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

AUTHOR BLOG: Recognizing the Importance of Female Birdsong

Thu, 03/15/2018 - 10:08

Karan Odom & Lauryn Benedict

Linked paper: A call to document female bird songs: Applications for diverse fields by K.J. Odom and L. Benedict, The Auk: Ornithological Advances 135:2, April 2018.

House Wrens are among the familiar birds in which females sing. Photo credit: J. Hudgins/USFWS

Can you name ten North American or European bird species in which females sing? Can you name twenty? Fifty? That may seem like a lot, but in fact it’s only a small percentage of temperate-zone bird species with female song. There are at least 144 North American passerine species with female song, and many more non-passerines with elaborate vocalizations that could be classified as song (defining “song” is a topic we won’t even go into here!). Across all avian species, approximately 64% have female song, but these estimates are rough. The true numbers could be much higher. Why are the estimates so rough? Because documentation and reports of female song are lacking. We highlight this problem in our paper “A call to document female bird songs: Applications for diverse fields.” We ask all of you to help us address the deficit.

We know that the data are out there; we regularly have conversations with ornithologists and citizen scientists who tell us that they have observed singing females in myriad species. Our response: Publish it! Archive it! We’ve chatted with many senior researchers who have years of data including observations and recordings of female song in their study populations, but who haven’t published these data because female song is rare or is not their main research focus. We’ve also heard from students working as field assistants whose cohorts regularly observe singing females, but those observations are seldom documented. On field projects with many technicians, word-of-mouth data can be extensive and highly informative, but staff turnover means that known population traits never get put down on paper (or audio).

Citizen scientists frequently tell us about singing females, and many of them have taken the next step to document their observations through The Female Bird Song Project. Contributors have recorded female song in species as diverse as the Mexican Sheartail (Doricha eliza), Black-goggled Tanager (Trichothraupis melanops), Saffron Finch (Sicalis flaveola), and Cerulean Warbler (Setophaga cerulea), all of which seem to be the first documentation of female song in their species!

Each of these contributions plays a role in understanding the distribution of species with female song – data that researchers can use to address a wide range of biological questions. A complete picture of when and how female birds sing will offer insights into the biological mechanisms, evolution, and applications of avian vocal signals. Neurobiologists can ask how bird brains perceive and produce these variable signals, and whether that differs by sex. Evolutionary ecologists can ask why songs differ among species with different ecology and life-history traits. Conservation biologists can use songs to census and monitor the presence of males and females across populations.

What can you do? Don’t assume that a singing bird is a male. Look, listen, and document without bias. Teach your students to do the same. In 73% of all bird species we lack enough published information to even determine whether females sing. We are confident, however, that in some of those species females do sing because we have talked to colleagues about them. Common knowledge suggests that female song is rare, but our experiences make us question that: if all ornithologists talked to each other about female song the way that they talk to us, then that assumption would change. Your random observations of a female warbler singing can probably be backed up by the observations of many others. Females of temperate-breeding species may not sing as often as males, but when we pool all our knowledge and observations it’s likely that we’ll find more parity than we expect.

AUTHOR BLOG: Latitudinal Gradients in Bird Survival

Tue, 03/13/2018 - 16:25

Gonçalo Ferraz

Linked paper: Age effects on survival of Amazon forest birds and the latitudinal gradient in bird survival by A.P. Muñoz, M. Kéry, P.V. Martins, and G. Ferraz, The Auk: Ornithological Advances 135:2, April 2018.

A Guianan Warbling Antbird, Hypocnemis cantator, banded and ready for release. Photo credit: E. Johnson

Bold, recurring patterns are fascinating, and more so if they are unexplained. For biologists living in the tropics, perhaps the most striking examples are the various latitudinal gradients in community and life history metrics. Science excites our curiosity in the search for universal rules, but large-scale latitudinal patterns hint that some things may be fundamentally different in different parts of the world. Could there be really such a thing as “tropical biology”?

One of the best-documented of these latitudinal gradients is the tendency for avian clutch size to increase with increasing latitude. Since there is no evidence that high-latitude populations grow faster than equatorial ones, it’s been widely assumed that some other life history trait must also change with latitude to compensate for the variation in clutch size. Thus, throughout the second half of the 20th century, the idea that adult tropical birds live longer than their temperate counterparts became widely accepted among ornithologists.

A Rufous-throated Antbird, Gymnopithys rufigula. Photo credit: E. Johnson

The acceptance of a latitudinal gradient in survival, however, was more based on common sense than hard data—so much so that when Karr et al. (1990, The American Naturalist 136: 277-291) challenged the idea in a paper subtitled “Will the dogma survive?” there were not many voices sounding in defense of the “dogma.” Indeed, two decades later, Corey Tarwater and colleagues suggested that, if there is no latitudinal trend in the survival of adult birds, there could be a trend in the survival of juveniles (2011, Ecology 92: 1271-1281). Their work drew on detailed analysis of age-dependent survival in one Central American passerine species and proposed that tropical juveniles survive more than temperate juveniles. If adult survival shows no relationship with latitude this implies relatively little difference between adult and juvenile survival in the tropics.

For a paper just published in The Auk, Alejandra P. Muñoz, myself, and our colleagues used bird banding data to tackle the problem of the latitudinal gradient in bird survival on two fronts. First, we quantified the effect of age on survival for forty species of Amazon forest passerines, showing that adults at our tropical site had substantially higher survival probabilities than juveniles. Second, we compared our adult survival estimates with estimates from 175 species from Peru to Alaska and found that survival does decrease with increasing latitude. This latitudinal effect persists even after accounting for effects of migration mode, phylogeny, and time of data collection, and we conclude that the latitudinal gradient in survival is a fact after all, at least as seen among New World forest passerines.

Our work benefited a great deal from two recent advances. First, there is an ongoing transformation in how tropical ornithologists assess bird age. The Wolfe-Ryder-Pyle molt-cycle system, which we employed, is extremely useful for aging birds in populations that have poorly delimited breeding periods, which is typical of tropical regions. This was central for quantifying the effect of age on survival. Second, we tapped into the phenomenal database of Vital Rates of North American Birds made available by the Institute of Bird Populations (IBP), enabling us to include data from as far north as Alaska. The IBP estimates, combined with a wealth of tropical passerine survival estimates published since 1990, made it possible to take up Karr et al.’s (1990) challenge anew.

From the analytical perspective, we used a multi-species Cormack-Jolly-Seber (CJS) approach, a standard method for estimating apparent survival from capture-recapture data on open populations, to model our Amazon data. We treated each of the forty species in our dataset as a random draw from a wider distribution of species, and the inference about age effects was made at the level of this wider distribution, strengthening the generality of the conclusions. The CJS accounts for the possibility of capture failure, and a “mixture” component of the model, developed by co-author Marc Kéry, makes it possible to incorporate birds of unknown age in the analysis. Our work thus addresses a variety of sources of uncertainty before reaching its final conclusions.

The observation of a latitudinal trend in survival probability helps explain the maintenance of a latitudinal trend in clutch size, but it need not be the only explanation. It’s also possible, for example, that the number of clutches laid each year also varies with latitude in association with the length of the breeding season. With or without latitudinal change in number of clutches, one cannot tell whether the variation in survival we documented is a sufficient explanation for the current variation in clutch size. What’s more, even if one explains the maintenance of current variation, there is still the question of how that variation evolved. There is certainly still much to explore in the latitudinal variation of bird life history traits.

Long Incubation Times May Defend Birds Against Parasites

Wed, 02/21/2018 - 12:12

Some tropical birds have longer egg incubation times than their temperate cousins, even though their habitat is teeming with egg-eating predators. The reason why has long been a mystery, but a new study from The Auk: Ornithological Advances applies new methods to confirm the evidence for an old hypothesis—that a longer development period leads to a stronger, more efficient immune system.

The University of Missouri-St. Louis’s Robert Ricklefs first studied this relationship in the early 1990s, using data from microscopic examination of avian blood samples for the presence of parasites, primarily those that cause malaria. He found that the longer a species’ incubation period, the lower its prevalence of parasites. However, Ricklefs remained concerned that especially low parasite loads could have been missed during microscope examination, affecting parasite prevalence estimates.

Advances in DNA sequencing offered a new solution. For their new study, Ricklefs and his colleagues collected blood samples from birds in the eastern U.S. and several Neotropical countries and checked for the presence of parasite DNA, tabulating how many individuals from various families of birds were sampled at each site and how many were infected with Haemoproteus or Plasmodium parasites. About 22% of individual birds in both temperate and tropical regions had parasite DNA in their blood. While incubation time varies little among temperate species, it does vary among tropical species, and in tropical birds parasite prevalence was significantly lower in species with longer incubation times.

These results confirm those of the old blood smear analysis. While there is still no direct evidence for the hypothesis that a longer incubation time promotes a stronger immune system, this correlation provides a strong hint that this could indeed be the solution to the mystery of why the embryos of some tropical birds take so long to develop. “My interest in blood parasites was stimulated by a former graduate student, Victor Apanius, primarily in the context of community ecology. However, I had been working on the diversification of avian life histories, particularly embryo and chick growth rates, and I couldn’t help but notice a connection between the two,” says Ricklefs. “I wasn’t surprised that the new results confirm the old ones so well, really, because the two techniques estimate the same attribute. However, more detailed studies of the avian immune response and how variation in host defense is related to development certainly are warranted.”

“This paper is a nice follow up the 1992 study that showed an inverse relationship between parasite prevalence and egg incubation period. Since that time, PCR methods have been developed that detect more infections than microscopy, and the work is important because it verifies the previous results with revised methods,” according to San Francisco State University’s Ravinder Sehgal, an expert on avian blood parasites who was not involved in the study. “Moreover, it renews interest in a phenomenon that has gone largely unexplored. It will be now be important to test the work in an experimental system, to study the parasitology and explore the tradeoffs between embryo growth rate and immune function.”

Duration of embryo development and the prevalence of haematozoan blood parasites in birds is available at http://www.bioone.org/doi/full/10.1642/AUK-17-123.1.

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology that began in 1884 as the official publication of the American Ornithologists’ Union, which merged with the Cooper Ornithological Society in 2016 to become the American Ornithological Society. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

Are Flamingos Returning to Florida?

Wed, 02/21/2018 - 12:10

American Flamingos should be considered native to Florida, argue the authors of a new review. Photo credit: J. Patterson

Flamingos are a Florida cultural icon, and sightings of American Flamingos in the state have been on the rise in recent decades. However, whether they’re truly native to the U.S. or only arrive via escape from captivity has long been subject to debate, making developing a plan for managing Florida’s flamingo population challenging. A new study from The Condor: Ornithological Applications reviews the evidence and provides a fresh argument that the birds should be considered part of the Sunshine State’s native fauna.

Zoo Miami’s Steven Whitfield, along with colleagues from Audubon Florida’s Everglades Science Center, the National Park Service, Big Cypress National Preserve, and the Rookery Bay Estuarine Research Reserve, reexamined the historical evidence of flamingos in Florida and evaluated the likely origins of birds seen in recent years. Overall, they conclude, the evidence from both narrative accounts and museum records suggests that American Flamingos once occurred naturally in large flocks in Florida and probably even nested there before being eliminated by hunting around 1900. From 1950 to the present, however, birdwatchers have reported almost 500 new observations of flamingos in Florida, with both flock size and the frequency of observations increasing over time. While it’s plausible that some of these individuals could be escapees from captive flocks, there is also strong evidence for dispersal from wild populations in Mexico and the Caribbean.

The population history Whitfield and his coauthors describe is consistent with that of some native species already protected by state and federal endangered species laws, and they hope that their study will lead to a better plan for managing wild flamingos in Florida. “Living in Florida, you see flamingos everywhere—in advertising, in place names, even on the logo for the state lottery—but as an actual organism, as a species, there was essentially no information available on the biology of flamingos,” says Whitfield. “Some biologists considered them native birds that were extirpated during the plume trade of the late 1800s, and urged for population recovery measures, while others considered the rare flamingos seen around Florida to be escapes from captive colonies. We often say that in south Florida we have just two types of species, introduced and endangered, but a species can’t be both at the same time.”

“This article finally sheds welcome light on status of these iconic birds in Florida. The authors meticulously researched historic records and compiled more recent sightings to reconstruct the history and population trends of flamingos in Florida,” adds the American Museum of Natural History’s Felicity Arengo, a flamingo conservation expert who was not involved in the study. “Flamingo numbers have increased notably since the 1950s due to protections to species and habitats in Florida and throughout the Caribbean. The authors are cautious and recognize the limitations of the data in their study, but they provide ample evidence that Florida was the northernmost extent of the American Flamingo prior to the early 1900s and that populations have been recovering.”

Status and trends of American Flamingos (Phoenicopterus ruber) in Florida, USA is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-187.1.

About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology. It began in 1899 as the journal of the Cooper Ornithological Club, a group of ornithologists in California that became the Cooper Ornithological Society, which merged with the American Ornithologists’ Union in 2016 to become the American Ornithological Society. In 2016, The Condor had the number one impact factor among 24 ornithology journals.

Fracking Tied to Reduced Songbird Nesting Success

Wed, 02/14/2018 - 09:29

A researcher handles a Louisiana Waterthrush chick. Photo credit: M. Frantz

The central Appalachian region is experiencing the country’s most rapid growth in shale gas development, or “fracking,” but we’ve known almost nothing about how this is affecting the region’s songbird populations—until now. A new study from The Condor: Ornithological Applications demonstrates that the nesting success of the Louisiana Waterthrush—a habitat specialist that nests along forested streams, where the potential for habitat degradation is high—is declining at sites impacted by shale gas development in northwestern West Virginia.

West Virginia University’s Mack Frantz and his colleagues mapped waterthrush territories and monitored nests along 14 streams from 2009 to 2011 and again from 2013 to 2015. They also mapped and measured disturbances to streams and to the forest canopy, using aerial photographs and satellite imagery as well as extensive ground-truthing, and classifying them according to whether they were related to shale gas development. Their results show that as shale gas development has expanded in the area, nest survival and productivity and riparian habitat quality have declined. At the same time, the size of individual waterthrush territories has increased, suggesting birds need to range farther to find sufficient resources. This study is one of the first to demonstrate that shale gas development can affect songbird reproductive success and productivity, both directly through the presence of fracking infrastructure and indirectly through effects on habitat quality.

“I hope our findings lead to robust protections of our forested headwater stream ecosystems, which are currently overlooked for regulation despite their critical role in providing nutrients and organic matter downstream, not to mention as an important source for drinking water,” says Frantz. “Waterthrushes are a modern-day ‘canary in the coal mine,’ and there are many more opportunities to study how anthropogenic disturbance affects and entangles food webs at the aquatic–terrestrial interface.”

“After twelve years of research conducted with this species, I have seen the numerous impacts hydraulic fracturing has had on waterthrush survival and the toll that the industry has had on our nation’s wild places and wildlife,” adds Louisiana State University-Alexandria’s Leesia Marshall, a waterthrush expert who was not involved in the Condor study. “This paper should serve as a call for all scientists to redouble efforts across all related disciplines to document the present impacts of shale gas extraction and to develop strategies for mitigation and avoidance of potential impacts in the future.”

Demographic response of Louisiana Waterthrush, a stream obligate songbird of conservation concern, to shale gas development is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-130.1.

About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology. It began in 1899 as the journal of the Cooper Ornithological Club, a group of ornithologists in California that became the Cooper Ornithological Society, which merged with the American Ornithologists’ Union in 2016 to become the American Ornithological Society. In 2016, The Condor had the number one impact factor among 24 ornithology journals.

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