DNA Analysis of Bluebird Feces Reveals Benefits for Vineyards

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Western Bluebird feeding its nestlings. Image credit: G. Woods

Do bluebirds nesting in California’s vineyards help grape growers by eating agricultural pests, or hurt them by eating insects that are beneficial? The researchers behind a new study in The Auk: Ornithological Advances found that bluebirds’ presence is likely a net positive—and they did it by analyzing DNA in bird poop.

Bluebirds are one of several groups of birds that catch insects on the wing, but because they’re constantly on the move and the animals they eat are tiny, it’s difficult to determine exactly what species make up their diet. Julie Jedlicka of Missouri Western State University and her colleagues tackled this question using a new approach called “molecular scatology,” analyzing DNA fragments in the birds’ feces to determine insect species the bluebirds were eating. They found that Western Bluebirds in Napa Valley vineyards mostly ate mosquitos and herbivorous insects, likely having only negligible effects on the predaceous insects that benefit vineyard production by eating pests. Jedlicka hopes that these results encourage more vineyard owners to install bluebird boxes, helping replace natural tree cavities lost when land is cleared.

Jedlicka and her colleagues collected 237 fecal samples from adult and nestling bluebirds living on three vineyards in Napa County, California. “Many people I talk to get a very romantic vision in their minds when they think about how beautiful it must be to do fieldwork in California vineyards, especially in the Napa Valley,” says Jedlicka. “Honestly, the landscape was beautiful, but the fieldwork is very demanding. Temperatures during the summer often rose into the 90s and 100s, and I was lucky to have wonderful help from vineyard farm workers and undergraduate field assistants.”

“This study provides important new insights, both in terms of its findings on bluebird diets in vineyard ecosystems and in its advances in molecular diet analyses,” according to Matthew Johnson of Humboldt State University, an expert on ecosystem services provided by birds who was not involved with the study. “Even though the authors did not find specific pest species in bluebird diets, they did confirm that bluebirds are mainly eating herbivorous insects, including those in the same families as major pests. This suggests bluebirds may contribute to ecosystem functioning in these systems. Their work also illustrates the power of new techniques to reveal bird diets and marks new advances in scatology.”

Molecular scatology and high-throughput sequencing reveal predominately herbivorous insects in the diets of adult and nestling Western Bluebirds (Sialia Mexicana) in California vineyards is available at http://americanornithologypubs.org/doi/full/10.1642/AUK-16-103.1.

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.

What Messages Do Female Birds’ Markings Send?

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The dark face masks of female Northern Cardinals vary between individuals. Image credit: J. Jawor

Both male and female birds use traits like plumage brightness to size each other up, but a new study on Northern Cardinals in The Auk: Ornithological Advances shows that the meanings of female birds’ markings may vary from one place to another, even within the same species.

Though they’re often not as showy as the males, female birds have plumage ornaments that can convey information to other members of their species. A previous study found that among Northern Cardinals in Ohio, the brightness of females’ facial markings indicated how aggressive they would be in defending their nests. However, when Caitlin Winters and Jodie Jawor of the University of Southern Mississippi repeated the study in Mississippi’s longleaf pine forest to determine if the same held true there, they were surprised to learn that the variation among females’ facial masks in their southern study population had no relationship to their aggressive behavior.

One of the key differences between the northern and southern cardinal populations studied is that unlike in Ohio, the researchers did not observe any evidence of brood parasitism, where one female cardinal sneaks an egg into another’s nest, among cardinals in Mississippi. The Mississippi birds also had more habitat available to them and defended larger territories, leaving female cardinals there with less need to defend their nests. “This is an indication that selection pressures vary between northern and southern populations and that the information a female in the north needs to convey to other cardinals differs from what a female in the south has to say,” explains Jawor, who has since moved on to New Mexico State University. “The ornament and behavior are both malleable.”

To collect their data, Winters and Jawor captured female cardinals early in the breeding season and measured the brightness of their face masks with a color reflectance spectrometer. They tested aggressive nest defense behavior by waiting until a female left for a break in incubation and then placing a female Northern Cardinal decoy near the nest, observing the bird’s reaction when it returned.

“This is a timely paper, as current research is demonstrating that the factors involved in the display of female aggression are widely varied throughout species,” according to M. Susan DeVries of Edgewood College, who was not involved in the current study. “Considering that different populations are potentially subjected to different selective pressures that can influence behavior, this study’s findings imply that the rules governing aggressive signals and behavior in females are much more complex than we once realized.”

Melanin ornament brightness and aggression at the nest in female Northern Cardinals (Cardinalis cardinalis) is available at http://americanornithologypubs.org/doi/full/10.1642/AUK-16-83.1.

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.

A Hawk’s-Eye View of Raptor Hunting

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Shinta the goshawk wears a head-mounted camera for research. Photo credit: R. Musters

New research from The Auk: Ornithological Advances suggests that the neural processes underlying visual hunting behavior in hawks are similar to those in humans. To study a raptor’s head movements while hunting, the scientists behind the study recruited an unusual research assistant—a Northern Goshawk named Shinta, fitted with a tiny head-mounted camera.

Raptors such as hawks and eagles are visual predators, using their eyesight to navigate their environment and locate and capture prey. To do so, they alternate periods of rapid head or eye movement called saccades with periods where their vision is fixed on a specific point. By studying the mathematical distribution of intervals between saccades, Suzanne Amador Kane of Haverford College, Michael Ochs of The College of New Jersey, and their student collaborators determined that the head movements exhibited by hunting hawks are not regular and predictable; instead, hawks alter the patterns of their head movements based on environmental information, with the time between saccades changing as a bird detects a potential target. This stochastic decision-making strategy is similar to patterns seen in human search behavior.

To gather data, Kane and her colleagues examined archived videos of hunting raptors recorded from the ground, but they also got some hawk’s-eye footage with the help of Shinta the Northern Goshawk, a falconry bird raised in captivity. Wearing a head-mounted camera to record her head movements, Shinta hunted pheasants and rabbits under the supervision of her handler, Robert Musters. “Robert has been a phenomenal falconer to work with on several studies now,” says Kane. “He’s been extremely creative in designing the helmets used to hold the miniature video cameras, as well as expertly flying Shinta during the actual fieldwork.”

“Experienced falconers know that after removing the hood from a bird that is ready to hunt, it will exhibit very characteristic head movements. The really experienced falconer can even read their bird and predict when it is about to take off in pursuit of prey just by watching these head movements,” according to Graham Martin, a University of Birmingham professor and expert in raptor hunting behavior who was not involved with the study. “What cues is the falconer attending to? This work throws some very interesting light on this.”

Sneak peek: Raptors search for prey using stochastic head turns is available at http://americanornithologypubs.org/doi/full/10.1642/AUK-15-230.1. Authors: M.F. Ochs, M. Zamani, G.M.R. Gomes, R.C. de Oliveira Neto, and S.A. Kane.

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.

CT Scans Reveal Birds’ Built-In Air Conditioners

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Image credit: E. Gulson-Castillo, E. Sibbald.

Birds’ beaks come in an incredible range of shapes and sizes, adapted for survival in environments around the world. But as a new study from The Auk: Ornithological Advances reveals, there’s even more to bird beaks than meets the eye—the insides of birds’ bills are filled with complex structures that help them meet the demands of hot climates.

Nasal conchae are complex structures inside bird bills that moderate the temperature of air being inhaled and reclaim water from air being exhaled. Raymond Danner of the University of North Carolina Wilmington and his colleagues from Cornell University and the National Museum of Natural History used CT scans to examine the conchae of two Song Sparrow subspecies, one that lives in warm, dry sand dunes and one that lives in moister habitats farther inland. In this first comparison of conchae structure from birds living along a moisture gradient, the conchae of the dune-dwelling sparrows had a larger surface area and were situated farther out in the bill than those of their inland relatives, hypothetically increasing their beaks’ ability to cool air and recapture water.

Danner and his colleagues used Song Sparrow specimens that were collected in Delaware and the District of Columbia and preserved in ethanol and iodine to help soft tissues show up in scans. The contrast-enhanced CT scans they used to visualize the insides of the sparrows’ bills is a relatively new technique that is letting researchers see the details of these soft, cartilaginous structures for the first time.

“We had been studying the function of the bird bill as a heat radiator, with a focus on heat loss from the external surface and adaptation to local climates, when we began to wonder about the thermoregulatory processes that occur within the bill,” says Danner. “I remember the entire team assembled for the first time, huddled around a computer and looking in amazement at the first scans. The high resolution scans revealed many structures that we as experienced ornithologists had never seen or even imagined, and we were immediately struck by the beauty of the ornately structured anterior conchae and the neatly scrolled middle conchae.”

“This study highlights the remarkable complexity of the rostral conchae in songbirds. This complexity has gone largely unnoticed due to the ways in which most birds are collected and preserved,” according to Jason Bourke, a researcher from the North Carolina Museum of Natural Sciences who was not involved in the research. “Thanks to the use of innovative techniques like diceCT, we are now able to really appreciate just how complicated bird noses can be.”

Habitat-specific divergence of air conditioning structures in bird bills is available at http://americanornithologypubs.org/doi/full/10.1642/AUK-16-107.1. Full author list: Raymond M. Danner, Eric R. Gulson-Castillo, Helen F. James, Sarah A. Dzielski, David C. Frank III, Eric T. Sibbald, and David W. Winkler.

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 form 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.

Tracking Great Reed-Warblers’ Incredible African Migration

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Great Reed-Warblers make an incredible migration between Eurasia and Africa. Photo credit: J. Horns

Populations of many birds that migrate between Eurasia and Africa are in decline, and species that depend on wetlands are especially in trouble. Without knowing what habitats they use throughout their annual wanderings, however, it’s hard to plan effective conservation measures. To fill in these gaps, the researchers behind a new study from The Condor: Ornithological Applications tracked five Great Reed-Warblers over the course of two years, identifying key areas along their amazing cross-continental journeys.

Hoping that Great Reed-Warblers would provide insights that could be applied to other wetland-dependent migrants, Joshua Horns of the University of Utah and his colleagues tagged birds in northeastern Turkey in May 2013. The birds they tracked each visited at least 11 different countries on two continents over the course of their annual migration, passing through the Arabian Peninsula and spending the winter in sub-Saharan Africa. Along the way, their routes took them through as many as 277 Important Bird Areas (IBAs), sites that have been identified as being globally important for bird populations—but more than 40% of the areas the reed-warblers visited receive little or no formal protection. The Aras River wetlands IBA, a rich wetland in eastern Turkey where these birds breed, may be destroyed by a planned dam.

“All of our birds appear to cross the Bab-al-Mandeb strait during spring migration. This means that birds are being funneled into a very small passage, creating a migratory bottleneck,” says Horns. “Especially alarming was the discovery that all the IBAs being used at the Bab-al-Mandeb strait had little to no protection. This is a perfect storm of potential conservation consequences where you have many, many birds relying on a relatively small area and nothing in place to ensure that that area remains suitable.”

Funded by the National Geographic Society, the Whitley Fund for Nature, and the Christensen Fund, Horns and his colleagues tracked the birds via geolocators, tiny devices that record birds’ locations based on sunrise and sunset times. Great Reed-Warblers are great candidates to be tracked via geolocator, because they’re big enough to carry the devices without harm and they return to the same breeding sites each year, allowing scientists to recapture them and retrieve the data recorded. Of the 30 birds they tagged, Horns and his colleagues were able to recapture five.

“Many species of many Afro-Palearctic migrants have declined in the last few decades, and recent tracking studies have begun to unravel the causes,” according York University’s Bridget Stutchbury, a songbird migration expert who was not involved in the reed-warbler research. “This study highlights the enormous challenges of conservation of migratory birds who rely on an intact and healthy network of habitats over thousands of kilometers across the annual cycle.”

Geolocator tracking of Great Reed-Warblers (Acrocephalus arundinaceus) identifies key regions for migratory wetland specialists in the Middle East and sub-Saharan East Africa is available at http://americanornithologypubs.org/doi/full/10.1650/CONDOR-16-63.1.

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.

A Rare Window on the Lives of Young Albatrosses

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Young “prebreeding” birds make up almost half of Oahu’s Laysan Albatross population. Photo credit: E. VanderWerf

Understanding population dynamics is crucial for the conservation of long-lived species like albatrosses, but collecting data on albatrosses before they reach adulthood and begin to breed is challenging. A new study from The Condor: Ornithological Applications provides the first direct estimates of the population size and annual survival of young birds in Oahu’s Laysan Albatross population, giving important new insights into the demographics of these “prebreeders.”

Husband-and-wife team Eric VanderWerf and Lindsay Young of Pacific Rim Conservation spent 14 years banding 477 Oahu albatrosses as chicks and monitoring what became of them. Contrary to the prevailing belief that young albatrosses remain at sea until they’re ready to breed, VanderWerf and Young found that 2% of birds first returned to the colony as one-year-olds, 7% as two-year-olds, and 17% as three-year-olds. These early returners provided a rare window into the lives of young birds, allowing VanderWerf and Young to determine that prebreeders make up almost half of the Oahu population. Once they made it through their first year after fledging, the annual survival of these young birds was very high, estimated at about 97%.

One threat to albatross populations is the mosquito-borne disease known as avian pox virus. “Although albatrosses and many other seabirds have strong immunity to avian pox virus, this disease has a negative long-term effect on their survival and chance of obtaining a mate,” says VanderWerf. “As more albatrosses relocate to higher islands like Oahu in response to sea level rise, where mosquitoes are more prevalent, this disease, and perhaps others, will become a more important threat to the species, so we need to understand more about it and how to prevent its transmission.”

“This study provides novel insight into early life stage demographics of a long-lived seabird from the long-term study of a small and highly tractable colony. It is an excellent example of the value of long-term demographic studies for long-lived species such as albatrosses,” according to Oregon State University’s Robert Suryan, a seabird ecologist who was not involved in the study. “These results are highly relevant to the study, conservation, and management of long-lived species.”

Juvenile survival, recruitment, population size, and effects of avian pox virus in Laysan Albatross (Phoebastria immutabilis) on Oahu, Hawaii, USA is available at http://americanornithologypubs.org/doi/full/10.1650/CONDOR-16-49.1.

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.

What’s Best for Birds in Fire-Prone Landscapes?

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A California Spotted Owl. Photo credit: Rocky Gutiérrez

Two new papers from The Condor: Ornithological Applications demonstrate the complex challenges involved in balancing the management of fire-prone landscapes with the needs of wildlife in the American West.

Salvage logging after a wildfire can provide economic benefits for local communities that depend on the timber industry, but what about birds that rely on recently burned habitat for foraging and nesting? Quresh Latif and Victoria Saab of the U.S. Forest Service and their colleagues assessed how well mathematical models predicting species distributions and guiding management decisions transfer from one location to another. Surveying for Black-backed and Lewis’s woodpecker nests in three locations in Washington, Oregon, and Idaho that had burned within the last five years, they used the data they collected to develop habitat suitability models and then tested model performance at alternate locations. While models that included habitat data collected in the field did better than models that relied only on remote sensing, the models’ overall transferability was limited.

“Broadly applicable predictive models will require integration of field data from multiple wildfire locations,” says Saab. “We hope that managers will apply the habitat suitability models for post-fire forest management planning and decisions in close proximity locations to where the model was developed.”

In California, land managers face a different challenge—how to restore forests overloaded with fuels after decades of fire suppression without causing further harm to the region’s declining Spotted Owl populations. Douglas Tempel and Zachariah Peery of the University of Wisconsin, Rocky Gutiérrez of the University of Minnesota, and their colleagues wanted to know what factors were correlated with changes in occupancy of Spotted Owls throughout the Sierra Nevada ecosystem. Their models show that owls are declining throughout Sierra Nevada except in two national parks protected from typical forest management. Occupancy rates are best explained by the amount of medium and high canopy cover forests within an owl territory. Based on this finding and others, they suggest that judicious use of forest fuels treatments that reduce canopy cover could be used in some areas without driving the owls away.

“We’re not suggesting that they do this within the core parts of the territory that the owls use for nesting and roosting,” says Gutiérrez. But in the long term, returning the region to a more natural fire regime might actually benefit the owls by reducing the likelihood of intense, large-scale fires that can damage the old-growth habitat on which Spotted Owls rely.

“We were unable to distinguish stands characterized by medium and large trees,” adds Peery. “As a result, a key uncertainty involves the extent to which changes in the prevalence of large trees in territories impacts Spotted Owl occupancy and demographics, an issue that requires additional study.”

In both California and the Northwest, meeting the short-term habitat needs of birds while promoting the long-term health of forests and local communities is a delicate balancing act. However, the dedicated scientists and land managers behind these two studies suggest that if habitat and population data is carefully applied when creating management plans, it may be an achievable goal.

Transferability of habitat suitability models for nesting woodpeckers associated with wildfire is available at http://americanornithologypubs.org/doi/abs/10.1650/CONDOR-16-86.1Meta-analysis of California Spotted Owl (Strix occidentalis occidentalis) territory occupancy in the Sierra Nevada: Habitat associations and their implications for forest management is available at http://americanornithologypubs.org/doi/full/10.1650/CONDOR-16-66.1.

About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology published by the American Ornithological Society. It began in 1899 as the journal of the Cooper Ornithological Club, a group of ornithologists in California that became the Cooper Ornithological Society.