Terns Face Challenges When They Fly South for Winter

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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.

Long-Term Study Reveals Fluctuations in Birds’ Nesting Success

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Long-term data on Song Sparrows reveals factors that affect their nesting success. Photo credit: D. Janus

Understanding the factors that affect a bird species’ nesting success can be crucial for planning effective conservation efforts. However, many studies of nesting birds last only a few years—and that means they can miss the effects of long-term variation and rare events. A new study from The Auk: Ornithological Advances demonstrates this with nearly four decades of data from Song Sparrows in British Columbia.

The University of British Columbia’s Merle Crombie and Peter Arcese used 39 years of data from an island population of Song Sparrows to examine how the factors influencing their nesting success changed over long periods of time. Over almost 3,000 nesting attempts, 64% of which were successful, a number of patterns emerged. Some, such as the fact that older female birds were less successful, remained consistent over time. However, others, such as the effects of rainfall, population density, and nest parasitism, interacted with each other in complex ways that caused their importance to wax and wane over the decades, and inbreeding only became a significant negative factor when it increased sharply during the middle portion of the study. Unpredictable, rare fluctuations such as this can have large effects that shorter-term studies rarely capture.

“Researchers have been learning about the Song Sparrow population on Mandarte Island since 1960, and monitoring the population continuously since 1975,” says Arcese. “Because the population is semi-isolated, small, and resident year-round, we band all birds in the nest and have genotyped all nestlings since 1991.” A close focus on individuals, fitness, and relatedness in the Mandarte Song Sparrow population has allowed researchers to report the most precise demographic and population genetic parameters yet estimated in wild populations.

“Most studies of plant and animal populations in nature last three to five years, but ecological processes are often dramatically affected by climate and community change, which plays out over decades,” he continues. “Long-term studies like ours provide an invaluable record of change in population processes, which can help interpret the results of short-term studies of species not as easily studied as Song Sparrows.”

Temporal variation in the effects of individual and environmental factors on nest success is available at http://www.bioone.org/doi/full/10.1642/AUK-17-189.1.

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.

Scientists Remind Their Peers: Female Birds Sing, Too

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Northern Cardinals are among the familiar North American bird species in which females sing in addition to males.

When North American ornithologists hear a bird singing, they’re likely to assume it’s a male. But in many species, the females sing too—and a new commentary in The Auk: Ornithological Advances argues that a better understanding of these unappreciated female songs could lead to advances in many aspects of bird biology.

Authors Karan Odom of Cornell University and Lauryn Benedict of the University of Northern Colorado both discovered the world of female birdsong through their own research. “I started studying California towhees 17 years ago, and I was fascinated by the duet vocalization given by females and males,” says Benedict. “That led me to start looking for female song in other North American bird species, and I was surprised to learn that it was much more common than I expected. The reports of female song are buried in odd corners of the literature, but when you put them all together, you start to see some interesting patterns.”

Though singing females were likely the norm among the ancestors of today’s songbirds, female song today is understudied and is underrepresented in collections of bird sound recordings. This, say Odom and Benedict, may be result of bias toward the world’s temperate regions—though more widespread in temperate species than many ornithologists appreciate, female song is most common among tropical birds. They argue that better documentation of which species female song is present in and more detailed descriptions of female song structure and output could improve our understanding of birds’ comparative physiology, neurobiology, behavioral ecology, evolution, and even conservation. Birds of conservation concern are often located and identified by song during surveys, and assumptions that all singing birds are male could mislead wildlife managers about the state of populations.

Odom and Benedict urge their fellow ornithologists to spread the word that female birds sing, to share resources, and to disseminate their findings. You don’t need to be a professional ornithologist in order to help expand our knowledge of female song, either—Odom has created a website where any birdwatcher can upload their observations. “If you hear a bird singing, do not assume it’s a male,” she says. “If you observe a female bird singing, document it by uploading field notes, audio, or video to the collections on our website, femalebirdsong.org. Make sure to indicate how you recognized the bird was female.”

“Odom and Benedict have written an excellent appeal to document and record more female bird song,” adds Leiden University’s Katharina Riebel, a former collaborator of Odom’s. “They rightly point out that the extent of female bird song has been starkly underestimated, as almost by default we assume that a singing bird must be the male of the species. As a consequence, we might have missed out many aspects and the dynamics of male and female vocal signaling in songbirds—clearly, there is still lots to discover! I am confident that ornithologists in the field can make substantial contributions toward these questions by sharing their observations and recordings, as I very much hope this article will encourage them to do.”

A call to document female bird songs: Applications for diverse fields is available at http://www.bioone.org/doi/full/10.1642/AUK-17-183.1.

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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Long Incubation Times May Defend Birds Against Parasites

Some tropical birds have longer egg incubation times than their temperate cousins, even though their habitat is teeming with egg-eating predators. The reason why has long been a mystery, but a new study from The Auk: Ornithological Advances applies new methods to confirm the evidence for an old hypothesis—that a longer development period leads to a stronger, more efficient immune system.

The University of Missouri-St. Louis’s Robert Ricklefs first studied this relationship in the early 1990s, using data from microscopic examination of avian blood samples for the presence of parasites, primarily those that cause malaria. He found that the longer a species’ incubation period, the lower its prevalence of parasites. However, Ricklefs remained concerned that especially low parasite loads could have been missed during microscope examination, affecting parasite prevalence estimates.

Advances in DNA sequencing offered a new solution. For their new study, Ricklefs and his colleagues collected blood samples from birds in the eastern U.S. and several Neotropical countries and checked for the presence of parasite DNA, tabulating how many individuals from various families of birds were sampled at each site and how many were infected with Haemoproteus or Plasmodium parasites. About 22% of individual birds in both temperate and tropical regions had parasite DNA in their blood. While incubation time varies little among temperate species, it does vary among tropical species, and in tropical birds parasite prevalence was significantly lower in species with longer incubation times.

These results confirm those of the old blood smear analysis. While there is still no direct evidence for the hypothesis that a longer incubation time promotes a stronger immune system, this correlation provides a strong hint that this could indeed be the solution to the mystery of why the embryos of some tropical birds take so long to develop. “My interest in blood parasites was stimulated by a former graduate student, Victor Apanius, primarily in the context of community ecology. However, I had been working on the diversification of avian life histories, particularly embryo and chick growth rates, and I couldn’t help but notice a connection between the two,” says Ricklefs. “I wasn’t surprised that the new results confirm the old ones so well, really, because the two techniques estimate the same attribute. However, more detailed studies of the avian immune response and how variation in host defense is related to development certainly are warranted.”

“This paper is a nice follow up the 1992 study that showed an inverse relationship between parasite prevalence and egg incubation period. Since that time, PCR methods have been developed that detect more infections than microscopy, and the work is important because it verifies the previous results with revised methods,” according to San Francisco State University’s Ravinder Sehgal, an expert on avian blood parasites who was not involved in the study. “Moreover, it renews interest in a phenomenon that has gone largely unexplored. It will be now be important to test the work in an experimental system, to study the parasitology and explore the tradeoffs between embryo growth rate and immune function.”

Duration of embryo development and the prevalence of haematozoan blood parasites in birds is available at http://www.bioone.org/doi/full/10.1642/AUK-17-123.1.

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.

Are Flamingos Returning to Florida?

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American Flamingos should be considered native to Florida, argue the authors of a new review. Photo credit: J. Patterson

Flamingos are a Florida cultural icon, and sightings of American Flamingos in the state have been on the rise in recent decades. However, whether they’re truly native to the U.S. or only arrive via escape from captivity has long been subject to debate, making developing a plan for managing Florida’s flamingo population challenging. A new study from The Condor: Ornithological Applications reviews the evidence and provides a fresh argument that the birds should be considered part of the Sunshine State’s native fauna.

Zoo Miami’s Steven Whitfield, along with colleagues from Audubon Florida’s Everglades Science Center, the National Park Service, Big Cypress National Preserve, and the Rookery Bay Estuarine Research Reserve, reexamined the historical evidence of flamingos in Florida and evaluated the likely origins of birds seen in recent years. Overall, they conclude, the evidence from both narrative accounts and museum records suggests that American Flamingos once occurred naturally in large flocks in Florida and probably even nested there before being eliminated by hunting around 1900. From 1950 to the present, however, birdwatchers have reported almost 500 new observations of flamingos in Florida, with both flock size and the frequency of observations increasing over time. While it’s plausible that some of these individuals could be escapees from captive flocks, there is also strong evidence for dispersal from wild populations in Mexico and the Caribbean.

The population history Whitfield and his coauthors describe is consistent with that of some native species already protected by state and federal endangered species laws, and they hope that their study will lead to a better plan for managing wild flamingos in Florida. “Living in Florida, you see flamingos everywhere—in advertising, in place names, even on the logo for the state lottery—but as an actual organism, as a species, there was essentially no information available on the biology of flamingos,” says Whitfield. “Some biologists considered them native birds that were extirpated during the plume trade of the late 1800s, and urged for population recovery measures, while others considered the rare flamingos seen around Florida to be escapes from captive colonies. We often say that in south Florida we have just two types of species, introduced and endangered, but a species can’t be both at the same time.”

“This article finally sheds welcome light on status of these iconic birds in Florida. The authors meticulously researched historic records and compiled more recent sightings to reconstruct the history and population trends of flamingos in Florida,” adds the American Museum of Natural History’s Felicity Arengo, a flamingo conservation expert who was not involved in the study. “Flamingo numbers have increased notably since the 1950s due to protections to species and habitats in Florida and throughout the Caribbean. The authors are cautious and recognize the limitations of the data in their study, but they provide ample evidence that Florida was the northernmost extent of the American Flamingo prior to the early 1900s and that populations have been recovering.”

Status and trends of American Flamingos (Phoenicopterus ruber) in Florida, USA is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-187.1.

About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology. It began in 1899 as the journal of the Cooper Ornithological Club, a group of ornithologists in California that became the Cooper Ornithological Society, which merged with the American Ornithologists’ Union in 2016 to become the American Ornithological Society. In 2016, The Condor had the number one impact factor among 24 ornithology journals.

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Fracking Tied to Reduced Songbird Nesting Success

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A researcher handles a Louisiana Waterthrush chick. Photo credit: M. Frantz

The central Appalachian region is experiencing the country’s most rapid growth in shale gas development, or “fracking,” but we’ve known almost nothing about how this is affecting the region’s songbird populations—until now. A new study from The Condor: Ornithological Applications demonstrates that the nesting success of the Louisiana Waterthrush—a habitat specialist that nests along forested streams, where the potential for habitat degradation is high—is declining at sites impacted by shale gas development in northwestern West Virginia.

West Virginia University’s Mack Frantz and his colleagues mapped waterthrush territories and monitored nests along 14 streams from 2009 to 2011 and again from 2013 to 2015. They also mapped and measured disturbances to streams and to the forest canopy, using aerial photographs and satellite imagery as well as extensive ground-truthing, and classifying them according to whether they were related to shale gas development. Their results show that as shale gas development has expanded in the area, nest survival and productivity and riparian habitat quality have declined. At the same time, the size of individual waterthrush territories has increased, suggesting birds need to range farther to find sufficient resources. This study is one of the first to demonstrate that shale gas development can affect songbird reproductive success and productivity, both directly through the presence of fracking infrastructure and indirectly through effects on habitat quality.

“I hope our findings lead to robust protections of our forested headwater stream ecosystems, which are currently overlooked for regulation despite their critical role in providing nutrients and organic matter downstream, not to mention as an important source for drinking water,” says Frantz. “Waterthrushes are a modern-day ‘canary in the coal mine,’ and there are many more opportunities to study how anthropogenic disturbance affects and entangles food webs at the aquatic–terrestrial interface.”

“After twelve years of research conducted with this species, I have seen the numerous impacts hydraulic fracturing has had on waterthrush survival and the toll that the industry has had on our nation’s wild places and wildlife,” adds Louisiana State University-Alexandria’s Leesia Marshall, a waterthrush expert who was not involved in the Condor study. “This paper should serve as a call for all scientists to redouble efforts across all related disciplines to document the present impacts of shale gas extraction and to develop strategies for mitigation and avoidance of potential impacts in the future.”

Demographic response of Louisiana Waterthrush, a stream obligate songbird of conservation concern, to shale gas development is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-130.1.

About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology. It began in 1899 as the journal of the Cooper Ornithological Club, a group of ornithologists in California that became the Cooper Ornithological Society, which merged with the American Ornithologists’ Union in 2016 to become the American Ornithological Society. In 2016, The Condor had the number one impact factor among 24 ornithology journals.

Warming Temperatures May Cause Birds to Shrink

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The size of adult House Sparrows is predicted by maximum temperatures during development. Photo credit: P. Deviche

Biologists have known for a long time that animals living in colder climates tend to have larger bodies, supposedly as an adaptation to reduce heat loss. However, understanding how temperature affects animals has gained new importance thanks to climate change. A new study from The Auk: Ornithological Advances uses European House Sparrows, which have spread into a variety of climates in Australia and New Zealand since their introduction in the mid-19th century, to show that this trend in birds might actually be due to the effects of high temperatures during development—raising new alarms about how populations might be affected by global warming.

Macquarie University’s Samuel Andrew and his colleagues captured and measured approximately 40 adult House Sparrows at each of 30 locations across Australia and New Zealand. They found that maximum temperatures during the summer, when the birds breed, were a better predictor of adult body size at each location than winter minimum temperatures. This adds support to the idea that excessive heat during development may affect birds’ growth throughout their lives, raising concerns that increasing summer temperatures due to climate change could drive down the average adult body size, with potential effects on the birds’ fitness.

“If variation in body size is linked directly or indirectly to adapting to different climates, then body size could be useful for monitoring the extent to which bird populations are capable of adapting rapidly to changing climates,” says Andrew. “Our work on this common species helps us to understand the adaptive responses of birds to a changing climate and their constraints, and this fundamental knowledge will help future workers and managers focus their work on other species and potentially identify those species most at risk from climate change.”

“This paper is an important addition to a growing body of work that is changing our understanding of the relationships between climate and body size. The big question generated by these results is the extent to which the observed relationship is the outcome of adaptive evolutionary differences among sites as opposed to direct developmental responses to different temperatures. Interestingly, some of these same authors just published experimental evidence for a direct effect of temperature on growth in another bird species,” adds Whitman College’s Tim Parker, an expert who was not involved with the research. “This is not a new idea, but it has been largely ignored by those who have assumed that most morphological variation in birds is due to evolved adaptive variation. We need more work on the direct effects of temperature variation on development in endotherms.”

Clinal variation in avian body size is better explained by summer maximum temperatures during development than by cold winter temperatures is available at http://www.bioone.org/doi/full/10.1642/AUK-17-129.1.

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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