You are here

Research From The Auk and The Condor

Subscribe to Research From The Auk and The Condor feed Research From The Auk and The Condor
The official blog of ornithology journals The Auk and The Condor
Updated: 52 sec ago

Penguins’ Calls Are Influenced by Their Habitat

Wed, 11/01/2017 - 13:32

Variation in Little Penguins’ agonistic calls appears to be driven by the habitats where they live. Photo credit: D. Colombelli-Négrel

Birds use vocalizations to attract mates, defend territories, and recognize fellow members of their species. But while we know a lot about how variations in vocalizations play out between populations of songbirds, it’s far less clear how this variation affects birds such as penguins in which calls are inherited. A new study from The Auk: Ornithological Advances examines differences in the calls of Little Penguins from four colonies in Australia—nocturnal birds for whom vocalizations are more important that visual signals—and finds that disparities in habitat, rather than geographic isolation or other factors, seem to be the key driver of variation in the sounds these birds use to communicate.

Diane Colombelli-Négrel and Rachel Smale of Australia’s Flinders University recorded calls from four Little Penguin populations across a small area of South Australia, one of which had previously been shown to have subtle genetic differences from the other three, and used playback experiments to test penguins’ ability to distinguish between calls from different colonies. They found that agonistic calls, which are used in pair displays and aggressive situations, varied among the four populations, and that the calls’ characteristics appeared to depend on small-scale differences in the habitat where the penguins lived. However, birds did not discriminate between calls originating from different colonies, which suggests that agonistic calls don’t seem to play a role in isolating the two different genetic groups.

Penguins breeding in open habitats produced lower-frequency calls than those breeding in habitats with denser vegetation—the opposite of the trend typically observed in songbirds. The authors speculate that agonistic calls may be subject to different selective pressures because they’re used in close encounters with other birds rather than to communicate across distances, and could also be influenced by variation in the noise level of wind and surf. “I was excited to find that calls were influenced by habitat, as this hasn’t been investigated much in seabirds and most of our knowledge in this area comes from studies on songbirds,” says Colombelli-Négrel. “This new research suggests that many factors influence call variation in birds, which also depends on the function of the calls. This study highlights that many questions remain and that studies need to investigate more than one factor in conjunction with the function of the calls to fully understand call variation in seabirds.”

“This work tells an interesting story of vocal diversification in Little Penguins, and gives insight into how individual and micro-scale variation effects behavior,” according to Stony Brook University’s Heather Lynch, an expert on penguin calls who was not involved in the study. “Non-vocal-learning birds are relatively understudied in terms of vocalizations, and it is great to see penguin vocalizations being studied in such a way.”

Habitat explained microgeographic variation in Little Penguin agonistic calls is available at http://www.bioone.org/doi/full/10.1642/AUK-17-75.1.

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.


Translocated Hawks Thrive in Hispaniola

Thu, 10/26/2017 - 17:38

A Ridgway’s Hawk on the island of Hispaniola. Photo credit: R. Thorstrom

Species translocation—capturing animals in one place and releasing them in another—is a widely used conservation method for establishing or reestablishing populations of threatened species. However, translocation projects often fail when the transplanted animals fail to thrive in their new home. A new study from The Condor: Ornithological Applications demonstrates how close monitoring of the animals being released into a new area is helping wildlife managers gauge the success of their effort to save the Ridgway’s Hawk of Hispaniola.

Ridgway’s Hawk is a critically endangered raptor endemic to the Caribbean island of Hispaniola. Since 2009, the Peregrine Fund has translocated 104 nestlings from the species’ stronghold in a national park to a protected resort area called Punta Cana 130 kilometers away. They monitored the birds after their release, tracking their survival and breeding success, as well as collecting the same data on 36–110 breeding pairs per year in the original national park population. Survival rates were high in both locations, and more young hawks began breeding on the resort property, probably because more territories were available due to the birds’ low numbers.

Lead author Chris McClure of the Peregrine Fund and his colleagues believe that the “soft release” method they use with the translocated birds, involving an adjustment period where young birds are allowed to come and go freely but are provided with food, has contributed to the success of the project. Post-release monitoring has been a valuable tool for gauging their success and planning future conservation efforts, and they hope that more wildlife managers will consider incorporating this into their plans when seeking funding for translocation projects. “Our results show that the new population of Ridgway’s Hawks in Punta Cana is taking hold, but we only know that because of the hard work of our staff and volunteers in tracking these birds,” says McClure. “I think our study is a great example of monitoring to ensure that conservation goals are actually achieved.”

“The paper is a good example of the important role of post-release monitoring in translocation projects,” adds Massey University’s Doug Armstrong, an expert on reintroduction programs who was not involved in the study. “It is easy for people to invest a lot of effort into well-meaning but ineffectual translocations projects if they aren’t monitored. This paper illustrates how state-of-the-art methods can be applied to provide clear and useful information of post-release survival and recruitment.”

Successful enhancement of Ridgway’s Hawk populations through recruitment of translocated birds is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-77.1.

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.


AUTHOR BLOG: Migrating Birds That Eat Northern Spicebush Berries Are Fat and Healthy Birds

Mon, 10/23/2017 - 09:22

Yushi Oguchi

Linked paper: Fruits and migrant health: Consequences of stopping over in exotic- vs. native-dominated shrublands on immune and antioxidant status of Swainson’s Thrushes and Gray Catbirds by Y. Oguchi, R.J. Smith, and J.C. Owen, The Condor: Ornithological Applications 119:4, November 2017.

Collecting a small blood sample from a Gray Catbird to assess its health during stopover. Photo credit: Zak Pohlen

“We should not only conserve avian populations; we should conserve ‘healthy’ avian populations.”  – Dr. Jen C. Owen (my M.S. adviser, Michigan State University)

We investigated whether the health status of fall frugivorous Swainson’s Thrushes and the Gray Catbirds differed depending on their use of shrublands dominated by exotic versus native plants. In the process, we came to appreciate the value of one native fruit, northern spicebush (Lindera benzoin), a fruit we couldn’t even identify at first. Our story represents a unique insight that ecophysiology can bring to conservation science and habitat management.

Our prediction was that habitat may influence bird health through their frugivorous diet and that landbird migrants may be able to enhance their immune system by resting and refueling during stopover. In fall, many shrubs are loaded with fruit, and this fruit contains essential nutrients, including antioxidants, which help a bird neutralize reactive oxygen species produced during exercise (flight).

A question of conservation interest is whether birds that forage on exotic fruits and in exotic-dominated shrubland experience a deleterious effect on their health. Many exotic shrubs such as autumn olive and honeysuckle (introduced to the Midwestern U.S.A.) produce fruits that are generally lower in energy than native fruits such as northern spicebush, but some exotic fruits may have high antioxidants, including immunostimulatory carotenoids. We wouldn’t know unless we tested it!

A state-managed land in Michigan had the perfect habitat matrix—exotic-dominated shrubland and native-dominated shrubland occurring side by side, bisected by woodland. The exotic habitat was largely autumn olive, honeysuckle, and multiflora rose, and the native habitat was largely dogwood species, common winterberry, and northern spicebush. During fall migration in 2012 and 2013, we captured more than 800 individual birds, from which we collected blood samples for comprehensive health assessments.

Where Swainson’s Thrushes foraged during stopover had no impact on their health. On the other hand, Gray Catbirds using exotic shrubland experienced poor health; they lost mass and had reduced immune function and lower antioxidant capacity compared to catbirds using native shrubland. We also saw annual variation, with catbirds exhibiting more deleterious effects in 2013 compared to 2012. We further found that the pattern of habitat effect on catbird (but not thrush) health could be at least partly predicted based on the fruits they ate (math on fruit nutrition and bird fecal data).

Fecal sample showing the remnants of northern spicebush. Photo credit: Jen Owen

It is through this nutritional analysis that we saw the value of northern spicebush. Spicebush fruit has very high energy and antioxidant capacity relative to other species. It was a preferred fruit by both bird species and likely contributed to the bulk of the nutrients they acquired in native shrubland. In exotic shrubland, thrushes consumed more exotic fruits like common buckthorn than catbirds did—so they got antioxidants from exotic fruits. Catbirds, apparently more “reluctant” than thrushes to eat exotic fruits, instead consumed other native fruits that were low in antioxidants. Not eating enough exotic fruits in exotic shrubland may be why catbirds experienced a dip in their health there.

To summarize, migrant health may be influenced by human alteration of habitat, and the effects may depends on the diet of the birds. And again, northern spicebush is a great fruit for birds if you are in eastern North America! In a future paper (accepted by The Condor), we will cover more on shrubland habitat use by the birds at our site.

Dr. Jen Owen continues to direct the Burke Lake Banding Station (BULA) where this research was conducted. She and her undergraduate researchers are doing more intensive monitoring of the fruit abundance and phenology at the site, particularly on the interannual variation in spicebush fruiting in relation to climate. BULA is now in its 7th year of operation, and it continues to provide research opportunities for many students as well as inspiring bird enthusiasts of all ages. Visitors are always welcome while they are open during fall and spring migration. Check them out on their website (burkelakebanding.com) or like them on Facebook (facebook.com/BULAbandingstation).

I’ve done a return migration to the University of Wisconsin–Madison for my Ph.D. this fall. Following my renewed interest in nutrient acquisition so key to health, I now study molecular mechanisms of digestive enzyme modulation in the avian gut.


AUTHOR BLOG: Citizen-Science Data and Capture-Mark-Recapture Models to Estimate Numbers of Rare Species

Wed, 10/18/2017 - 16:01

Andrew Dennhardt

Linked 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 by A.J. Dennhardt, A.E. Duerr, D. Brandes, and T.E. Katzner, The Condor: Ornithological Applications 119:4, November 2017.

Have you ever looked to the autumn sky above and wondered how many of your favorite feathered friends are out there, as they migrate southward each year? If so, then you are not alone. A common goal in ecology has been to estimate the abundance of wild populations. From basic counts to educated guesses, historically, people have tried it all. During and even before the work of Sir Ronald Fischer, the father of modern statistics, applied mathematics aided in population estimation—for humans and wild animals alike.

F.C. Lincoln (1930) is credited with one of the first modern attempts to approximate population abundance of wild animals based on a sample of marked individuals (Bailey 1952, Le Cren 1965). The premise of his approach, co-credited to C. G. Johannes Petersen (1894) and commonly called capture-mark-recapture (CMR), was simple: trap a random set of animals of the same species in an area, mark those you caught with a unique tag, release them back into the wild for a period of time, return to the same area once more and randomly trap individuals of that same species again, and record which previously tagged individuals, if any, came back to the area. In brief, when you know the proportion of individuals you recaptured the second time, you can assume that you trapped the same proportion of the total population when you trapped the first time. The math is straightforward, too: if you have an initial sample of animals captured, marked, and released back into the wild, M, and multiply that by the total number of animals sampled a second time, n, then you can divide that quantity by the number of marked animals in that second sample, m, and approximate true population size, N.

In our paper, we used modern statistical advancements in CMR to estimate abundance of Golden Eagles (Aquila chrysaetos), a species of conservation concern in the United States, using an unusual approach. In effect, we did not physically capture, mark, or recapture individual animals in the wild; rather, we did so virtually in a computing environment with the help of observational data collected by some savvy citizen-scientists.

Golden Eagles in eastern North America face lethal and sub-lethal threats, many of which are human caused. However, these eagles are rarely seen, broad-ranging, and difficult to capture in the wild because they often avoid areas of human activity. Despite this fact, citizen-scientists observe Golden Eagles frequently and regularly during their annual spring and autumn migrations in Pennsylvania, U.S.A. Moreover, Golden Eagle movements are highly stereotyped, especially in autumn, bringing them within a few hundred meters of hawk counters on ridgetops in the Appalachian Mountains. Better still, because of past telemetry studies, we know how fast Golden Eagles fly when they migrate. Hawk counters collect their data on Golden Eagles and other migrant species and archive their observations in an online database, hawkcount.org. With assistance from managers of the archive, our research team gained permission and access to download historic count data on migrating Golden Eagles observed using the Kittatinny Ridge during their peak migration period, November, over a 10 year period from 2002 to 2011.

Now, here’s where things get really exciting (well, they do for me, at least!). Because (a) historic hawk-count data included information on the timing of Golden Eagles migrating southward past monitoring sites along the Kittatinny, (b) telemetry data gave us an idea of how fast they fly while migrating in autumn, and (c) we could measure the distance between each of the monitoring sites they passed, we could then estimate how long it would take eagles to travel between pairs of sites. Using a customized computer program, we matched records of Golden Eagles together, from site to site, such that we could know when observers at one site counted a bird that had probably been counted at a previous site (i.e. eagles became “captured,” “marked,” and “recaptured”).

Using these virtual data on matched eagle observations, we developed what are commonly called encounter histories. In brief, encounter histories comprise a sequence of 1s and 0s unique to each eagle. In a given sequence, a 1 represents either the event of first “capture and marking” or a subsequent “recapture” after being previously marked and released back into the wild, and a 0 represents an event when an eagle was not “captured or recaptured” at a previous or subsequent migration monitoring site. For modern CMR approaches, extensions of Lincoln (1930) and Petersen’s (1894) early work, encounter histories are the necessary input data for a statistical model. Because we were interested in estimating eagle abundance in a particular area (i.e. the Kittatinny Ridge) over time, we chose the Population Analysis (POPAN) Jolly-Seber model—the right tool for the job.

Most exciting for us, our methodology worked. We produced population abundance estimates for Golden Eagles migrating along the Kittatinny Ridge each autumn. To boot, two sets of our estimates followed the necessary rules (e.g., statistical model goodness-of-fit tests) for us to consider them reliable by modern CMR standards. Together, our best models estimated that approximately 1,350 Golden Eagles migrated along the Kittatinny Ridge each November, 2002–2011.

In the end, we feel that we have produced a useful framework for evaluating other migratory bird populations based on similar data and known movement behaviors. Our proposed methodology not only builds upon the legacy of modern CMR work, but is also far more cost-effective than physical CMR and other costly survey techniques. In the case of fixed-wing aircraft surveys for Golden Eagles in the western United States alone, our work costs far less than the annual ~$320,000 necessary to implement such surveys. Most importantly, such an achievement was only made possible by the tireless work of numerous dedicated citizen-scientists, whose standardized and centrally managed data can provide wildlife researchers and managers with quality information useful in conservation decisions. To our friends at the Hawk Migration Association of North America, for all of their data collection and management year-in and year-out, our team is abundantly grateful—pun intended!

References

Bailey, N. T. J. 1952. Improvements in the interpretation of recapture data. Journal of Animal Ecology 21:120–127.

Le Cren, E. D. 1965. A note on the history of mark-recapture population estimates. Journal of Animal Ecology 34:453–454.

Lincoln, F. C. 1930. Calculating waterfowl abundance on the basis of banding returns. Circulation of the U.S. Department of Agriculture No. 118.

Petersen, C. G. J. 1894. On the biology of our flat-fishes and on the decrease of our flat-fish fisheries: with some observations showing to remedy the latter and promote the flat-fish fisheries in our seas east of the Skaw. Report of the Danish Biological Station No. IV (1893–94).


How Many Golden Eagles Are There?

Wed, 10/18/2017 - 16:00

Photo credit: D. Brandes

For conservation efforts to be effective, wildlife managers need to know how many individuals of a species are out there. When species are spread out over large areas and occur at low densities, as is the case with the Golden Eagle, figuring this out can be tricky. However, a new study from The Condor: Ornithological Applications applies an old technique called “mark-recapture” in a novel way, eliminating the need to actually capture and mark eagles but instead, using math that allows scientists to turn individual observations into population estimates.

West Virginia University’s Andrew Dennhardt, Adam Duerr, and Todd Katzner and Lafayette College’s David Brandes used observations made by volunteer “citizen-scientists” of Golden Eagles migrating along a single, long mountain ridgeline in Pennsylvania to estimate the total number of eagles passing through the area each year. To do this, they developed a new way to apply a classic ecology tool called mark-recapture analysis—capturing and marking a portion of a population, and then counting the number of marked individuals in another group captured later. Helped by the fact that observers were often able to categorize individual eagles as either immature or adult birds, the scientists were able to identify instances of individual eagles being sighted at more than one location as they made their way south along the ridge over the course of a day, treating these subsequent sightings as “recaptures.”

Volunteers reported more than 3,000 sightings of Golden Eagles at five count sites along the ridge from 2002 to 2011. The analysis used in the study, which lets researchers estimate how many birds were missed as well as how many were seen more than once, suggests that these sightings represented between 2,592 and 2,775 individual eagles over the ten year period, with approximately 1,300 passing through the area on average in a given year. Past studies indicate that the total population of eagles breeding in Quebec and migrating through Pennsylvania is around 5,000, making this about a quarter of the larger population. Because the eagles are difficult to count on their breeding grounds, however, better methods for tracking their numbers during migration represent a significant advance.

“Conservation of Golden Eagles in eastern North America is a really important goal for lots of reasons—it is a small, historically declining population, at risk from anthropogenic threats and habitat loss. A central part of that conservation goal is figuring out how many of the darn things there are. Andrew’s work is the first empirical estimate of golden eagle population size,” says Katzner, now a Research Wildlife Biologist at the US Geological Survey. “Nothing quite like this has ever been done. We’ve taken a standard tool, mark–recapture, and turned it on its head to give us a new way to estimate population size.”

“For me, this was a dream come true, because I got to work on a project relevant to the conservation of the species that originally inspired me to enter the field of wildlife ecology and management,” says Dennhardt, now at Michigan State University. “Partnerships between researchers and citizen-scientists can help improve wildlife management decisions to address threats to migratory Golden Eagles and other species. I hope this work inspires future researchers to evaluate the populations of other migratory species, and that it encourages the greater scientific community to consider new and existing citizen-science programs and think about how such programs’ data might be used in their own research toward improving resource management and decision making.”

Applying citizen-science data and mark–recapture models to estimate numbers of migrant Golden Eagles in an Important Bird Area in eastern North America is available at http://www.bioone.org/doi/full/10.1650/CONDOR-16-166.1.

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.


AUTHOR BLOG: How Canada Warblers Keep Up with the Joneses

Wed, 10/18/2017 - 15:59

Anjolene Hunt

Linked paper: Forestry and conspecifics influence Canada Warbler (Cardellina canadensis) habitat use and reproductive activity in boreal Alberta, Canada by A.R. Hunt, E.M. Bayne, and S. Haché, The Condor: Ornithological Applications 119:4, November 2017.

Could a behavioral phenomenon, like the tendency of birds to live near neighbors, change the way we think about the effects of habitat disturbance? Results from new paper in The Condor: Ornithological Applications suggest that for Canada Warblers, this may be the case.

These iconic, brightly colored boreal songbirds are declining in number. Habitat loss and degradation are likely the main culprits. While it is true that forestry changes the landscape across much of the Canada Warbler breeding range, it remains contentious whether this results in habitat loss or whether they will use and thrive in regenerating postharvest areas. We suspected this discrepancy in our understanding of forestry effects could be explained by social factors influencing how Canada Warblers choose where to live.

Just as you might choose a neighborhood based on criteria like access to green space, birds also assess their physical environment when choosing where to live. These species-habitat relationships help biologists understand which areas to protect.

But the physical environment is far from the only cue birds use to choose a place to live, nor is it the only cue we use to understand why they live where they do. Just as you might rely on friends’ opinions of a neighborhood to snatch up a good place before it’s off the market, birds may choose to live near members of their own species. If another bird picks an area, chances are it has high quality food, nesting areas, and mates. However, if everybody makes the same decision, problems can arise as they pack into the same location. When habitat is disturbed, choosing to live near neighbors can result in overcrowding in the remaining undisturbed areas and potentially force some birds into the outskirts of high-quality neighborhoods.

After returning from a long spring migration, Canada Warblers have limited time to find a breeding site (they have the shortest breeding season of wood warblers in Alberta!), and strangely, researchers always seem to find Canada Warblers clustered together in some areas while absent from others. Based on this information, we suspected that where Canada Warblers choose to breed might depend on where their neighbors chose to settle. If this is the case, it could explain why they will live in postharvest areas, and in turn, how we perceive the effects of forestry.

Taking quads down muddy trails and bushwhacking through dense shrubbery to our destination, we surveyed for Canada Warblers in boreal Alberta, Canada. We used a recorded song to mimic an intruding male and lure territory owners into our nets. Once captured, we attached color bands to their legs to distinguish between individuals and followed them throughout the breeding season. We documented their space use in and around postharvest areas, how close they were to neighbors, and whether they found a female mate and raised young. See what a day in the life of Canada Warbler biologist looks like here.

Our results showed that numbers of male Canada Warblers were much lower in postharvest areas compared to unharvested forest. The few males that did live partially in postharvest were typically at the edge of nearby unharvested forest. Males were also more likely to live nearer to neighbors rather than spacing out. Hence, Canada Warblers in the boreal forest may not prefer to live in postharvest areas, but may live there as a side effect of trying to be near neighbors in unharvested forest.

But are Canada Warblers reaping the benefits of living near neighbors, or are they feeling the pressure to keep up with the Joneses? We found males living in areas with more neighbors were more likely to be “single” (without a female mate) than males living in areas with fewer neighbors. Overcrowding may lead to increased male-male competition for limited females. These rivalries also mean that males have to spend more time and energy defending their territory, leaving less time and energy to court females.

Our results suggest that protecting large stretches of unharvested forest near sites occupied by Canada Warblers will be important to provide enough habitat and prevent crowding effects. It also goes to show that appearances can be deceiving when it comes to the use of disturbed habitat and that the influence of social behavior should not be underestimated.

Follow Anjolene on Twitter: twitter.com/AnjoleneHunt


AUTHOR BLOG: Geolocator Effects May Have More to Do with Marking Method Than Mass

Wed, 10/18/2017 - 15:58

Henry Streby

Linked paper: Comment on ‘‘Mixed effects of geolocators on reproduction and survival of Cerulean Warblers, a canopy-dwelling, long-distance migrant’’ by H.M. Streby and G.R. Kramer, The Condor: Ornithological Applications 119:4, November 2017.

Unprecedented numbers of species and individual birds have been marked with all sorts of tracking devices in recent years, and those numbers will continue to rise in the future. The data ornithologists are gathering by marking birds with tracking devices are providing a wealth of previously elusive knowledge about all stages of birds’ life cycles. The rapidity with which new tracking studies are being initiated places an ever-growing burden on the USGS Bird Banding Lab (BBL) and other agencies charged with assessing auxiliary marker requests and determining permission to mark birds on a case-by-case basis. In many cases, those agencies have little to no species-specific information on which to base their decisions, either because a species has never been marked before or because those who marked them did not study or did not report marker effects during the course of their research. We as research biologists have an ethical responsibility to objectively assess the potential effects of our research activities on the animals we study for the sake of minimizing harm to the animals and potential bias in our data caused by markers impacting animal behavior or survival.

We applaud the authors of Raybuck et al. (2017) for honoring a request from the BBL to band additional birds as control groups during their geolocator study of Cerulean Warblers. We believe Raybuck et al. conducted their study and published their paper with ethical and admirable intentions and it was not our intention to criticize the integrity of their research. However, their conclusion of an overall geolocator effect on annual survival of Cerulean Warblers was overreaching in light of the modest sample-sizes and the confounding factors of year, site, and marking method. We believe our analysis and interpretation of their apparent annual survival data is more appropriate and clarifies some small but critical shortcomings in their assessment. Of primary concern, the negative geolocator effect on annual survival of Cerulean Warblers was driven by a strong negative effect associated with one marking method in one year, and there was no support for a negative effect of geolocators when they used a different marking method in the second year of their study. This difference was not driven by geolocator mass, because the reduced survival occurred in the year when a lighter geolocator was used.

In our opinion, there are two broad take-home messages from our paper. First, when marking a species for the first time, it is critical to use available knowledge and replicate methods known to work well in closely related species. When the smallest details are considered, there are almost as many methods for deploying a geolocator on a songbird as there are species that have been marked with geolocators. It should not be necessary for each research group to reinvent methods and relearn unfortunate lessons when simple, safe, and effective methods have been developed and made widely available. Second, there is only one control group that is relevant for comparison to a marked group of birds during a geolocator study or any other study of marked birds: a control group identified at the same site(s) during the same period of the same year. Parameters of interest, especially survival, can vary widely among years and populations. It is therefore not appropriate to compare parameters like survival of geolocator-marked birds with those of control birds from any other population or year or even long-term averages from the same population. Just as we have a responsibility to assess the potential effects of our research on the animals we mark, so too do we have a responsibility to design and present those assessments in a statistically rigorous and scientifically appropriate manner. It is then that we achieve our goal of providing accurate information that may be useful to other researchers and those in oversight positions who use this type of information to decide whether continued or new research is permissible.


AUTHOR BLOG: To the Grasshopper Sparrow, the Grass May Be Greener on the Other Side

Wed, 10/11/2017 - 15:39

Emily Williams

Linked paper: Patterns and correlates of within-season breeding dispersal: A common strategy in a declining grassland songbird by E.J. Williams and W.A. Boyle, The Auk: Ornithological Advances 135:1, January 2018.

SY-GD, or silver-yellow, green-dark blue, is a male fiercely defending his territory on his favored signpost perch. Photo credit: D. Rintoul

Late in the summer of 2013, when Alice Boyle, a new faculty member at Kansas State University, was embarking on studies of grassland birds at the Konza Prairie Biological Station in northeastern Kansas, she noticed something really curious: Individual Grasshopper Sparrows she had color-banded earlier in the season were suddenly popping up in new places, singing their hearts out in locations far from where they were originally captured. Whether this was a weird one-off or a predictable and common behavior of grassland birds, Boyle didn’t know.

I started at Kansas State University as Alice’s first graduate student the next fall. She told me the story of the Grasshopper Sparrows and the strange things they did over the summer. With my fondness for movement ecology and a taste for novelty, I opted to base my master’s thesis on the rogue Grasshopper Sparrows seeking greener pastures.

To rewind a little bit, I should explain why this kind of behavior was surprising. The Grasshopper Sparrow is a small, grassland-obligate migratory songbird that spends its winters along the Gulf Coast and Northern Mexico and travels to the Great Plains to spend its summers. Migration is energetically costly, requiring a lot of time and preparation. Once birds arrive at breeding grounds, they have a relatively short window of time to set up a territory, find a mate, build a nest, raise young, and feed fledglings, and then undergo molt, feed, and prepare for the long journey back to the wintering grounds. All of this has to be accomplished in a span of a few short months. Given the constraints of time, resources, and energy, you’d think that they would stick pretty close to their original territory for the whole breeding season. That is what most migrant birds do, after all. The fact that Grasshopper Sparrows would switch territories, duplicating their efforts of setting up another territory, finding a potential new mate, and trying to nest again—it seems like it wouldn’t be worth it. The fact that Grasshopper Sparrows are indeed doing this—changing territories once, twice, maybe three times, even—makes them apparently unusual compared to their migratory counterparts and begs the question, why go to all that effort?!

Before we could examine why Grasshopper Sparrows move around during the breeding season, we first needed to determine just how common this kind of behavior was. We also wanted to find out the distances over which they traveled, where were the new places they chose to settle, and how frequently they moved locations. Following that initial season in 2013, we set out to answer these questions and looked for this behavior in full force. In the next three seasons of field work, we banded 779 Grasshopper Sparrows, outfitted 19 individuals with radio-transmitters to follow their movements, and searched for color banded birds throughout our study area every week to keep track of territory holders and their whereabouts throughout the season.

What we found, we couldn’t have predicted: Within-season breeding dispersal behavior in Grasshopper Sparrows was way more common than we expected. Depending on which of the different metrics we calculated, between 33% and 75% of males disperse at least once within a single breeding season. The scale of movement between territory locations was also remarkable; one individual moved 9 km between breeding attempts—a movement considered pretty large to a bird that defends an average territory size of 43 meters in diameter! If we had not been systematically looking for this behavior, we might have easily missed it; in many areas, densities of Grasshopper Sparrows remained constant throughout the breeding season, but the identities of territory holders changed, sometimes more than once over the summer.

The fact that these birds are moving around a lot during the breeding season introduces its own list of new questions. Now that we detailed the patterns of this behavior, we could begin to answer the questions of why. Why do they do this? What determines why some leave, and some stay? And what determines where they settle next? Could this be a common strategy of other birds occupying similar habitats?  While trying to determine whether this movement was truly unusual by digging into the literature, I actually found quite a bit of evidence for such movements. While the terminology is not consistent, it seems that within-season breeding dispersal could be more common in grassland birds than elsewhere.

The answers to some of these questions formed the rest of my MS research, and some remain as ones we are still working on. But now that the first piece of the puzzle is in place, the next steps are to explore the evolutionary and ecological causes of within-season breeding dispersal in such an interesting little brown job.

To find out more regarding this Grasshopper Sparrow movement story, visit aliceboyle.net and follow us on social media.

Emily on Twitter: twitter.com/wayfaringwilly

Alice on Twitter: twitter.com/birdfiddler

Youtube channel: youtube.com/channel/UCiQiNb9syQ5F455XielMjDA

Flickr: flickr.com/photos/141805443@N08/


Grassland Sparrows Constantly Searching for a Nicer Home

Wed, 10/11/2017 - 15:39

A Grasshopper Sparrow with a radio transmitter. Photo credit: E. Williams

Some birds regularly move to new territories between years, depending on factors including habitat quality and the presence of predators, but what about within a single breeding season? Grassland ecosystems are particularly dynamic, continuously shaped by fire and grazing, and a new study from The Auk: Ornithological Advances confirms that one particular grassland bird moves frequently each summer in search of the best territories. For Grasshopper Sparrows, the grass really does look greener on the other side.

Emily Williams and Alice Boyle of Kansas State University captured 647 male Grasshopper Sparrows over the course of three breeding seasons and marked them with identifying color bands, surveying territories weekly to track their movements. The results indicate that about 75% of males changed territories at least once per season, with a third of banded defending new territories at least 100 meters away from where they were originally sighted. Additionally, 9 of 19 birds fitted with radio transmitters established new territories as far as 1200 meters away from their original locations.

“We had many plots where the density remained relatively stable over the entire breeding season, which could appear as if individual birds remained settled in the same areas over time. However, what we found was the complete opposite—individuals were blinking in and out of territories the entire time,” says Williams, who has since moved on to a position at Denali National Park and Preserve. “So while an onlooker could see a male Grasshopper Sparrow singing on a single patch of ironweed for months at a time, the identity of the individual claiming that ironweed as his own could change two or three times in a single summer.” Without careful observations, researchers could completely miss these dynamic movements happening over the course of a season.

This high turnover implies that while some birds might perceive a patch of habitat as no longer suitable, others see the same area as a good place to settle, perhaps because they base decisions on their individual experiences of nest success or failure. High mobility may benefit grassland birds by helping them locate isolated patches of high-quality habitat and colonize newly created or restored habitat, but could also challenge researchers’ ability to accurately track survival over time.

“Many avian ecologists have probably anecdotally noticed within-season shifts in breeding territories, yet this is one of the first attempts to actually quantify this phenomenon. The extent to which territorial turnover occurred and the fairly extensive distances moved by males within a season are intriguing!” says the University of Wyoming’s Anna Chalfoun, an expert on grassland birds who was not involved in the study. “I am left wondering if this behavior is more common than ornithologists have previously acknowledged and what drives proximate shifts in breeding territories. The results certainly have implications for habitat management for territorial birds of concern and for the accuracy of survival and site fidelity analyses.”

Patterns and correlates of within-season breeding dispersal: A common strategy in a declining grassland songbird is available at http://www.bioone.org/doi/full/10.1642/AUK-17-69.1.

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.


Safety, Not Food, Entices Geese to Cities

Wed, 10/11/2017 - 09:06

Radio transmitter data has revealed the real reason geese hang out in cities. Photo credit: M. Horath

Canada Geese have shifted their winter range northward in recent years by taking advantage of conditions in urban areas—but what specific features of cities make this possible? A new study from The Condor: Ornithological Applications suggests that rather than food, geese are seeking safety, congregating in areas where they can avoid hunters and be buffered from the coldest winter temperatures.

Heath Hagy of the University of Illinois at Urbana–Champaign and his colleagues captured 41 geese in the Greater Chicago Metropolitan Area between 2014 and 2016 and fitted them with radio transmitters to track their movements. While the geese used a remarkable variety of urban habitats, they preferred deep water and rivers over green space such as parks when temperatures dropped enough to tax their ability to maintain their body temperature. For geese that remained within the metropolitan area, winter survival was 100%, but this dropped to 48% for those that emigrated out to forage in surrounding agricultural fields, countering expectations that the proximity of agricultural habitat may be a factor in geese’s winter expansion in the area. Together, these results suggest that sanctuary may be a higher priority for wintering geese than good foraging habitat.

Better understanding how geese use urban habitat in winter may help reduce human–wildlife conflicts such as collisions with airplanes. “The growth of urban areas and northward expansion of row-crop agriculture have changed the way geese migrate. Unfortunately, some of our large cities have become goose sanctuaries, where resident geese and migratory geese congregate during winter to escape hunting pressure,” says Hagy. “Although additional research is needed, our data will be useful to guide goose harassment efforts, which may offset the benefits of remaining inside urban areas during winter and open hunting seasons.”

“This work offers comprehensive insights into the biology and behavior of a large wintering population of Canada geese that inhabits a major metropolitan area in the mid-western U.S. Appropriately grounded in an energetic context, the study thoroughly describes how Canada geese utilize the urban environment under varying weather conditions and demonstrates the survival benefits of urban adaptation,” according to The Ohio State University’s Robert Gates, a wildlife management expert who was not involved in the research. “Findings from this study provide a firm biological grounding for the development and implementation of management actions to alleviate human–Canada goose conflicts in urban areas.”

Survival and habitat selection of Canada Geese during autumn and winter in metropolitan Chicago, USA is available at http://www.bioone.org/doi/abs/10.1650/CONDOR-16-234.1.

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. The Condor had the top impact factor among ornithology journals for 2016.


AUTHOR BLOG: Flooding, Predators, and an Imperiled Sparrow

Wed, 09/27/2017 - 12:20

A banded adult Saltmarsh Sparrow female foraging in Scarborough, ME. Photo credit: D. Hitchcox

Kate Ruskin

Linked paper: Demographic analysis demonstrates systematic but independent spatial variation in abiotic and biotic stressors across 59 percent of a global species range by K.J. Ruskin, M.A. Etterson, T.P. Hodgman, A.C. Borowske, J.B. Cohen, C.S. Elphick, C.R. Field, R.A. Longenecker, E. King, A.R. Kocek, A.I. Kovach, K.M. O’Brien, N. Pau, W.G. Shriver, J. Walsh, and B.J. Olsen, The Auk: Ornithological Advances 119:4, October 2017.

Ecologists have long hypothesized that the factors that affect a species vary over its geographical range. For example, cold climates may limit survival at higher latitudes, while competition with other species may be more important at lower latitudes. Scientists have proposed that this sets up a tradeoff for each species, favoring individuals that are physiologically hearty to harsh abiotic conditions at higher latitudes and individuals that are good competitors at lower latitudes.

With the help of 14 coauthors scattered across the northeastern U.S., I collected demographic data on Saltmarsh Sparrows to test whether this pattern was supported. Our team, known as the Saltmarsh Habitat and Avian Research Program (SHARP), conducted coordinated demographic research on Saltmarsh Sparrows at 23 sites in 7 states from Maine to New Jersey. We searched for nests, revisited them every few days throughout the breeding season, and classified each as successful or failed due to various causes.

Saltmarsh Sparrows breed exclusively in high marsh habitat, which is the zone of tidal marshes that typically floods monthly during the astronomical high tides. Saltmarsh Sparrows build their nests in the short grasses of the tidal marsh, just a few inches above the ground. As a result, nests often fail due to flooding during the high monthly tides. Most nest failure in Saltmarsh Sparrows is caused either by this nest flooding, or by depredation.

Using monitoring records from 837 nests collected across our study sites, we observed patterns in the factors that limit nest survival that varied predictably across hundreds of kilometers. We found that the biotic stressor, nest depredation, increased toward lower latitudes, which is consistent with the Asymmetric Abiotic Stress Limitation (AASL) hypothesis. AASL proposes that populations are limited by biotic stressors like nest depredation at the lower latitudes of their range, while abiotic stressors such as climate limit populations at higher latitudes. Conversely, we observed that the abiotic stressor, nest flooding, did not vary with latitude. Instead, nest flooding was best predicted by indicators for regular monthly flooding as well as irregular flooding events, which varied independent of latitude. Our results suggest that stressors to Saltmarsh Sparrow reproductive success vary systematically across its range, but independently from each other. Therefore, we did not observe the tradeoff between physiological heartiness at higher latitudes and competitiveness at lower latitudes that is predicted by the AASL hypothesis.

In addition to the insight this example provides into how different stressors limit species across their ranges, the patterns of biotic and abiotic stress that we observed provide information relevant to conservation of the Saltmarsh Sparrow. The Saltmarsh Sparrow is considered threatened by the International Union for the Conservation of Nature, and SHARP researchers have found that the Saltmarsh Sparrow population is small, declining, and expected to go extinct this century. For example, our results suggest that predator control may be an effective method for improving Saltmarsh Sparrow fecundity toward the low latitudes of its range, but not farther north.

This new article in Auk: Ornithological Advances is the latest in a series we have written about the Saltmarsh Sparrow and other tidal marsh birds found in northeastern North America, many of which are facing population declines and habitat change. Learn more about tidal marsh birds and SHARP’s research at our website (www.tidalmarshbirds.org) and Facebook page (www.facebook.com/tidalmarshbirds).


Songbird Populations May Indicate Trouble in Northwestern Forests

Wed, 09/27/2017 - 10:37

Purple Finches, an indicator of healthy coniferous habitat, are declining in the Northwest. Photo credit: J. Livaudais

Populations of many North American songbirds are declining, and in many cases we don’t understand why—for example, whether the problem lies with reproductive success or in the survival rates of adults. Conservation efforts need this information to be effective, and bird banding stations can help fill in the gaps, providing insights into how demographics vary across space and time. A new study from The Condor: Ornithological Applications presents ten years of data from banding stations across northern California and southern Oregon and offers new hints on what’s driving changes in the region’s songbird populations.

The Klamath Bird Observatory’s Sarah Rockwell and her colleagues used data collected at ten of the observatory’s bird banding sites between 2002 and 2013 to estimate the abundance and reproductive productivity of twelve songbird species, all either of regional conservation concern or indicators of coniferous or riparian habitat quality. They found that three species (the Purple Finch, Yellow-rumped Warbler, and Dark-eyed Junco), all indicators of coniferous habitat, were declining across the region, while two (the Yellow-breasted Chat and Black-headed Grosbeak) were increasing, though the trends varied from site to site. While breeding productivity declined in three species, adult abundance was correlated with the previous year’s productivity for only one species, the Yellow Warbler, suggesting that local productivity is not the primary culprit behind population declines.

“Before we can understand the impact of threats to bird populations, we first need to understand what’s happening where,” says John Alexander, the Executive Director of the Klamath Bird Observatory and a coauthor on the work. “This study presents trends from regional-scale monitoring and just begins to scratch the surface of understanding population dynamics, variation in demographic rates, and drivers of population change across our landscape, which is vital information for developing effective conservation plans. It also highlights concerns about forest-associated species in this region—the need to balance timber harvest, a mixed-severity fire regime, and endangered species management continue to present complex conservation challenges.”

“We have been so lucky to consistently get awesome field crews—we host six to ten interns each year, and they travel all over the Klamath-Siskiyou bioregion, camping regularly throughout the field season. We have had interns from more than seventeen different countries, and they all receive extensive training and work very hard,” adds Rockwell. “This work is so important. We need robust baseline data if we are going to be aware of any kind of population change, let alone be able to do something about it!”

Spatial variation in songbird demographic trends from a regional network of banding stations in the Pacific Northwest is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-44.1.

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, 2.654.

About Klamath Bird Observatory: Based in Ashland, Oregon, KBO is a scientific non-profit organization that achieves bird conservation in the Pacific Northwest and throughout the migratory ranges of the birds of our region. Emphasizing high caliber science and the role of birds as indicators of the health of the land, KBO specializes in cost-effective bird monitoring and research projects that improve natural resource management. Also, recognizing that conservation occurs across many fronts, we nurture a conservation ethic in our communities through our outreach and educational programs.


A First Look at Geographic Variation in Gentoo Penguin Calls

Wed, 09/27/2017 - 09:56

A calling Gentoo Penguin. Photo credit: M. Lynch

Vocal communication is central to the lives of many birds, which use sound to attract mates and defend territories. Penguins are no exception, but we know little about how or why penguin vocalizations vary geographically between isolated populations. A new study from The Auk: Ornithological Advances takes a broad look at vocalizations across the range of Gentoo Penguins and concludes that while their calls do vary from place to place, we still have a lot to learn about the processes at work.

The Gentoo Penguin’s “ecstatic” call, consisting of repeated pairs of short syllables, is used to attract and contact mates. Maureen Lynch and her PhD advisor Dr. Heather Lynch (no relation) of Stony Brook University recorded ecstatic calls at 22 Gentoo Penguin colonies across the Antarctic Peninsula, southern Argentina, and nearby islands. While they found variation in call frequency and duration both within and between colonies, no clear patterns emerged based on latitude, region, or subspecies. An algorithm based on their data was able to classify calls to correct colonies better than random, but with a high error rate.

Their results suggest that the vocal characteristics of colonies drift independently of each other over time. Within colonies, it may be beneficial for individuals to differ in their calls so that they can tell each other apart. “There is so much that we still do not know about penguin vocal behavior,” says Heather. “We see this as being very much the beginning, rather than the end, of understanding how penguins communicate, how and if such communications play a functional role in protection against predators, choice of mates, and breeding site selection.”

“Work in the Antarctic is always challenging, and this project was time- and data-intensive, with data collection over three field seasons,” adds Maureen. “Unexpected challenges came from flying birds rather than penguins. The recording units hold up well in the Antarctic elements and can even record over winter, but I learned the hard way that if I leave a Song Meter unattended in the Falkland Islands, the Striated Caracaras will eat the windscreens off the microphones and can actually pull the microphones off.”

“Understanding the drivers of population differentiation is increasingly important for species such as penguins that are being impacted by climate change,” according to Fordham University’s J. Alan Clark, a penguin behavior researcher who was not involved in the study. “This study, the largest of its kind, takes a creative and rigorous approach to exploring the role of vocalizations in population differentiation across a wide geographic range and across populations with known intraspecific genetic variation. The results of this study provide practical insights that help set the stage for future research on interactions between speciation processes and climate change.”

Variation in the ecstatic display call of the Gentoo Penguin (Pygoscelis papua) across regional geographic scales is available at http://www.bioone.org/doi/full/10.1642/AUK-17-4.1.

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.


Could Condors Return to Northern California?

Wed, 09/20/2017 - 09:27

A study of lead exposure indicates condors could one day return to Northern California. Image credit: C. West

In 2003, Northern California’s Yurok Tribe initiated efforts to reintroduce California Condors on their lands. While wild condors have not existed in the region for more than a hundred years, a new study from The Condor: Ornithological Applications suggests that hunters transitioning from lead to non-lead ammunition may allow these apex scavengers to succeed there once again.

Lead, which condors consume when scavenging at carcasses of animals killed with lead ammunition, is the main factor limiting their recovery; lead toxicosis was responsible for 26% of juvenile condor deaths and 67% of adult condor deaths between 1992 and 2009. To assess condor’s prospects in Northern California, Chris West of the Yurok Tribe Wildlife Program and his colleagues trapped two other avian scavengers, Turkey Vultures and Common Ravens, at nine sites in the region between 2009 and 2013. Collecting blood samples from 137 vultures and 27 ravens, they found that lead levels in ravens were almost six times higher during hunting season, when they were exposed to animal remains tainted with lead ammunition, than the rest of the year. Vulture’s migratory movements meant they couldn’t be sampled across seasons, but older vultures tended to have higher concentrations of lead, suggesting that older, more dominant individuals exclude younger birds from foraging on carcasses.

While this may sound like bad news, it means little stands in the way of condor recovery if hunters shift away from using lead ammunition in the region. A statewide ban on lead ammunition in California takes effect in 2019, and West and his colleagues are optimistic that it may lower lead exposure to scavengers if it includes outreach programs to help the state’s hunting community through the transition. “Our hopes for condor reintroduction to our area and recovery overall is very high. We are currently going through the National Environmental Policy Act (NEPA) process to select release locations and assess and mitigate impacts to land owners and managers in the region,” says West. “The return of condors to the Pacific Northwest, after more than a century-long absence, will be a testament to the ability of federal, tribal, state, and private entities to come together to champion the cause of wildlife, ecosystem, and cultural recovery in our region.”

“Northern California still has viable habitat for free-flying California Condors, and these results suggest it is possible to succeed in this region, particularly as a broader switch from lead to non-lead ammunition use is realized,” adds to Kelly Sorenson, Executive Director of the Ventana Wildlife Society and an expert on condor recovery who was not involved in the study. “If we fix the lead problem, condors should survive in the wild again without the assistance of people, whether in Northern California or other suitable locations where they are being released.”

Feasibility of California Condor recovery in northern California, USA: Contaminants in surrogate Turkey Vultures and Common Ravens is available at http://www.bioone.org/doi/abs/10.1650/CONDOR-17-48.1.

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. The Condor had the top impact factor among ornithology journals for 2016.


Social Environment Matters for Duck Penis Size

Wed, 09/20/2017 - 09:25

Penis size in Ruddy Ducks has a complex relationship with the birds’ social environment. Image credit: P. Brennan

Most birds lack genitalia, but male ducks are known for their long, spiraling penises, which have evolved through an ongoing cat-and-mouse game with females. A new study from The Auk: Ornithological Advances looks at whether these impressive organs are affected by the social environment—that is, whether male ducks that face more competition grow bigger penises. While this appears to be true for some species, in others the relationship between social environment and penis growth is more complex.

Patricia Brennan of Mount Holyoke College and her colleagues tested their hypothesis in two species: Ruddy Ducks, which are very promiscuous, do not form pair bonds, and have relatively long penises, and Lesser Scaup, which form seasonal pair bonds and have relatively short penises. Keeping captive ducks in either pairs or groups during the breeding season over two years, they found that Lesser Scaup had longer penises on average when housed in groups with other males, as predicted. For Ruddy Ducks, the effects were more complicated—many males failed to reach sexual maturity until the second year of the experiment, and when they did, the smaller Ruddy Duck males housed in groups grew their penises faster than males housed in pairs, but grew out of sync with each other and stayed in reproductive condition for only short periods of time.

Small Ruddy Ducks males faced with intense competition may strategically offset their development from each other to reduce the costs of male–male aggression and make the best of a bad situation. Additionally, since Ruddy Ducks already have relatively long penises on average compared to other waterfowl species, their ability to grow even larger based on social cues may be limited. In any case, the study shows that the level of competition that individual male ducks experience can have a big effect on their genitals.

The biggest challenge during the study, says Brennan, wasn’t measuring the ducks—it was simply keeping them housed and fed. “Keeping ducks in captivity is expensive,” says Brennan. “We were lucky to partner with the Livingstone Ripley Waterfowl Conservancy in Litchfield, Connecticut, where their expert personnel kept the ducks healthy and in beautiful, naturalistic enclosures year-round.”

“This is an excellent experimental study of penis morphology, looking at the effects of social environment on penis size in two duck species that have different mating systems,” according to Queen’s University’s Bob Montgomerie, an expert on reproductive strategies who was not involved in the study. “The question now is whether the observed increase in penis size in Lesser Scaup under the threat of sperm competition actually gives males a competitive advantage. Like all good studies, this one will undoubtedly stimulate more research, as it provides both methodologies and a clear focus on interesting questions.”

Evidence of phenotypic plasticity of penis morphology and delayed reproductive maturation in response to male competition in waterfowl is available at http://www.bioone.org/doi/full/10.1642/AUK-17-114.1.

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.


Song Experiments Reveal 21 Possible New Tropical Bird Species

Wed, 09/13/2017 - 10:05

Playback studies indicate that two populations of Buff-throated Foliage-gleaners do not recognize each other’s songs. Photo credit: B. Freeman

Birds often choose their mates based on song, making it a key factor in separating species. However, analyzing spectrograms can only tell us so much—the characteristics that birds hone in on when identifying potential mates may not be the same ones scientists notice in audio recordings. A new study from The Auk: Ornithological Advances uses field experiments to “ask the birds themselves” and uncovers as many as 21 previously unrecognized species.

Benjamin Freeman of the University of British Columbia and Graham Montgomery of Cornell University compared these two methods—analysis in the lab and experiments in the field—for 72 pairs of related but geographically separated bird populations in Costa Rica, Panama, and Ecuador. In addition to analyzing more than a thousand song recordings for seven variables, they used playback experiments to test birds’ real-world reactions to recordings of their relatives, observing whether or not they approached the speaker. Their results show that when the divergence between the characteristics of the recordings is high, birds consistently fail to recognize recordings of their relatives in the field, but when divergence is low, birds’ discrimination is much less consistent. In other words, analyzing recordings can’t accurately predict how birds will act when presented with songs just slightly different from their own.

Many pairs that failed to recognize each other are currently categorized as members of the same species, suggesting that current taxonomy does not reflect actual bird behavior when it comes to song. Freeman and Montgomery propose that 21 such pairs should be recognized as separate species based on song discrimination and that playback experiments should be the standard for assessing whether song divergence between populations is a barrier to interbreeding. “It is abundantly clear to anyone familiar with the amazing diversity of Neotropical birds that there are many cases where populations that sing very different songs are classified as the same species,” says Freeman. “These populations look the same—they have similar plumage and are similar in size and shape—but assuming that populations that sing differently tend not to interbreed, this means that species-level diversity in the Neotropics is underestimated.”

“Playback experiments between geographically isolated taxa provide key data on how populations might perceive each other in terms of ‘same’ or ‘different’ if they were in actual contact,” according to Louisiana State University’s J.V. Remsen, an expert on Neotropical birds who was not involved in the research. “Hopefully, this pioneering study will catalyze a wave of similar studies around the globe as a way to approach the always-thorny problem of species limits in these birds.”

Using song playback experiments to measure species recognition between geographically isolated populations: A comparison with acoustic trait analyses is available at http://www.bioone.org/doi/full/10.1642/AUK-17-63.1.

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.


Will Mallards Hybridize Their Cousins out of Existence?

Wed, 09/06/2017 - 09:49

Mallards may threaten their relatives’ genetic distinctiveness through hybridization. Photo credit: Gary Kramer, USFWS (public domain)

Mallards—the familiar green-headed ducks of city parks—are one of a group of closely related waterfowl species, many of which are far less common. Interbreeding with Mallards can threaten the genetic distinctiveness of those other species and cause concern for their conservation. A new study from The Condor: Ornithological Applications investigates hybridization between Mallards and Mottled Ducks, a species specially adapted for life in Gulf Coast marshes, and finds that while hybridization rates are currently low, human activity could cause them to rise in the future.

In Florida, hybridization between domesticated Mallards and Mottled Ducks is a cause for concern, but the degree of hybridization in the western Gulf Coast region is less well known. Louisiana State University’s Robert Ford and his colleagues took blood samples from Mottled Ducks captured on the coast of Louisiana in 2011–2014, supplementing them with samples from Mottled Ducks and Mallards from Texas, Alabama, and Mississippi. Analyzing the birds’ DNA, they found that the hybridization rate in the western Gulf Coast region is currently only 5–8%, a level lower than what’s been documented in Florida. However, that doesn’t mean the western Gulf population is completely in the clear.

Currently, the two species have little opportunity to interact in the region during the breeding season; Mottled Ducks nest in coastal marshes, while most Mallards are migratory and breed outside the region. However, the ongoing loss of marsh habitat could cause Mottled Ducks to move into urban and suburban areas, where they will be more likely to encounter resident Mallards. To prevent future problems, Ford and his colleagues recommend ongoing monitoring of hybridization in the region and better protection of coastal marsh habitat.

“The biggest challenge in collecting samples was finding molting Mottled Ducks, which we collected during bird banding operations in the summer. Identifying birds as either Mottled Ducks or Mallards in the summer can be difficult, but most of our banders had years of experience and we did not have many problems,” says Ford. “In the future, I would like to see improvements in the methods to identify hybrids, such as more precise techniques that could identify gene combinations unique to hybrids.”

“Hybridization between Mottled Ducks and Mallards is a significant conservation concern in the southern U.S.,” according to waterfowl expert and Auburn University emeritus professor Gary Hepp, who was not involved in the study. “Ford et al. recommend programs to monitor future changes in hybridization, and a proactive management approach similar to Florida’s that controls the number of non-migratory Mallards while prohibiting future releases of game farm Mallards may also be prudent.”

Hybridization between Mottled Ducks (Anas fulvigula maculosa) and Mallards (A. platyrhynchos) in the western Gulf Coast region is available at http://www.bioone.org/doi/abs/10.1650/CONDOR-17-18.1.

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.


Some Birds Better Than Others at Adjusting to Habitat Degradation

Wed, 08/30/2017 - 09:44

Rufous-collared Sparrows are among the birds able to switch their diet between seed types as habitats change. Photo credit: M.C. Sagario

Before habitat degradation from impacts like grazing begins to cause population declines, the first response by wildlife usually comes in the form of behavioral changes—for example, switching their diets in response to changes in food availability. A new study from The Condor: Ornithological Applications looks at the diets of seed-eating birds in a South American desert and finds that while some can switch between seed types when grazing alters local plant communities, others continue to stick to old favorites, limiting their options.

Luis Marone of the Argentine Arid Zones Research Institute (IADIZA-CONICET) and his colleagues collected soil samples at grazed and ungrazed sites in Argentina’s Monte Desert to assess the composition of the seed bank in each area, finding fewer of the large grass seeds that birds prefer in the grazed areas. Flushing the digestive tracts of captured birds revealed that two seed generalists, Common Diuca-Finch and Rufous-collared Sparrow, adjusted their diet accordingly and ate more forb seeds at grazed sites, while grass seed specialists Many-colored Chaco Finch and Ringed Warbling-Finch did not.

Studies like this one could enable us to predict which species will be most vulnerable to population declines due to habitat changes, as the inflexible specialist species are more likely to suffer when they can’t find enough of their preferred food. “Given that cattle breeders usually sow grass species as fodder, our results should be used for managing cattle stocks with bird conservation in mind by selecting the fodder species that are most consumed by the most specialized seed-eating birds,” says Marone. “This kind of management could help prevent reductions of bird abundance in grazed areas.”

“Although birds in this study were shown to compensate by switching to other seed types, the findings suggest that the capacity of grazed lands to support similar numbers of birds as ungrazed lands may be compromised,” according to the Vermont Center for Ecostudies’ Rosalind Renfrew, an expert on grassland bird conservation who was not involved in the study. “Grazed lands play a major, essential role in grassland bird conservation in South America, and this important research reveals that specialized birds may be limited by habitat quality. The findings underscore the need for a diverse approach to grassland bird conservation in Argentina that considers quality as well as area.”

Diet switching of seed-eating birds wintering in grazed habitats of the central Monte Desert, Argentina is available at http://www.bioone.org/doi/abs/10.1650/CONDOR-17-61.1.

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.


AUTHOR BLOG: Not Too Many Sperm, Not Too Few

Wed, 08/16/2017 - 10:03

Male Zebra Finch and Long-tailed Finch. Photo credit: L. Hurley

 

Laura Hurley

Linked paper: Variation in the number of sperm trapped on the perivitelline layer of the egg in three species of estrildid finch by L.L. Hurley, K.V. Fanson, and S.C. Griffith, The Auk: Ornithological Advances 119:4, October 2017.

When you crack open your morning egg, you see the familiar yolk with its little white circle staring at you. That little white circle, the germinal disk, is the target sperm are aiming for to fertilize the big yolky ovum, but in birds one sperm is not enough to turn the egg into a chick. Multiple sperm must fuse with the ovum for this to happen, so lots of sperm are present at fertilization, and those that don’t fuse can become trapped between the two delicate layers that surround the yolk.

Hope I didn’t ruin breakfast for you. However, too many sperm reaching the egg can cause the development of the chick to fail, so there’s a bit of a Goldilocks situation—just the just right number of sperm are needed. The size of bird eggs vary widely—from hummingbirds to emus—and so does the number of sperm that reach their ovum. In general, the number of sperm varies with body size, but there is a lot of unexplained variation between species of similar size, within species, and even within a clutch of eggs. In our current paper, we explore variation in three similarly sized birds from a family of Australian finches to help us better hypothesize about what could be influencing sperm numbers.

This is part of a larger body of avian ecology work looking at how genetic, social, and environmental factors influence and regulate reproduction, development, and population dynamics (https://griffithecology.com). This work involves a number of Australian species in both wild and captive settings, including Gouldian Finch, Zebra Finch, Long-tailed Finch, and Chestnut-crowned Babbler, as well as the invasive House Sparrow. We also use historical records to build models to help us understand the life history of birds across the whole of Australia—for example, opportunistic breeding (https://doi.org/10.1642/AUK-16-243.1) and nest structure (https://doi.org/10.1098/rspb.2016.2708).


Prairie-Chicken Nests Appear Unaffected by Wind Energy Facility

Wed, 08/09/2017 - 14:22

Prairie chickens nests appear unaffected by the proximity of a small wind energy facility. Photo credit: L. Powell

Wind energy development in the Great Plains is increasing, spurring concern about its potential effects on grassland birds, the most rapidly declining avian group in North America. However, a new study from The Condor: Ornithological Applications suggests that for one grassland bird species of concern—the Greater Prairie-Chicken—wind energy infrastructure has little to no effect on nesting. Instead, roads and livestock grazing remain the most significant threats to its successful reproduction.

Prairie-chickens are thought to avoid tall structures such as wind turbines because they provide a perch from which raptors can hunt. To learn more, the University of Nebraska–Lincoln’s Jocelyn Olney Harrison and her colleagues gathered data on the effects of an existing small wind energy facility (36 turbines) in Nebraska. They captured 78 female prairie-chickens at breeding sites, or leks, ranging from less than a kilometer from the wind energy facility to more than twenty kilometers away, and fitted the birds with transmitters to track them to their nests. Monitoring their nesting success and collecting data on the habitat characteristics of each nest site, they found little evidence that the wind energy facility affected nest site selection or a nest’s chances of survival. Instead, vegetation characteristics, driven by land use practices such as grazing, had the greatest influence on prairie-chicken nests. Birds also avoided nesting near roads.

“When comparing previous studies to our own, it appears that the effects of wind energy facilities on prairie grouse are often site- and species-specific,” says Harrison. “Therefore, it’s important to consider the results of our study in the context of the size and location of the wind energy facility, as well as the prairie grouse species investigated. We suggest that livestock grazing and other grassland management practices still have the most important regional effects on Greater Prairie-Chickens, but we caution future planners to account for potential negative effects of roads on nest site placement.”

Private landowners were key to completing the study, Harrison adds. “Our radio- and satellite-tagged Greater Prairie-Chickens made larger than expected movements while we were tracking them, which led us to require permission from new land owners on almost a weekly basis during our field seasons. Landowners throughout our field study area were always extremely welcoming and helpful, and genuinely interested in our work. Our project was a success due to more than 50 landowners who granted us access to their private lands.”

Nest site selection and nest survival of Greater Prairie-Chickens near a wind energy facility is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-51.1.

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.


Pages

Welcome to the American Ornithological Society (AOS)
Advancing Scientific Knowledge and Conservation of Birds

© 2017 American Ornithological Society