Birds’ Feathers Reveal Their Winter Diet

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A freshly molted Bobolink. Photo credit: R.M. Jensen

Influences outside the breeding season can matter a lot for the population health of migratory birds, but it’s tough to track what happens once species scatter across South America for the winter months. A study from The Condor: Ornithological Applications tries a new approach for determining what declining migratory grassland birds called Bobolinks eat after they head south for the winter—analyzing the carbon compounds in their plumage, which are determined by the types of plants the birds consume while growing their feathers during their winter molt.

Thanks to a quirk of photosynthesis, rice contains a different ratio of carbon isotopes than most of the native grasses in South America where Bobolinks winter. Rosalind Renfrew of the Vermont Center for Ecostudies and her colleagues took advantage of this, collecting feather samples from wintering Bobolinks in a rice-producing region and a grassland region and from breeding Bobolinks in North America. When they analyzed the feathers’ isotopes ratios, the results from South America confirmed that isotopes in Bobolinks’ feathers reflected the differences in their diets between regions with and without rice production. The samples taken in North America showed that the winter diet of most individuals was weighted more toward non-rice material, but that rice consumption was highest late in the winter, when rice is nearing harvest and the birds are preparing for their northbound migration.

Rice could be beneficial by providing the birds with needed calories as they prepare for their journey north, but it could also increase Bobolinks’ exposure to pesticides and threats from farmers who see them as pests. According to Renfrew and her colleagues, maintaining native grasslands, encouraging integrated pest management programs to reduce toxic pesticide applications, and compensating farmers for crops lost to feeding birds all would be helpful.

“The time spent coordinating the field work for this study may well have been greater than the time spent collecting the data,” says Renfrew. “It was truly a team effort, and the assistance we received from our partners was absolutely essential, especially in South America. Aves Argentinas and the Museo de Historia Natural de Noel Kempff Mercado provided priceless logistical support, and this study could not have happened without them. Some of the same partners have provided input on a Bobolink Conservation Plan that lays out actions to address threats to grassland birds in North and South America, based on results from this and other studies.”

“As Bobolink populations continue to decline, Renfrew and her colleagues use state-of-the-art isotope analysis techniques to assess the Bobolink’s diet on its South American wintering grounds,” according to John McCracken of Bird Studies Canada, an expert on grassland bird conservation who was not involved with the study. “The authors conclude that rice may have negative effects on Bobolinks, owing to its relatively low nutritional quality and from exposure to insecticides.”

Winter diet of Bobolink, a long-distance migratory grassland bird, inferred from feather isotopes is available at http://www.bioone.org/doi/full/10.1650/CONDOR-16-162.1.

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.

2016 Journal Impact Factors Released

The 2016 impact factors for peer-reviewed journals were released last week, and both journals published by the American Ornithological Society saw a boost in their numbers—The Condor is up to 2.654 from 1.427 and is now #1 of the 24 ornithology journals ranked, and The Auk is up to 2.096 from 1.871 (ranking #4). This means that the American Ornithological Society now publishes half of the top four ornithology journals in the world.

Impact factors are calculated based on the number of citations received in a year by articles published in a journal during the two preceding years and are considered to be an important measure of a journal’s prominence in its field. The AOS publications team wants to thank all of our Associate Editors, authors, and reviewers, as well as everyone who reads and cites The Auk and The Condor!

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Muscle Fibers Alone Can’t Explain Sex Differences in Bird Song

Male birds tend to be better singers than females—but does the basis for this difference lie in the brain or in the syrinx, the bird equivalent of our larynx? The researchers behind a new study from The Auk: Ornithological Advances analyzed the muscle fibers in the syrinxes of male and female birds from a range of species and found, to their surprise, that the amount of “superfast” muscle wasn’t typically related to differences in vocal ability between the sexes.

Most muscle fibers are one of two types—fast, specialized for short, intense bursts of activity, or slow, specialized for endurance. However, some animals, including birds, have a third type called superfast muscle that can contract around 200 times per second. Ron Meyers of Weber State University and his colleagues hypothesized that superfast muscle fibers in the syrinx might explain the greater singing ability of male birds, but when they analyzed the syringeal muscles of male and female birds from a range of species, they found that the amount of superfast muscle fiber didn’t differ between the sexes in most species. Instead, their results suggest that the role of superfast muscle is more complicated than they expected and may be related to the entire range of vocalizations of a species rather than song alone. Even though females of some species don’t sing, their superfast muscle fibers appear likely to play a role in the calls they use for other types of communication.

The researchers collected syringeal tissue from a total of ten bird species, some wild-caught and some from a University of Utah aviary. All species had both fast muscle and superfast muscle fiber in their syrinxes, but there was a clear sex difference in fiber type composition in only two species studied, Bengalese Finches and Zebra Finches. Based on this, the researchers speculate that the need for superfast muscle may be related to the entire vocal repertoire of each sex, not just singing behavior. Calls made by Zebra Finch females don’t have acoustic features that would require rapid muscle control, but in other species females may produce calls that require the muscle control provided by superfast fibers even if they don’t sing.

“The data really surprised us,” says Meyers. “Based on our first species studied, starlings and Zebra Finches, we went into this thinking that superfast fibers were related to singing in males. Zebra Finch males sing and females don’t, and males have 85% of the syrinx muscles made up of superfast fibers. In starlings, both male and females sing, and they both had about a 65% make-up of superfast fibers. But as the number of species we looked at grew, we had to totally change our perception of the role of superfast fibers in singing and the role they actually play in vocalizing.”

“Most of the research investigating the mechanisms of bird song focuses on the brain. However, research has begun to suggest that peripheral structures like the syrinx influence song divergence, which of course is an important factor that contributes to avian biodiversity,” according to Wake Forest University’s Matthew Fuxjager, an expert on superfast muscle. “This study therefore provides an exciting starting point to address this issue from a physiological perspective, and it shows that muscle fiber content in the syrinx might not be a strong predictor of avian vocal diversity. But then what is? I would argue that we’re still working this out, and that this study will provide an intriguing framework from which more work in this area can be conducted.”

Is sexual dimorphism in singing behavior related to syringeal muscle composition? is available at http://www.bioone.org/doi/full/10.1642/AUK-17-3.1.

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.

Radar Reveals Steep Declines in Kauai’s Seabird Populations

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A Newell’s Shearwater chick in a burrow. Photo credit: A. Raine

The island of Kauai is home to two endangered seabirds, the Hawaiian Petrel and the Newell’s Shearwater. Monitoring these birds, which are nocturnal and nest in hard-to-access areas, is challenging, but observing the movements of birds via radar offers a solution. A new study from The Condor: Ornithological Applications takes a fresh look at two decades of radar data—and comes to worrying conclusions about the status of both species.

To assess the population trends and distribution of the birds in recent decades, André Raine of the Kauai Endangered Seabird Recovery Project and his colleagues examined past and contemporary radar surveys as well as data on the numbers of shearwater fledglings rescued after being attracted to artificial lights. Their results shows continuing population declines in both species over the last twenty years—a 78% reduction in radar detections for Hawaiian Petrels and a 94% reduction for Newell’s Shearwaters, with the shearwater decline mirrored in decreasing numbers of recovered fledglings over time.

For shearwaters, this is consistent with previously published work, but past analyses of petrel radar data suggested their population was stable or potentially increasing. The researchers attribute the difference to the fact that for this new study, they carefully standardized the data based on sunset times, which ensured that the time periods (and thus bird movement periods) under consideration remained constant from the beginning to the end of the survey period. They believe that the steep declines may have commenced in earnest in the aftermath of Hurricane Iniki in 1992, which led to permanent ecological changes such as the opening of new routes for invasion by exotic predators and plants, as well as significant infrastructure changes across the island.

“These seabirds face a wide range of threats,” says Raine. “Conservation effort needs to be focused on reducing power line collisions, fall-out related to artificial lights, the control of introduced predators, and the overall protection of their breeding habitats. Many of these efforts are now underway on Kauai, and I am hopeful that these will continue and expand over the next few years. Ultimately, the conservation of the breeding grounds of endangered seabirds on Kauai is actually the conservation of our native forests and watersheds, with far-reaching benefits for other native plants and birds that rely on these habitats, as well as—ultimately—ourselves.”

“It is important to publish this information so that everyone can better understand the severity of the declines in these species and the threats they face,” agrees Pacific Rim Conservation’s Eric VanderWerf, an expert on Hawaiian seabirds. “We need to consider these data in order to make informed decisions about the best conservation measures.”

Declining population trends of Hawaiian Petrel and Newell’s Shearwater on the island of Kaua’i, Hawaii, USA is available at http://americanornithologypubs.org/doi/abs/10.1650/CONDOR-16-223.1.

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.

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Which Extinct Ducks Could Fly?

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Fossils of extinct ducks and geese provide new clues about flightlessness. Photo credit: J. Watanabe

We’re all familiar with flightless birds: ostriches, emus, penguins—and ducks? Ducks and geese, part of a bird family called the anatids, have been especially prone to becoming flightless over the course of evolutionary history. However, it can be difficult to determine from fossils whether an extinct anatid species could fly or not. A new study from The Auk: Ornithological Advances takes a fresh approach, classifying species as flightless or not based on how far their skeletal proportions deviate from the expected anatomy of a flying bird and offering a glimpse into the lives of these extinct waterfowl.

Kyoto University’s Junya Watanabe painstakingly measured 787 individual birds representing 103 modern duck and goose species. From this data, he developed a mathematical model that was able to separate flightless and flying species based on their wing and leg bones—flightless species, the math confirmed, have relatively small wings and relatively large legs. Applying the model to fossil specimens from 16 extinct species identified 5 of the species as flightless, ranging from a land-dwelling duck from New Zealand to a South American duck that propelled itself underwater with its feet.

“I really enjoyed measuring bones in museums and appreciate the hospitality given to me by museum staff. One of the most exciting things was to find interesting fossils that were previously unidentified in museum drawers,” says Watanabe. “What is interesting in fossil flightless anatids is their great diversity; they inhabited remote islands and continental margins, some of them were specialized for underwater diving and others for grazing, and some were rather gigantic while others were diminutive.”

“Dr. Watanabe has developed a valuable statistical tool for evaluating whether a bird was capable of powered flight or not, based on measurements of the lengths of only four different long bones. His method at present applies to waterfowl, but it could be extended to other bird groups like the rails,” according to Helen James, Curator of Birds at the Smithsonian Institution’s National Museum of Natural History. “Other researchers will appreciate that he offers a way to assess limb proportions even in fossil species where the bones of individual birds have become disassociated from each other. Disassociation of skeletons in fossil sites has been a persistent barrier to these types of sophisticated statistical analyses, and Dr. Watanabe has taken an important step towards overcoming that problem.”

Quantitative discrimination of flightlessness in fossil Anatidae from skeletal proportions is available at http://americanornithologypubs.org/doi/full/10.1642/AUK-17-23.1.

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.

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AUTHOR BLOG: Tracking Yosemite’s Spotted Owls

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Tracking Spotted Owls in Yosemite National Park. Photo credit: S. Scherbinski

Stephanie Eyes

Linked paper: California Spotted Owl (Strix occidentalis occidentalis) habitat use patterns in a burned landscape by S.A. Eyes, S.L. Roberts, and M.D. Johnson, The Condor: Ornithological Applications 119:3, August 2017.

In 2005, I happily discovered the Student Conservation Association and that I could be an intern studying California Spotted Owls in Yosemite National Park. I accepted the internship and worked on a PhD student’s project investigating the effects of fire on California Spotted Owl occupancy. The final results from this study revealed that owl occupancy rates were similar between burned and unburned forest, but led to questions about how owls use the mosaic of post-fire patches. In 2010, the former PhD student, my graduate advisor, and I began our efforts to understand this question by capturing owls and affixing radio transmitters to them with the help of several technicians over the course of the three field seasons. By attaching a radio transmitter, we were able to use radio telemetry to triangulate the position of owls during nocturnal foraging bouts. Specifically, we wanted to know how owl foraging patterns are influenced by fire severity, fire-created edges, and other factors such as topography or distance to stream or nest/roost site.

After owls were captured, we set up our telemetry stations along the trails and roads surrounding our known owl roost sites. We went out in teams of two, each armed with a headlamp and an antenna, and worked to locate the owls within our burned sites. Once we initially identified that an owl was present with our antenna, we would split up, one person racing ahead so that we could get three different readings within ten minutes, each separated by about 200 meters, before the owl moved to a new foraging site. While I was relatively experienced with daytime radio telemetry, these nocturnal trail surveys posed a new challenge I enjoyed overcoming, and one time we encountered a curious mountain lion also using the trail searching for (I hoped!) something else.

Whenever we surveyed these trail sites, I remember wondering what the owl was hunting in the burned mosaic of forest patches at the moment that we were trying to pinpoint its location. I’m hoping all my wondering what they were eating will encourage me to go through all the pellets we found in burned forests!

After all the data was collected and analyzed, we learned that owls exhibited habitat selection for locations near roosts and edge habitats, as well as weak selection for lower fire severities. Our results highlight the importance of sustaining forests burned with a mosaic of fire severities with smaller patch sizes of high severity fire. Maintaining this complex mosaic of forest patches and focusing on protecting roost site locations may help sustain California Spotted Owls in the greater landscape.

Spotted Owls Benefit from Forest Fire Mosaic

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California Spotted Owls use a mosaic of fire-created habitat. Photo credit: S. Eyes

Fire is a crucial part of the forest ecosystem on which threatened Spotted Owls rely, but climate change and decades of fire suppression are changing the dynamics of these forests. A new study from The Condor: Ornithological Applications examines California Spotted Owl habitat use in Yosemite National Park and shows that while owls avoid the badly burned areas left behind by massive stand-replacing fires, they benefit from habitat that includes a mosaic of burned patches of different sizes and degrees of severity.

The National Park Service’s Stephanie Eyes (formerly of Humboldt State University) and her colleagues wanted to know how Spotted Owl foraging patterns are influenced by fire severity and fire-created edges, with the goal of informing future fuels reduction efforts and prescribed burning programs. They used radio-transmitters to track movements of 13 owls on eight territories in Yosemite National Park between 2010 and 2012 and found that overall, owls foraged near their roosts and along the edges of patches of burned forest, preferring these edge habitats. Owls selected larger burned patches than the average available size but avoided the interiors of severely burned patches.

“Maintaining a complex mosaic of forest patches with smaller patches of high severity fire can help sustain California Spotted Owls in the greater landscape,” says Eyes. “What’s unique about our study is that we investigated fires that burned within the natural range of variation, so it paints a picture of how owls used a burned landscape before the onset of today’s large stand-replacing fires.” Despite the owls’ preference for edges, there may be a threshold over which edges have a negative effect on habitat quality, and more research is needed to find the right balance between beneficial edge habitat and potentially harmful habitat fragmentation.

“This paper provides new radio telemetry data on how owls use home ranges that have had recent wildfires,” according to the University of Minnesota’s R.J. Gutiérrez, an expert on Spotted Owl habitat use. “Eyes and her colleagues provide a new piece of the puzzle about how owls respond, and they show that this response can be complex. More importantly, because their work occurred within a national park, it will serve as a ‘natural control’ that can be compared with other owl–fire studies occurring on managed forests.”

California Spotted Owl (Strix occidentalis occidentalis) habitat use patterns in a burned landscape is available at http://americanornithologypubs.org/doi/abs/10.1650/CONDOR-16-184.1.

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.

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