How Many Golden Eagles Are There?

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Photo credit: D. Brandes

For conservation efforts to be effective, wildlife managers need to know how many individuals of a species are out there. When species are spread out over large areas and occur at low densities, as is the case with the Golden Eagle, figuring this out can be tricky. However, a new study from The Condor: Ornithological Applications applies an old technique called “mark-recapture” in a novel way, eliminating the need to actually capture and mark eagles but instead, using math that allows scientists to turn individual observations into population estimates.

West Virginia University’s Andrew Dennhardt, Adam Duerr, and Todd Katzner and Lafayette College’s David Brandes used observations made by volunteer “citizen-scientists” of Golden Eagles migrating along a single, long mountain ridgeline in Pennsylvania to estimate the total number of eagles passing through the area each year. To do this, they developed a new way to apply a classic ecology tool called mark-recapture analysis—capturing and marking a portion of a population, and then counting the number of marked individuals in another group captured later. Helped by the fact that observers were often able to categorize individual eagles as either immature or adult birds, the scientists were able to identify instances of individual eagles being sighted at more than one location as they made their way south along the ridge over the course of a day, treating these subsequent sightings as “recaptures.”

Volunteers reported more than 3,000 sightings of Golden Eagles at five count sites along the ridge from 2002 to 2011. The analysis used in the study, which lets researchers estimate how many birds were missed as well as how many were seen more than once, suggests that these sightings represented between 2,592 and 2,775 individual eagles over the ten year period, with approximately 1,300 passing through the area on average in a given year. Past studies indicate that the total population of eagles breeding in Quebec and migrating through Pennsylvania is around 5,000, making this about a quarter of the larger population. Because the eagles are difficult to count on their breeding grounds, however, better methods for tracking their numbers during migration represent a significant advance.

“Conservation of Golden Eagles in eastern North America is a really important goal for lots of reasons—it is a small, historically declining population, at risk from anthropogenic threats and habitat loss. A central part of that conservation goal is figuring out how many of the darn things there are. Andrew’s work is the first empirical estimate of golden eagle population size,” says Katzner, now a Research Wildlife Biologist at the US Geological Survey. “Nothing quite like this has ever been done. We’ve taken a standard tool, mark–recapture, and turned it on its head to give us a new way to estimate population size.”

“For me, this was a dream come true, because I got to work on a project relevant to the conservation of the species that originally inspired me to enter the field of wildlife ecology and management,” says Dennhardt, now at Michigan State University. “Partnerships between researchers and citizen-scientists can help improve wildlife management decisions to address threats to migratory Golden Eagles and other species. I hope this work inspires future researchers to evaluate the populations of other migratory species, and that it encourages the greater scientific community to consider new and existing citizen-science programs and think about how such programs’ data might be used in their own research toward improving resource management and decision making.”

Applying citizen-science data and mark–recapture models to estimate numbers of migrant Golden Eagles in an Important Bird Area in eastern North America is available at http://www.bioone.org/doi/full/10.1650/CONDOR-16-166.1.

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.

Grassland Sparrows Constantly Searching for a Nicer Home

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A Grasshopper Sparrow with a radio transmitter. Photo credit: E. Williams

Some birds regularly move to new territories between years, depending on factors including habitat quality and the presence of predators, but what about within a single breeding season? Grassland ecosystems are particularly dynamic, continuously shaped by fire and grazing, and a new study from The Auk: Ornithological Advances confirms that one particular grassland bird moves frequently each summer in search of the best territories. For Grasshopper Sparrows, the grass really does look greener on the other side.

Emily Williams and Alice Boyle of Kansas State University captured 647 male Grasshopper Sparrows over the course of three breeding seasons and marked them with identifying color bands, surveying territories weekly to track their movements. The results indicate that about 75% of males changed territories at least once per season, with a third of banded defending new territories at least 100 meters away from where they were originally sighted. Additionally, 9 of 19 birds fitted with radio transmitters established new territories as far as 1200 meters away from their original locations.

“We had many plots where the density remained relatively stable over the entire breeding season, which could appear as if individual birds remained settled in the same areas over time. However, what we found was the complete opposite—individuals were blinking in and out of territories the entire time,” says Williams, who has since moved on to a position at Denali National Park and Preserve. “So while an onlooker could see a male Grasshopper Sparrow singing on a single patch of ironweed for months at a time, the identity of the individual claiming that ironweed as his own could change two or three times in a single summer.” Without careful observations, researchers could completely miss these dynamic movements happening over the course of a season.

This high turnover implies that while some birds might perceive a patch of habitat as no longer suitable, others see the same area as a good place to settle, perhaps because they base decisions on their individual experiences of nest success or failure. High mobility may benefit grassland birds by helping them locate isolated patches of high-quality habitat and colonize newly created or restored habitat, but could also challenge researchers’ ability to accurately track survival over time.

“Many avian ecologists have probably anecdotally noticed within-season shifts in breeding territories, yet this is one of the first attempts to actually quantify this phenomenon. The extent to which territorial turnover occurred and the fairly extensive distances moved by males within a season are intriguing!” says the University of Wyoming’s Anna Chalfoun, an expert on grassland birds who was not involved in the study. “I am left wondering if this behavior is more common than ornithologists have previously acknowledged and what drives proximate shifts in breeding territories. The results certainly have implications for habitat management for territorial birds of concern and for the accuracy of survival and site fidelity analyses.”

Patterns and correlates of within-season breeding dispersal: A common strategy in a declining grassland songbird is available at http://www.bioone.org/doi/full/10.1642/AUK-17-69.1.

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.

Safety, Not Food, Entices Geese to Cities

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Radio transmitter data has revealed the real reason geese hang out in cities. Photo credit: M. Horath

Canada Geese have shifted their winter range northward in recent years by taking advantage of conditions in urban areas—but what specific features of cities make this possible? A new study from The Condor: Ornithological Applications suggests that rather than food, geese are seeking safety, congregating in areas where they can avoid hunters and be buffered from the coldest winter temperatures.

Heath Hagy of the University of Illinois at Urbana–Champaign and his colleagues captured 41 geese in the Greater Chicago Metropolitan Area between 2014 and 2016 and fitted them with radio transmitters to track their movements. While the geese used a remarkable variety of urban habitats, they preferred deep water and rivers over green space such as parks when temperatures dropped enough to tax their ability to maintain their body temperature. For geese that remained within the metropolitan area, winter survival was 100%, but this dropped to 48% for those that emigrated out to forage in surrounding agricultural fields, countering expectations that the proximity of agricultural habitat may be a factor in geese’s winter expansion in the area. Together, these results suggest that sanctuary may be a higher priority for wintering geese than good foraging habitat.

Better understanding how geese use urban habitat in winter may help reduce human–wildlife conflicts such as collisions with airplanes. “The growth of urban areas and northward expansion of row-crop agriculture have changed the way geese migrate. Unfortunately, some of our large cities have become goose sanctuaries, where resident geese and migratory geese congregate during winter to escape hunting pressure,” says Hagy. “Although additional research is needed, our data will be useful to guide goose harassment efforts, which may offset the benefits of remaining inside urban areas during winter and open hunting seasons.”

“This work offers comprehensive insights into the biology and behavior of a large wintering population of Canada geese that inhabits a major metropolitan area in the mid-western U.S. Appropriately grounded in an energetic context, the study thoroughly describes how Canada geese utilize the urban environment under varying weather conditions and demonstrates the survival benefits of urban adaptation,” according to The Ohio State University’s Robert Gates, a wildlife management expert who was not involved in the research. “Findings from this study provide a firm biological grounding for the development and implementation of management actions to alleviate human–Canada goose conflicts in urban areas.”

Survival and habitat selection of Canada Geese during autumn and winter in metropolitan Chicago, USA is available at http://www.bioone.org/doi/abs/10.1650/CONDOR-16-234.1.

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. The Condor had the top impact factor among ornithology journals for 2016.

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Songbird Populations May Indicate Trouble in Northwestern Forests

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Purple Finches, an indicator of healthy coniferous habitat, are declining in the Northwest. Photo credit: J. Livaudais

Populations of many North American songbirds are declining, and in many cases we don’t understand why—for example, whether the problem lies with reproductive success or in the survival rates of adults. Conservation efforts need this information to be effective, and bird banding stations can help fill in the gaps, providing insights into how demographics vary across space and time. A new study from The Condor: Ornithological Applications presents ten years of data from banding stations across northern California and southern Oregon and offers new hints on what’s driving changes in the region’s songbird populations.

The Klamath Bird Observatory’s Sarah Rockwell and her colleagues used data collected at ten of the observatory’s bird banding sites between 2002 and 2013 to estimate the abundance and reproductive productivity of twelve songbird species, all either of regional conservation concern or indicators of coniferous or riparian habitat quality. They found that three species (the Purple Finch, Yellow-rumped Warbler, and Dark-eyed Junco), all indicators of coniferous habitat, were declining across the region, while two (the Yellow-breasted Chat and Black-headed Grosbeak) were increasing, though the trends varied from site to site. While breeding productivity declined in three species, adult abundance was correlated with the previous year’s productivity for only one species, the Yellow Warbler, suggesting that local productivity is not the primary culprit behind population declines.

“Before we can understand the impact of threats to bird populations, we first need to understand what’s happening where,” says John Alexander, the Executive Director of the Klamath Bird Observatory and a coauthor on the work. “This study presents trends from regional-scale monitoring and just begins to scratch the surface of understanding population dynamics, variation in demographic rates, and drivers of population change across our landscape, which is vital information for developing effective conservation plans. It also highlights concerns about forest-associated species in this region—the need to balance timber harvest, a mixed-severity fire regime, and endangered species management continue to present complex conservation challenges.”

“We have been so lucky to consistently get awesome field crews—we host six to ten interns each year, and they travel all over the Klamath-Siskiyou bioregion, camping regularly throughout the field season. We have had interns from more than seventeen different countries, and they all receive extensive training and work very hard,” adds Rockwell. “This work is so important. We need robust baseline data if we are going to be aware of any kind of population change, let alone be able to do something about it!”

Spatial variation in songbird demographic trends from a regional network of banding stations in the Pacific Northwest is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-44.1.

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, 2.654.

About Klamath Bird Observatory: Based in Ashland, Oregon, KBO is a scientific non-profit organization that achieves bird conservation in the Pacific Northwest and throughout the migratory ranges of the birds of our region. Emphasizing high caliber science and the role of birds as indicators of the health of the land, KBO specializes in cost-effective bird monitoring and research projects that improve natural resource management. Also, recognizing that conservation occurs across many fronts, we nurture a conservation ethic in our communities through our outreach and educational programs.

A First Look at Geographic Variation in Gentoo Penguin Calls

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A calling Gentoo Penguin. Photo credit: M. Lynch

Vocal communication is central to the lives of many birds, which use sound to attract mates and defend territories. Penguins are no exception, but we know little about how or why penguin vocalizations vary geographically between isolated populations. A new study from The Auk: Ornithological Advances takes a broad look at vocalizations across the range of Gentoo Penguins and concludes that while their calls do vary from place to place, we still have a lot to learn about the processes at work.

The Gentoo Penguin’s “ecstatic” call, consisting of repeated pairs of short syllables, is used to attract and contact mates. Maureen Lynch and her PhD advisor Dr. Heather Lynch (no relation) of Stony Brook University recorded ecstatic calls at 22 Gentoo Penguin colonies across the Antarctic Peninsula, southern Argentina, and nearby islands. While they found variation in call frequency and duration both within and between colonies, no clear patterns emerged based on latitude, region, or subspecies. An algorithm based on their data was able to classify calls to correct colonies better than random, but with a high error rate.

Their results suggest that the vocal characteristics of colonies drift independently of each other over time. Within colonies, it may be beneficial for individuals to differ in their calls so that they can tell each other apart. “There is so much that we still do not know about penguin vocal behavior,” says Heather. “We see this as being very much the beginning, rather than the end, of understanding how penguins communicate, how and if such communications play a functional role in protection against predators, choice of mates, and breeding site selection.”

“Work in the Antarctic is always challenging, and this project was time- and data-intensive, with data collection over three field seasons,” adds Maureen. “Unexpected challenges came from flying birds rather than penguins. The recording units hold up well in the Antarctic elements and can even record over winter, but I learned the hard way that if I leave a Song Meter unattended in the Falkland Islands, the Striated Caracaras will eat the windscreens off the microphones and can actually pull the microphones off.”

“Understanding the drivers of population differentiation is increasingly important for species such as penguins that are being impacted by climate change,” according to Fordham University’s J. Alan Clark, a penguin behavior researcher who was not involved in the study. “This study, the largest of its kind, takes a creative and rigorous approach to exploring the role of vocalizations in population differentiation across a wide geographic range and across populations with known intraspecific genetic variation. The results of this study provide practical insights that help set the stage for future research on interactions between speciation processes and climate change.”

Variation in the ecstatic display call of the Gentoo Penguin (Pygoscelis papua) across regional geographic scales is available at http://www.bioone.org/doi/full/10.1642/AUK-17-4.1.

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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Could Condors Return to Northern California?

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A study of lead exposure indicates condors could one day return to Northern California. Image credit: C. West

In 2003, Northern California’s Yurok Tribe initiated efforts to reintroduce California Condors on their lands. While wild condors have not existed in the region for more than a hundred years, a new study from The Condor: Ornithological Applications suggests that hunters transitioning from lead to non-lead ammunition may allow these apex scavengers to succeed there once again.

Lead, which condors consume when scavenging at carcasses of animals killed with lead ammunition, is the main factor limiting their recovery; lead toxicosis was responsible for 26% of juvenile condor deaths and 67% of adult condor deaths between 1992 and 2009. To assess condor’s prospects in Northern California, Chris West of the Yurok Tribe Wildlife Program and his colleagues trapped two other avian scavengers, Turkey Vultures and Common Ravens, at nine sites in the region between 2009 and 2013. Collecting blood samples from 137 vultures and 27 ravens, they found that lead levels in ravens were almost six times higher during hunting season, when they were exposed to animal remains tainted with lead ammunition, than the rest of the year. Vulture’s migratory movements meant they couldn’t be sampled across seasons, but older vultures tended to have higher concentrations of lead, suggesting that older, more dominant individuals exclude younger birds from foraging on carcasses.

While this may sound like bad news, it means little stands in the way of condor recovery if hunters shift away from using lead ammunition in the region. A statewide ban on lead ammunition in California takes effect in 2019, and West and his colleagues are optimistic that it may lower lead exposure to scavengers if it includes outreach programs to help the state’s hunting community through the transition. “Our hopes for condor reintroduction to our area and recovery overall is very high. We are currently going through the National Environmental Policy Act (NEPA) process to select release locations and assess and mitigate impacts to land owners and managers in the region,” says West. “The return of condors to the Pacific Northwest, after more than a century-long absence, will be a testament to the ability of federal, tribal, state, and private entities to come together to champion the cause of wildlife, ecosystem, and cultural recovery in our region.”

“Northern California still has viable habitat for free-flying California Condors, and these results suggest it is possible to succeed in this region, particularly as a broader switch from lead to non-lead ammunition use is realized,” adds to Kelly Sorenson, Executive Director of the Ventana Wildlife Society and an expert on condor recovery who was not involved in the study. “If we fix the lead problem, condors should survive in the wild again without the assistance of people, whether in Northern California or other suitable locations where they are being released.”

Feasibility of California Condor recovery in northern California, USA: Contaminants in surrogate Turkey Vultures and Common Ravens is available at http://www.bioone.org/doi/abs/10.1650/CONDOR-17-48.1.

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. The Condor had the top impact factor among ornithology journals for 2016.

Social Environment Matters for Duck Penis Size

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Penis size in Ruddy Ducks has a complex relationship with the birds’ social environment. Image credit: P. Brennan

Most birds lack genitalia, but male ducks are known for their long, spiraling penises, which have evolved through an ongoing cat-and-mouse game with females. A new study from The Auk: Ornithological Advances looks at whether these impressive organs are affected by the social environment—that is, whether male ducks that face more competition grow bigger penises. While this appears to be true for some species, in others the relationship between social environment and penis growth is more complex.

Patricia Brennan of Mount Holyoke College and her colleagues tested their hypothesis in two species: Ruddy Ducks, which are very promiscuous, do not form pair bonds, and have relatively long penises, and Lesser Scaup, which form seasonal pair bonds and have relatively short penises. Keeping captive ducks in either pairs or groups during the breeding season over two years, they found that Lesser Scaup had longer penises on average when housed in groups with other males, as predicted. For Ruddy Ducks, the effects were more complicated—many males failed to reach sexual maturity until the second year of the experiment, and when they did, the smaller Ruddy Duck males housed in groups grew their penises faster than males housed in pairs, but grew out of sync with each other and stayed in reproductive condition for only short periods of time.

Small Ruddy Ducks males faced with intense competition may strategically offset their development from each other to reduce the costs of male–male aggression and make the best of a bad situation. Additionally, since Ruddy Ducks already have relatively long penises on average compared to other waterfowl species, their ability to grow even larger based on social cues may be limited. In any case, the study shows that the level of competition that individual male ducks experience can have a big effect on their genitals.

The biggest challenge during the study, says Brennan, wasn’t measuring the ducks—it was simply keeping them housed and fed. “Keeping ducks in captivity is expensive,” says Brennan. “We were lucky to partner with the Livingstone Ripley Waterfowl Conservancy in Litchfield, Connecticut, where their expert personnel kept the ducks healthy and in beautiful, naturalistic enclosures year-round.”

“This is an excellent experimental study of penis morphology, looking at the effects of social environment on penis size in two duck species that have different mating systems,” according to Queen’s University’s Bob Montgomerie, an expert on reproductive strategies who was not involved in the study. “The question now is whether the observed increase in penis size in Lesser Scaup under the threat of sperm competition actually gives males a competitive advantage. Like all good studies, this one will undoubtedly stimulate more research, as it provides both methodologies and a clear focus on interesting questions.”

Evidence of phenotypic plasticity of penis morphology and delayed reproductive maturation in response to male competition in waterfowl is available at http://www.bioone.org/doi/full/10.1642/AUK-17-114.1.

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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