What really did come first—the chicken or the egg? Birds’ reproductive biology is dramatically different from that of any other living vertebrates, and ornithologists and paleontologists have long wondered how and when the unique features of bird reproduction originated. A new Review in The Auk: Ornithological Advances examines answers from three sources—modern birds, fossils of primitive birds, and fossils of the dinosaurs from which birds are descended—to shed new light on the subject.

All modern birds share certain reproductive features, such as a single functional ovary and the practice of incubating their eggs through direct contact. Analysis of the bird family tree also suggests that early birds built simple, open nests on the ground and that their young were “precocial,” meaning they were well-developed and almost ready to fend for themselves when they hatched. Those dinosaurs close to the ancestry of birds shared some of these traits, but they had two functional reproductive tracts, and their eggs were smaller relative to their body size and more elongated than those of modern birds.

Fossils of primitive birds and eggs from the Mesozoic era place them midway between their dinosaur ancestors and their modern descendants, with eggs between those of pre-avian dinosaurs and modern birds in term of size and shape. In this way, David Varricchio and Frankie Jackson of the Montana State University are able to trace the evolution of bird reproduction through a series of distinct stages, from pre-avian dinosaurs to the birds of today.

“Reproduction in modern birds is distinct among living vertebrates. Many aspects of this reproduction mode trace their origin to theropod dinosaurs such as Oviraptors and Troodontids, but not really beyond them to more distantly related dinosaurs,” according to Varricchio. “Interestingly, reproduction in the most common group of Mesozoic birds is very similar to that of these dinosaurs, and so still differs from modern birds. Consequently, modern birds stand apart from Mesozoic birds, and perhaps this contributed to their surviving the end-Cretaceous extinction event.”

Reproduction in Mesozoic birds and evolution of the modern avian reproductive mode is available

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. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

Shorebirds breeding in Alaska are being exposed to mercury at levels that could put their populations at risk, according to new research from The Condor: Ornithological Applications.

Thanks to atmospheric circulation and other factors, the mercury that we deposit into the environment tends to accumulate in the Arctic. Mercury exposure can reduce birds’ reproductive success and sometimes even be lethal. Shorebirds may be particularly vulnerable because they forage in aquatic environments where mercury is converted into methylmercury, its most dangerous form. Marie Perkins of the Biodiversity Research Institute (BRI) and her colleagues investigated the level of mercury in Alaska’s shorebirds and found that some birds breeding near Barrow, at the state’s northern end, have mercury concentrations upwards of two micrograms per gram of blood.

“These species already face a lot of tough new challenges, from climate change to disappearing stop-over habitat, so throwing a neurotoxin in the mix that can reduce reproductive success is likely to harm their populations,” according to Dan Cristol of the College of William & Mary, an expert on mercury in birds who was not involved with the new study. “The mercury concentrations reported in this paper are likely to reduce reproduction, but not catastrophically, based on what we know from other species. What may be even worse, though, is that these mercury levels probably spike when they leave the breeding grounds and start burning their reserve fuel, making their already arduous continent-jumping trips even harder.”

To assess the birds’ mercury exposure, Perkins and her colleagues collected blood and feathers from nine shorebird species breeding and staging for their southward migration at sites throughout Alaska. In addition to the troubling results from birds breeding near Barrow, they found that mercury levels depended on a species’ foraging habits—shorebird species that foraged in upland areas, away from methylmercury-rich wetlands, had the lowest blood mercury concentrations.

More work is needed to determine how much mercury various shorebird species can handle before they suffer adverse effects. “These results have encouraged me to expand my research on mercury exposure in Arctic shorebirds,” says Perkins. “I am currently pursuing my PhD at McGill University, where I am working in collaboration with BRI and the Arctic Shorebird Demographics Network to closely examine mercury exposure in multiple shorebird species breeding across the North American Arctic.”

Mercury exposure and risk in breeding and staging Alaskan shorebirds is available at http://www.aoucospubs.org/doi/full/10.1650/CONDOR-16-36.1.

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.

This week marks the end of our series of blog post highlighting both our journals’ top cited articles from 2014 and 2015. After counting down from number ten, today we reveal that The Condor‘s most cited paper from this time period was…

Bird–building collisions in the United States: Estimates of annual mortality and species vulnerability by S.R. Loss, T. Will, S.S. Loss, and P.P. Marra, from the February 2014 issue of The Condor: Ornithological Advances.

Loss and his colleagues reviewed the published literature and acquired unpublished datasets to systematically estimate annual bird mortality from window collisions in the U.S. and identify particularly vulnerable species. They found that 365–988 million birds are killed in such collisions each year, supporting the conclusion that building collision mortality is one of the top sources of human-caused bird mortality in the U.S. A large proportion of all mortality occurs at structures like houses that kill small numbers of birds on a per-building basis but make up a high percentage of all buildings, which suggests that achieving a large overall reduction in mortality will require mitigation measures to be applied across a large number of structures (not just high-rises).

For some species, including Golden-winged Warblers, Painted Buntings, Kentucky Warblers, and Canada Warblers, building collision mortality appears substantial enough to contribute to or exacerbate ongoing population declines. The authors suggest that a feasible long-term approach to reducing mortality would be the continued adaptation of Green Building certification standards to include bird collision risks.

Two of North America’s declining grassland songbirds may be particularly vulnerable to altered weather patterns caused by climate change, according to new research in The Condor: Ornithological Applications.

Extreme heat waves have been known to kill adult birds, and droughts can cause birds to abandon nests or skip breeding altogether. To learn what species might be at greatest risk, Jessica Gorzo of the University of Wisconsin-Madison and her colleagues analyzed more than four decades of bird survey data from the Dakotas, Montana, and Wyoming, looking for patterns linking grassland bird abundance to temperature and precipitation.

Of the 14 bird species the researchers focused on, 5 showed significant associations with weather trends, their populations appearing to increase or decrease depending on whether a year had been particularly warm, cold, wet, or dry. Two, the closely related Grasshopper and Baird’s sparrows, are already declining enough to concern conservationists, and this study shows that they may be particularly vulnerable to the warmer, drier conditions that are likely becoming more frequent due to climate change.

“With climate change, there are bound to be winners and losers,” according to Gorzo. “Of the species we considered, Grasshopper and Baird’s Sparrows may be imminently at risk. These species responded similarly to our weather metrics, which made sense in light of their shared life history traits. Knowing that these species need tall, lush grassland vegetation, increasingly dry conditions could inhibit the growth they need to be successful.”

The data for the study came from the North American Breeding Bird Survey, a program for which skilled volunteer birders conduct annual bird counts along set routes. “It was really an honor to work with this dataset, because though I don’t run a route myself, I have many friends who have been visiting the same route year after year and take pride in what they contribute to our understanding of the continent’s birds,” says Gorzo. “It is a tremendous volunteer effort that takes skill, dedication and hard work. To be able to put it to good use to elucidate some patterns relevant to climate change felt really rewarding, and I can’t thank birders over the decades enough for working year in and year out to add to this dataset.”

Using the North American Breeding Bird Survey to assess broad-scale response of the continent’s most imperiled avian community, grassland birds, to weather variability is available at http://www.aoucospubs.org/doi/full/10.1650/CONDOR-15-180.1.

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.

Many birds learn their songs from their parents, but what if they could get a head start? A new paper in The Auk: Ornithological Advances demonstrates that some songbirds start learning to imitate their parents before they even hatch.

Vocal learning has many benefits for birds—it lets them signal their suitability as a potential mate, recognize their relatives, and enhance their social interactions. Once Diane Colombelli-Négrel and Sonia Kleindorfer of Australia’s Flinders University, Mark Hauber of New York City’s Hunter College, and their colleagues from Cornell University discovered that Superb Fairywren nestlings learn to imitate their mothers’ calls while still in the egg, they wanted to see whether the behavior extended to other species and to learn more about its ecological context, so they turned to the related Red-backed Fairywren.

All Red-backed Fairywren females in this new study called to their eggs while incubating, and most continued to call to their nestlings for five to six days after they hatched. As a result, mother and offspring calls were more similar than would be expected by chance. Parents also put more effort into feedings nestlings with calls similar to their own. “Fairywrens have become a new model system in which to test new dimensions in the ontogeny of parent-offspring communication in vertebrates,” says Hauber.

Though the researchers had hypothesized that fairywren parents could use calls to identify alien nestlings, the result of eggs placed in their nests by parasitic cuckoos, the rate at which Red-backed Fairywren mothers called to their eggs did not increase significantly when more cuckoos were present in the habitat. Colombelli-Négrel and her colleagues speculate that the similarity of nestlings’ calls to their own could also tip parents off about which nestlings are the most vigorous and the best learners, so that they can invest more resources in the ones most likely to thrive.

The original discovery was a fortuitous accident. “Because fairywrens have high predation rates, we originally placed microphones under Superb Fairywren nests to record alarm calls against predators twenty-four seven,” says Colombelli-Négrel. “As a result, we discovered embryonic learning in Superb Fairywrens.” When they turned to Red-backed Fairywrens, they recorded vocalizations from 67 nests across four breeding seasons in Queensland, as well as playing recordings of begging nestlings to test parents’ responses.

“Prenatal vocal learning has rarely been described in any animal, with the exception of humans and Australian Superb Fairywrens,” says Dr. William Feeney of the University of Queensland, an expert on the interactions between cuckoos and host birds. “In this study, the authors present data suggesting that, like the Superb Fairywren, Red-backed Fairywrens also learn their begging calls from their mother. This result is exciting as it opens the door to investigating the taxonomic diversity of this ability, which could provide insights into why it evolves.”

Vocal imitation of mother’s calls by begging Red-backed Fairywren nestlings increases parental provisioning is available at http://www.aoucospubs.org/doi/full/10.1642/AUK-15-162.1.

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. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

Tiny Ruby-throated Hummingbirds are capable of flying more than 2,000 kilometers without a break, according to a new paper in The Auk: Ornithological Advances. This research provides some of the first details of their annual fall journey from the eastern United States to Central America, showing that their fall migration peaks in September and that older birds travel ahead of younger ones.

Collecting data on birds passing through southern Alabama, Theodore Zenzal of the University of Southern Mississippi and his colleagues found that hummingbirds moved through the area between late August and late October, with older birds arriving earlier and in better condition. Using a computer program to estimate flight range based on birds’ mass and wingspan, they estimated that the average hummingbird has a flight range of around 2,200 kilometers. Older birds and males were predicted to be able to travel farther at a time than younger birds and females.

These results suggest that older birds are more experienced and socially dominant, leaving their breeding territories earlier and traveling faster. Whether Ruby-throated Hummingbirds migrate across the Gulf of Mexico or around it is still unknown, but the flight ranges researchers calculated mean that most of them would be able to make it across if weather conditions were favorable. “The most interesting thing, in my opinion, is how some of these birds effectively double their body mass during migration and are still able to perform migratory flights, especially given some of the heftier birds seem to barely make it to a nearby branch after being released,” says Zenzal, whose work was funded in part by the National Geographic Society.

Zenzal and his colleagues captured hummingbirds with mist nets at Alabama’s Bon Secour National Wildlife Refuge during the fall migrations of 2010–14, banding and recording data on an amazing 2,729 individual hummingbirds. Even a visiting documentary crew was charmed by the tiny birds. “All but one person on the crew was from Europe and most had never seen a hummingbird in real life, so you can imagine how fascinating these birds must have seemed,” says Zenzal. “During the course of filming, members of the crew would regularly ask me to place a hummingbird in their hand so they could release it.”

“Patterns we previously had hints of from small, anecdotal observations are documented here with a very large sample size. It’s interesting that the young of the year migrate after adults and are quite different in their stopover phenology. This suggests there are substantial differences between flying south for the first time, as opposed to flying somewhere again as an adult,” says UC Riverside’s Chris Clark, an expert on hummingbird behavior. “I think that further research on how young hummingbirds migrate, and the decisions they make, would be really interesting.”

Stopover biology of Ruby-throated Hummingbirds (Archilochus colubris) during autumn migration is available at http://www.aoucospubs.org/doi/full/10.1642/AUK-15-160.1.

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. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

Songbird nestlings in the Arctic struggle in cold, wet years, but the changes forecast by climate models may lead to even more challenging conditions, according to new research in The Auk: Ornithological Advances.

Jonathan Pérez of the University of California, Davis, and his colleagues compared the growth rates of the nestlings of White-crowned Sparrows, which have a broad breeding range, with those of Lapland Longspurs, which are an Arctic breeding specialist. They predicted that nestlings would grow faster in warmer, drier conditions, that clutches laid earlier would do better, and that the nestlings of specialist longspurs would grow faster than the generalist sparrows.

They found that growth rates were higher overall in 2013 than in 2014, when the weather was colder and wetter. There were also fewer arthropods, the birds’ food source, available in 2014. Longspur nestlings grew faster than sparrow nestlings both years, but sparrows were unaffected by temperature, perhaps because sparrows nest in shrubs rather than on the open tundra. Nestlings from clutches that were laid earlier did grow faster than those from later clutches, since birds that arrived on their breeding grounds early could claim the best territories for raising young.

Challenging conditions force parents to make a choice between taking care of themselves and taking care of their offspring. Climate change is likely to bring new uncertainty for birds nesting in the Arctic—while warmer temperatures will favor higher nestling growth rates, climate models also predict more frequent storms and increased precipitation.

The research was carried out on the North Slope of Alaska’s Brooks Range, where researchers tracked 110 White-crowned Sparrow nestlings and 136 Lapland Longspur nestlings over two years, representing 58 total nests. Perez had previously studied parental energy expenditure and incubation. “When I became involved in our project based out of Toolik Lake looking at effects of interannual variation across trophic levels and how that ultimately plays out in terms of reproductive success of songbirds, expanding to an examination of nestling growth rates with regards to variation in environmental conditions seemed like a logical next step,” he says.

“Species at range edges are sentinels of climate change because they often experience high environmental variability and harshness,” according to Dr. Daniel Ardia of Franklin and Marshall College, an expert on the role of environmental variation in bird behavior and physiology. “Pérez and his co-authors reveal the direct effects of weather variation on nestling growth, an important determinant of fitness, showing how climate variability might have strong negative effects of populations. What makes the study so compelling is that they were able to link weather variability to food supply showing the causal link between predicted weather variation and reproduction.”

Nestling growth rates in relation to food abundance and weather in the Arctic is available at http://www.aoucospubs.org/doi/full/10.1642/AUK-15-111.1.

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. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

A new Review in The Condor: Ornithological Applications explores how oaks and pines depend on corvids, the group of birds that includes ravens, crows, and jays, to reproduce and spread—and how birds may be the key to helping these valuable trees weather the challenges of habitat fragmentation and climate change.

Corvids store seeds in small caches spread across the landscape, a behavior called “scatter-hoarding.” Birds cache more seeds than they eventually eat, so some seeds sprout and scatter-hoarding becomes seed dispersal, helping trees colonize new areas. Many oaks and pines have specific adaptations to encourage dispersal by birds, producing large, nutritious seeds with protective chemicals that keep them from rotting, which encourages scatter-hoarding by eliminating the need for animals to eat the seeds immediately.

The Review by Mario Pesendorfer of the University of Nebraska–Lincoln and his colleagues at the Smithsonian Migratory Bird Center, Cornell Lab of Ornithology, and The Nature Conservancy explores specific examples of such relationships from around the world. In Europe, Eurasian Jays are proving to be a crucial ally for oaks as habitat fragmentation and climate change increasingly impact European hardwoods. In the western U.S., researchers have shown that repeated long-distance dispersal events by Clark’s Nutcrackers are essential to establish and maintain Ponderosa Pine populations and that Pinyon Jays help maintain the tree’s genetic diversity. And in the eastern U.S., Blue Jays speed forest fire recovery by increasing their caching effort after fires and selecting canopy gaps as cache sites.

Harnessing this bird behavior may aid habitat restoration. Europeans have been aware of the relationship between jays and oaks for centuries, and managers in some areas of Western Europe are planting small stands of seed-source trees and relying on corvids to help disperse them across the landscape. In America, conservationists are exploring the possibility of reintroducing Channel Island Scrub-Jays to islands where they were extirpated to speed the recovery of oak and pine vegetation after livestock removal.

“In light of the globally changing climate and increasing habitat fragmentation, these winged dispersers that transport seeds over long distances are likely to become more important, as they enable plant populations to shift their range,” says Pesendorfer. “Since oaks and pines are important keystone species that themselves provide habitat for hundreds of animal species, such dispersal can have ecosystem-wide benefits.”

Scatter-hoarding corvids as seed dispersers for oaks and pines: A review of a widely distributed mutualism and its utility to habitat restoration is available

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.

Wading birds in many parts of the world use agricultural habitats such as flooded rice fields, but in the southeastern U.S., Great Egrets (Ardea alba) prefer natural wetlands over any other habitat type, according to a new study in The Condor: Ornithological Applications. Researchers tracking habitat use by Great Egrets in Louisiana and South Carolina found that while some human-influenced wetlands, such as ponds and crayfish production impoundments, did attract egrets, this preference varied between regions. Overall, Great Egrets preferred to forage in natural wetlands.

Human-influenced wetlands such as fish hatcheries, flooded agricultural fields, and artificial ponds and reservoirs represent a rising percentage of the world’s wetland areas, and in some areas these may offer enhanced foraging opportunities for wading birds. Jason Fidorra, formerly of the University of Florida and now with the Washington Department of Fish and Wildlife, and his colleagues captured Great Egrets in southern Louisiana and coastal South Carolina and fitted them with backpack transmitters to learn how these birds used available wetland habitats. They also conducted aerial surveys of a breeding population in Louisiana, where nesting colonies located on a boundary between agricultural and natural wetlands provided an ideal opportunity to observe the birds’ habitat preferences.

In both South Carolina and Louisiana, satellite tracking revealed that the most commonly used foraging habitat was natural wetlands; human-influenced ponds and lakes were the second most popular habitat type in South Carolina, while rivers were second-most popular in Louisiana. Satellite-tagged birds did not use flooded agricultural fields at all during the study. In aerial surveys, the only human-influenced habitat the egrets preferred to natural wetlands was impoundments for crayfish production, not rice fields.

Catching egrets required a bit of ingenuity. “We spent several months learning ways not to catch an egret, and the successful method was something I don’t claim credit for,” says Fidorra about the pneumatic net guns used in the study. “It was a colleague, Danny Caudill, who suggested it. Of course, since we were often working within urban areas we couldn’t use the actual guns that are normally modified to shoot nets. Instead, Caudill came up with some DIY instructions for an air-powered net gun that he pieced together at a hardware store for about $35. In the end it turned out to be a versatile and effective tool—and a lot of fun, of course.”

Their results show that despite the importance of agricultural fields for wading birds in some parts of the world, natural wetland habitat is usually preferred by Great Egrets in the U.S. “Rice fields have been fairly well studied as bird habitat in many parts of the world, but much less so in Louisiana,” says Fidorra. “We found that while Great Egrets did use rice fields, they were never selected more strongly than natural wetlands. This suggests that they are less-than-adequate replacements to natural wetlands.”

“Long-legged wading birds have long been emblematic of freshwater and estuarine wetlands, ponds, lakes and rivers. Their health and abundance is an expression of the productivity of those habitats that have been so altered by humans for agriculture and suburban development over the past century,” adds John Brzorad of Lenoir-Rhyne University, an expert on egret movements and energy requirements. “This study is an excellent reaffirmation of the conservation value of natural wetlands and will further stimulate research on the value of golf course, suburban and retention ponds using advancing telemetry methods.”

Selection of human-influenced and natural wetlands by Great Egrets at multiple scales in the southeastern USA 

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.

Gulls have learned to follow diving ducks and take the bottom-dwelling mussels that the ducks bring to the surface, a food source that would otherwise be inaccessible to them. Gulls are one of the most adaptable groups of birds, able to exploit a wide variety of food resources and respond to new opportunities, and a study forthcoming in The Auk: Ornithological Advances documents this previously unrecognized behavior in Herring Gulls (Larus argentatus) and Mew Gulls (Larus canus) on a brackish lagoon on the Germany–Poland border.

Ducks wintering on Szczecin Lagoon dive to the bottom to forage on zebra mussels, bringing clumps of mussels to the surface and regularly losing fragments in the process. To determine whether the gulls on the lagoon take advantage of this or if their presence while the ducks are foraging is only a coincidence, Dominik Marchowski of Szczecin University and his colleagues observed the behavior of the birds between October 2013 and November 2014, watching three species of duck—the Common Pochard (Aythya ferina), Tufted Duck (A. fuligula), and Greater Scaup (A. marila)—through spotting scopes. They recorded how intensely the ducks were foraging and whether any gulls were present, and they also collected gull pellets to confirm what they were eating.

The more ducks in a flock were foraging, the more likely gulls were to be present. Gulls’ behavior toward the ducks fell into two categories: They picked up mussel fragments that the ducks lost, a form of one-way symbiosis called commensalism, but also stole fragments from the ducks directly, which is called kleptoparasitism. Both methods allowed the gulls to gain access to food that, being poor divers themselves, they wouldn’t have been able to reach otherwise. Pellet analysis confirmed that the diet of the gulls at the lagoon changes dramatically when the ducks show up for the winter, shifting from mostly fish to mostly mussels.

“Gulls were initially on the margins of our research. Initially, their interaction with the ducks seemed obvious, but after analyzing the available literature, it turned out that little is known about it,” says Marchowski. “The marginal study became major, and we developed behavioral studies of birds and an analysis of pellets to confirm the scale of the phenomenon. In our opinion, these studies show that it’s worth watching the seemingly obvious behavior of birds more closely, because they can hide interesting interactions.”

“This investigation provides rare and convincing evidence that demonstrates how interspecific feeding interactions between Larus gulls and diving ducks influence community structure in the vicinity of the Baltic Sea,” adds Dr. Timothy White of NOAA’s Biogeography Branch, an expert on sea duck foraging. “It is gratifying to see how meticulous fieldwork, focused on behavioral observations and prey analysis, is continuing to broaden our understanding of community patterns, seabird feeding ecology and social interactions.”

Newly demonstrated foraging method of Herring Gulls and Mew Gulls with benthivorous diving ducks during the nonbreeding period is available at http://www.aoucospubs.org/doi/abs/10.1642/AUK-15-62.1.

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. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.