Where Do Crows Go in Winter?

AUK-18-23 M Jones

A crow with a satellite transmitter. Photo credit: M. Jones

“Partial migration”—where some individuals within a population migrate and some don’t—is common among birds and is speculated to be a step on the evolutionary path to complete, long-distance migration, but scientists know very little about how it actually works. A new study from The Auk: Ornithological Advances tracks where American Crows go during the winter and shows that while individuals are consistent in whether they migrate or stay put, partial migration might give them enough flexibility to adapt to changing environmental conditions.

Hamilton College’s Andrea Townsend and her colleagues captured crows in large winter flocks in Utica, New York, and Davis, California, fitting them with satellite transmitters to track their movements and collecting blood and feather samples. Their data show that 73% of western crows and 86% of eastern crows migrated at least some distance to breed, with an average journey of around 500 kilometers. Birds returned faithfully to the same breeding territory each year, and whether or not individuals migrated was consistent from one year to the next—they didn’t switch strategies depending on environmental conditions. However, they were flexible in where they spent the winter.

This information can serve as an important baseline for tracking how crows’ migratory behavior is affected by factors including climate change and urbanization. Urban “heat islands,” as well as general warming trends, could lead more birds to shorten their migration and spend the winter closer to their breeding territory. “If you live in a place, usually a city, with a huge winter flock of crows, you are seeing migratory birds that came south for the winter as well as your local, year-round crows,” says Townsend. “Personally, I find the sight of an 8000-crow roost exhilarating, but if they or their feces are driving you crazy, you can at least take comfort in knowing that most of them will disappear in early March.”

“It is surprising how much remains unknown about the seasonal movements of most partial migrant species, and this is especially true for variability among populations,” adds the Smithsonian Migratory Bird Center’s Emily Cohen, an expert on migration patterns who was not involved with the study. “This kind of information about populations-specific annual movements is not trivial to collect, but is fundamental to understanding most aspects of the evolution and ecology of species.”

Where do winter crows go? Characterizing partial migration of American Crows with satellite telemetry, stable isotopes, and molecular markers is available at http://www.bioone.org/doi/full/10.1642/AUK-18-23.1.

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology published by the American Ornithological Society. The Auk commenced publication in 1884 and in 2009 was honored as one of the 100 most influential journals of biology and medicine over the past 100 years. The Auk has the #1 average Journal Impact Factor for the past 5 years for ornithology journals.

AUTHOR BLOG: Ancient Fossil Bones of a Recently Extinct Cormorant

Junya Watanabe

Linked paper: Pleistocene fossils from Japan show that the recently extinct Spectacled Cormorant (Phalacrocorax perspicillatus) was a relict by J. Watanabe, H. Matsuoka, and Y. Hasegawa, The Auk: Ornithological Advances 135:4, October 2018.

The new and heretofore unfigured species of the birds of North America

Live reconstruction of the Spectacled Cormorant from study skins. Artwork by Joseph Wolf, from Elliott (1869), The New and Heretofore Unfigured Species of the Birds of North America, Volume 2.

Numerous extinction events have taken place in geologically recent time, caused to varying degrees by human activity. Although relatively much is known about how humans have given “final blows” to animal species in recent history, little is known about the long-term biogeographic and evolutionary history of extinct animals. This is where archaeological and fossil records play crucial roles. One of the most (in)famous examples of historic extinctions is the case of the Great Auk, which was once widespread in the North Atlantic Ocean but was driven to extinction in the mid-19th century due to hunting by humans. There is one potential parallel, though less widely known, in the North Pacific Ocean; a large seabird species called Spectacled Cormorant (Phalacrocorax perspicillatus) was driven to extinction almost contemporaneously. This species was first discovered in the 18th century on Bering Island, part of the Commander Islands, by German explorer Georg Steller, who became the only naturalist to observe the birds in life. Following the colonization of the island by humans in the early 19th century, this species was hunted by humans, and it was driven to extinction in the 1850s. As there has been no record of the species outside Bering Island, it is considered to have been restricted to the island throughout its existence. Our new study in The Auk: Ornithological Advances, however, reports the first definitive record of the cormorant species outside Bering Island, demonstrating that the species was in fact not restricted to the island in the past.

Through our study of Japanese fossil birds, my colleagues and I identified 13 fossil bones of the Spectacled Cormorant from upper Pleistocene deposits (dated ~120,000 years ago) in Japan. The fossil bones were recovered from Shiriya, northeastern Japan, through excavations led by my co-author Yoshikazu Hasegawa of the Gunma Museum of Natural History. Through detailed examination of the bird fossils from the site, it became evident that a cormorant species much larger than any of the four native cormorant species in present-day Japan was represented in the material. At first, we suspected the presence of a new species, but this turned out not to be the case. Through a literature survey, I came across a 19th-century paper by American ornithologists Leonhard Stejneger and Frederic Lucas that described bones of the Spectacled Cormorant collected on Bering Island. The dimensions and illustrations given in the paper were strikingly similar to the Japanese fossils. I decided to visit the Smithsonian Institution’s National Museum of Natural History in Washington, D.C., where the bones described by Stejneger and Lucas are stored. After careful examination, the Japanese fossils turned out to agree in every detail with bones of the Spectacled Cormorant from Bering Island, rather than with any other species compared, to the extent that I was convinced that the Japanese fossils belong to the same species as the Bering Island bones.

The occurrence of the Spectacled Cormorant from Japan is the first definitive record of this species outside Bering Island and indicates that the species underwent a drastic range contraction or shift since the Pleistocene. In other words, the population of this species on Bering Island discovered by Steller was in fact a relict, with most of the species’ past distribution already lost. Changes in oceanographic conditions might be responsible for the local disappearance of the species in Japan; paleoclimate studies have shown that the oceanic productivity around Shiriya dropped drastically in the Last Glacial Maximum (~20,000 years ago), which would have seriously affected the population of the species. Although it might be possible that hunting of that species by humans took place in prehistoric Japan, no archaeological evidence for that is known so far. The entire picture of the recent extinction event of the Spectacled Cormorant might be more complex than previously thought, as is becoming evident for some other extinct seabirds in other parts of the world.

Further reading

Fuller, E. (2001). Extinct Birds, revised edition. Cornell University Press, New York, NY.

Hume, J. P. (2017). Extinct Birds, 2nd edn. Bloomsbury Natural History, London.

Rainy weather predicts bird distribution—but climate change could disrupt it

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Precipitation is the best predictor of Eastern Kingbirds’ winter distribution. Image credit: M. MacPherson

Understanding what environmental cues birds use to time their annual migrations and decide where to settle is crucial for predicting how they’ll be affected by a shifting climate. A new study from The Auk: Ornithological Advances shows that for two species of flycatcher, one of the key factors is rain—the more precipitation an area receives, the more likely the birds are to be there during the non-breeding season.

Tulane University’s Maggie MacPherson and her colleagues combined field techniques with species distribution models to investigate which environmental factors drove the migrations of Eastern Kingbirds and Fork-tailed Flycatchers. Using geolocators, devices that record a bird’s daily location based on day length, they could track where individuals of each species went. The two species share similar behavior and habitat requirements, but differ in their range and migration strategies, and these strategies were compared to determine the influence of temperature, precipitation, and primary productivity (the amount of “green” vegetation). Precipitation turned out to be one of the most important predictors of their distribution, particularly in the non-breeding season.

MacPherson comments, “Although we understand how climate change is expected to affect regional temperature regimes, changes in patterns of seasonal precipitation remains unclear. As the locations of both species were positively correlated with the highest rainfall across the landscape during their non-breeding seasons, our research emphasizes the need for a better understanding of how flexible they may be in adjusting locations under new rainfall regimes. More research is needed to better understand how migratory birds relying on current rainfall regimes could benefit from climate-conscious conservation planning.”

“In the face of climate change, having seasonal species distribution models like these is powerful for helping understand the biology of the species, and also for predicting how a population might change in size and geography in the future, or a species’ flexibility to adjust its migratory timing,” adds Mississippi State University’s Auriel Fournier, an expert on species distribution models who was not involved in the study. “All of those predictions are vital for conservation planning and decision making. The use of two related species with different life history traits is also exciting, as it makes the results more broadly applicable.”

Follow the rain? Environmental drivers of Tyrannus flycatcher migration across the New World is available at http://www.bioone.org/doi/full/10.1642/AUK-17-209.1.

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology published by the American Ornithological Society. The Auk commenced publication in 1884, and in 2009 was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

Crows are always the bullies when it comes to fighting with ravens

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Three Crows (left) versus one Raven (right) (Photo credit: PhillipKrzeminski)

A study from The Auk: Ornithological Advances presents citizen science data which supports that American Crows and Northwestern Crows almost exclusively (97% of the time) instigate any aggressive interactions with Common Ravens no matter where in North America. The data showed that aggression by crows was most frequent during the breeding season, most likely due to nest predation by ravens. This study not only gives insight into interspecies dynamics, but also how citizen science data can aid behavioral studies at large geographic scales.

Cornell University’s Ben Freeman and colleagues used more than 2,000 publicly collected and submitted observations from across North America via eBird to analyze the interspecific aggression between crows (American and Northwestern) and Common Ravens. From these records, it was determined that crows were the predominant aggressor. Crows primarily attacked in small groups rather than one-on-one confrontations with ravens. The breeding season was when most of the attack observations were made, suggesting that nest predation by ravens influences this behavior. Aggression during the winter is potentially explained by crows preemptively deterring nest predation and defending resources needed for nesting later in the year. This study was made possible by citizen scientists who were not even asked to submit such observations. Given this was passively collected data that aided in a behavioral study on a large geographic area, it could act as a model for other research and potential studies conducted.

Lead author Ben Freeman comments, “There are two take-home messages. First, we show that bigger birds do not always dominate smaller birds in aggressive interactions, and that social behavior may allow smaller birds to chase off larger birds. Second, this is a case example of the power of citizen science. It would be next to impossible for even the most dedicated researcher to gather this data across North America. But because there are thousands of people with expertise in bird identification and an interest in bird behavior, we can use data from eBird to study behavioral interactions on a continental scale.”

“Given that aggression between crows and ravens can be quite conspicuous, birders and the general public are often the observers of such interactions,” adds Kaeli Swift of the University of Washington, who was not involved with the research, “yet despite the ease and frequency of witnessing these events, there was little scientific information for curious minds to turn to for explanation. It’s quite rewarding then, that the citizen scientists that may have wished for this information are the very people whose observations made this publication possible.

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Why do crows attack ravens? The role of predation threat, resource competition and social behavior is available at http://www.bioone.org/doi/full/10.1650/AUK-18-36.1.

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology published by the American Ornithological Society. The Auk commenced publication in 1884, and in 2009 was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

To help save Northern Spotted Owls, we need to prevent kissing cousins

Auk-18-1_Spotted Owl_Alan Dyck

Spotted Owl (Photo Credit: Alan Dyck)

The Auk: Ornithological Advances presents a study on a Northern Spotted Owl pedigree, consisting of almost 14,200 individuals over 30 years, which determined inbreeding varies across the species’ range. Selection against inbreeding based on decreased future reproduction, fewer offspring, and overall survival of individuals was also supported. These results indicate that Spotted Owl conservation efforts need to address owl breeding more. Another implication of this work is the need to increase genetic diversity to prevent further population decline.

Mark Miller of the United States Geological Survey (USGS) Forest and Rangeland Ecosystem Science Center, and colleagues employed field and statistical methods to create a family tree for Northern Spotted Owls living in California, Oregon, and Washington. From this, the researchers determined how often inbreeding occurs in the wild for these birds. Fourteen types of matings among relatives were determined with most inbreeding relationships being between half or full siblings. It was discovered that inbreeding is most common in the Washington Cascades (~15% of individuals are inbred), while the lowest inbred population was Northern California (~2.7% of individuals). The explanation for this geographic variation may be the rate at which specific populations are declining and experiencing bottlenecks. Conservation efforts are vital today given that Northern Spotted Owls are already facing habitat loss and competition with a similar species, the Barred Owl. This study showed that both the physical consequences of inbreeding (physical deformities, reduced ability to adapt) and the reproductive fitness of individual birds (infertility, future reproduction, decreased survival) need to be taken into account since both influence this species’ success. Translocating birds among populations to help increase the genetic diversity may be a potential management strategy.

Lead author Mark Miller comments, “Long-term studies, similar to the one described in this paper, are key to understanding how common or rare inbreeding is in natural populations. An understanding of the extent of inbreeding can help resource managers better identify appropriate measures to conserve threatened and endangered species.”

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Variation in inbreeding rates across the range of Northern Spotted Owls (Strix occidentalis caurina): Insights from over 30 years of monitoring data is available at http://www.bioone.org/doi/full/10.1650/AUK-18-1.1.

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology published by the American Ornithological Society. The Auk commenced publication in 1884, and in 2009 was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

Nominees for BioOne Ambassador Award

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

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

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

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

Terns Face Challenges When They Fly South for Winter

AUK-17-210 C Henderson

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

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

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

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

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

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

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