Monitoring Birds by Drone

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Researchers test the bird monitoring drone. Photo credit: A. Wilson

Forget delivering packages or taking aerial photographs—drones can even count small birds! A new study from The Auk: Ornithological Advances tests this new approach to wildlife monitoring and concludes that despite some drawbacks, the method has the potential to become an important tool for ecologists and land managers.

Bird surveys provide crucial data for environmental management, but they have limitations—some areas are difficult to access, and surveyors vary in their skills at identifying birds. Using audio recordings made by unmanned aerial vehicles (UAVs) can help to combat both of these pitfalls, as hard-to-reach sites can be flown over and multiple people can review the resulting recordings. Andrew Wilson of Gettysburg College and his colleagues tested the feasibility of this approach by using fishing line to suspend an audio recorder from a simple “drone,” first in trial runs on college athletic fields and then in real bird surveys on Pennsylvania State Game Lands.

The experiments on state game lands directly compared UAV data with traditional ground-based surveys of the same areas. A few bird species were undercounted by the UAV technique, such as Mourning Doves, whose extremely low-frequency calls weren’t picked up by the recorder, and Gray Catbirds, which occurred at such high densities that counting individual birds in the recordings was difficult. Overall, however, there were few significant differences between the results produced by the two methods.

“The inspiration for the study came while I was surveying forests in the Appalachian Mountain in Pennsylvania for Cerulean Warblers,” says Wilson. “All of our survey work was done from roadsides or hiking trails, for logistical reasons and to maximize survey efficiency, but I was always aware that our sample locations were very biased and that we were missing key areas such as steep forested slopes.” He notes that the drone and audio recorder used in this experiment were inexpensive, commercially available models, making this technique within reach even for those with limited funding.

“I recall my vocal reaction upon hearing their oral presentation during a session I chaired on emerging technologies to study birds at the 2016 North American Ornithology Conference last August, where I exclaimed, ‘What an amazingly simplistic but useful application of a drone for bird research—I wish I had thought of it!’” says McGill University’s David Bird, founding editor of the Journal of Unmanned Vehicle Systems. “This unique study provides a significant first step toward the inevitable common use of unmanned vehicle systems for monitoring songbird populations both during the breeding season and on migration.”

The feasibility of counting songbirds using unmanned aerial vehicles is available at http://americanornithologypubs.org/doi/full/10.1642/AUK-16-216.1.

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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AUTHOR BLOG: How Will an Arctic-Breeding Songbird Respond to Taller Shrubs and Warmer Temperatures?

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A female Smith’s Longspur solicits a mate. Photo credit: J. Hughey

Heather McFarland

Linked paper: Nest-site selection and nest success of an Arctic-breeding passerine, Smith’s Longspurs, in a changing climate by H.R. McFarland, S. Kendall, and A.N. Powell, The Condor: Ornithological Applications 119:1, February 2017.

How will songbirds that nest in tundra respond as the Arctic transforms into a warmer and shrubbier environment? This is the question that drove us to study a small songbird known as the Smith’s Longspur. Endemic to North America, this songbird breeds in only a few remote mountain valleys in Canada and Alaska, making it particularly susceptible to changes at northern latitudes. Smith’s Longspur’s are also unique in that they are polygynandrous. This is a rare mating strategy where both sexes are polygamous, and birds of either sex may mate with up to three individuals each breeding season. Rather than a single male and female establishing a territory, Smith’s Longspurs usually form larger groups called neighborhoods which contain many inter-mated individuals. Since this mating strategy is poorly understood and so different from other tundra nesting songbirds, it is difficult to predict how breeding Smith’s Longspurs may respond to climate change. Therefore, prior to further change, baseline information about breeding requirements is needed.

To fill this void, we monitored more than 250 Smith’s Longspur nests between 2007 and 2013 in the Brooks Range of Alaska. All of the nests were found in open tundra areas, and females never placed their nests in tall vegetation. Aside from a lack of tall shrubs, no specific habitat features that we measured influenced where females placed their nests. This finding is contrary to patterns commonly observed in monogamous ground-nesting birds where females tend to nest near a specific habitat feature. We believe that Smith’s Longspurs may deviate from this pattern because of their unique breeding strategy. Females may benefit more by nesting near other females where the chance of “hooking up” with additional males is greater. If this is the case, nest site selection may occur at a larger neighborhood scale. Considering these findings, we are concerned that future shrub growth in the Arctic could limit the amount of open tundra areas available for breeding neighborhoods of Smith’s Longspurs.

Although there may be fewer available nest sites in the future, warmer temperatures could benefit breeding Smith’s Longspurs. In this study, nests survived best when there were more warm days during the nesting period. Cold temperatures appeared to have no impact on nest success, possibly because females were able to delay nesting until weather conditions were favorable. During these years, females usually began nesting within a few days of one another, compared to years with good conditions early in the season when egg laying was spread out over several weeks. Considering that Smith’s Longspurs breed in the Arctic, it is not surprising that they have adapted strategies to withstand harsh conditions. Because of this adaptive ability, as well as the predicted increase in temperature throughout the Arctic, we believe that breeding Smith’s Longspurs could become more productive in the future. Even so, the combined outcome of reduced suitable habitat but potentially higher breeding productivity is still unknown. Continued monitoring of Smith’s Longspurs is needed as northern regions continue to change.

AUTHOR BLOG: Population-Specific Migration Patterns of Golden-Winged Warblers

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Gunnar Kramer

Linked paper: Nonbreeding isolation and population-specific migration patterns among three populations of Golden-winged Warblers by G.B. Kramer, H.M. Streby, Sean M. Peterson, J.A. Lehman, D.A. Buehler, P.B. Wood, D.J. McNeil, J.L. Larkin, and D.E. Andersen, The Condor: Ornithological Applications 119:1, February 2017.

Our study in The Condor: Ornithological Applications follows decades of research on the population dynamics of a declining songbird species, the Golden-winged Warbler.

Golden-winged Warblers have long been the focus of research and conservation interest due in part to sensationalized range-wide declines on the order of -2.5% per year; however, the true nature of these declines is more nuanced and complicated. When geographic populations are considered, Golden-winged Warblers demonstrate two very different stories. On one hand, the Appalachian population, breeding from Ontario through North Carolina and Georgia, experienced severe declines (up to -7% per year) over the past 50 years resulting in local extirpations and noticeable declines in the abundance and distributions of Golden-winged Warblers in the region. On the other hand, the western Great Lakes population, breeding largely in Minnesota, is home to ~50% of the global breeding population of Golden-winged Warblers and is maintaining historic population levels or possibly increasing over the past 50 years. When combined, these two very different stories blend into a general picture of overall population decline, spawning intensive efforts to identify breeding-grounds factors that might explain this decline, such as the loss of nesting habitat, poor nesting success, and competition with other closely related species (i.e., Blue-winged Warblers). Despite all the extensive research, no single breeding-grounds factor or combination of factors provides a parsimonious and consistent explanation for the differential population trends that exist in this species.

This is where our research comes in. Compared to the amount of research carried out in breeding populations of Golden-winged Warblers, relatively little has been done to link breeding populations to nonbreeding sites and identify migration routes in geographically isolated populations of Golden-winged Warblers. We developed a study to attach the smallest geolocators available (at the time in 2013 this was just under 0.50 g) to 9-10 g Golden-winged Warblers at multiple sites throughout their breeding distribution where they were experiencing variable population trends. Our main goal was simply to find out where these different populations went after they left the breeding grounds in North America and determine if the populations overlapped or occurred together in Central and South America during the nonbreeding period. If the declining Appalachian populations spent the winter in a region that was isolated from the stable western Great Lakes population, it is logical that the breeding-grounds population trends we observe might be caused at least in part by nonbreeding factors.

After all the hard work of redesigning the marking methods, getting the geolocators deployed, stressing over whether it would work, and then retrieving the geolocators, it was exciting to analyze the data and see entire year-long tracks of individual Golden-winged Warblers and to think about the distances these birds traveled and the places they spent their time when away from our study sites. We found that Golden-winged Warblers from Appalachian breeding populations spent the nonbreeding period in South America, mostly in a relatively small region on the border of Columbia and Venezuela. In contrast, Golden-winged Warblers from the western Great Lakes breeding population occurred throughout northern Central America in countries like Honduras, Nicaragua, Guatemala, Belize, and Mexico.

In the end, this geolocator study demonstrates a clear difference in nonbreeding locations and migration strategies among these different populations of Golden-winged Warblers. These differences are urgently meaningful from a conservation and management standpoint as they highlight a potential cause for regional differences in population trends observed across the breeding distribution. If nonbreeding factors are limiting Golden-winged Warbler population growth in the Appalachians, perhaps the most important implication of our work is to provide information that might help conservationists revise and refocus current strategies to better and target declining populations that spend the nonbreeding period in northern Colombia and Venezuela.

Read more at henrystreby.com.

Combined Count Data Reveals Shifts in Hawks’ Migratory Behavior

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Red-tailed Hawks’ migratory behavior appears to be changing. Photo credit: N. Paprocki, HawkWatch International

Bird species’ distributions and migratory behavior are shifting in response to changes in climate and land-use, but surveys that focus on a particular season can cause scientists to miss trends in the bigger picture. A new study from The Condor: Ornithological Applications tackles this problem by combining Red-tailed Hawk counts from both migration and winter, and finds that while the hawks’ numbers are stable overall, their migratory behavior is undergoing a change.

To get a more complete picture of Red-tailed Hawks’ population status, Neil Paprocki of HawkWatch International and his colleagues compared data from the Raptor Population Index, which is based on counts of raptors during migration, with Christmas Bird Counts, which are carried out by amateur birdwatchers in December and January. They found declining hawk numbers at 43% of the migration count sites, with increases at only a few sites located in the western flyway. Among the winter counts, however, 67% showed increases, spread across all regions surveyed. The greatest increases were reported from northern latitudes.

The migration data alone would suggest that Red-tailed Hawks are on the decline in North America—but the full picture actually indicates stable to increasing populations, with an ongoing shift in migratory behavior. The hawks appear to be wintering farther north than they have in the past, explaining the lower numbers seen on migration. “We wanted to develop a more comprehensive view of raptor population change, using data from multiple stages of the annual cycle,” says Paprocki. “What does this study tell us about how Red-tailed Hawks are adapting to environmental change? It doesn’t tell us anything directly, but the results suggest that Red-tailed Hawks may be responding to climate change, land use change, or other environmental changes by migrating shorter distances or becoming year-round residents.”

Hawks breed at low densities, including at high latitudes where they can be difficult to survey.   This makes migration and winter surveys especially important for monitoring these species. “Many North American hawks, eagles, and falcons are counted at watch sites during migration, and monitoring programs use counts as an index of population size. The interpretation that trends or lack thereof in count data are indicative of changes in populations assumes that the proportion of the population passing by the migration site remains consistent over time. Unfortunately, this assumption may be at risk, as there is strong evidence that raptor migration strategies are changing in response to climate and land use change,” according to Julie Heath of Boise State University, a raptor biologist who was not involved with the study. “Paprocki et al. do an excellent job highlighting how changes in annual cycles could affect our ability to monitor raptors and how the use of additional information can provide insight to trends in migration counts.”

Combining migration and wintering counts to enhance understanding of population change in a generalist raptor species, the North American Red-tailed Hawk is available at http://americanornithologypubs.org/doi/full/10.1650/CONDOR-16-132.1.

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.

Allen’s Hummingbird Boom Missed by Breeding Bird Surveys

During courtship displays, this species produces sound using its tail feathers

Migratory and nonmigratory Allen’s Hummingbirds appear to be on different population trajectories. Photo credit: A. Varma/varmaphoto.com

Allen’s Hummingbird has been placed on several conservation watchlists, as breeding bird surveys indicating population declines have spurred concerns that climate change may push it out of Southern California. However, local birdwatchers have reported at the same time that the non-migratory subspecies of Allen’s Hummingbird, once restricted to the Channel Islands, is now a common sight at feeders in Riverside and Los Angeles. Why the discrepancy? A new commentary published in The Condor: Ornithological Applications may provide answers.

The University of California–Riverside’s Chris Clark used data from eBird, an online platform where citizen scientist birdwatchers can submit their sightings, to reexamine Allen’s Hummingbird population trends in urban Southern California since 1990. He found a steep increase in the species’ prevalence in eBird checklists from the region, with Allen’s Hummingbirds reported in 20% of all checklists submitted from Southern California today. Because the pattern is consistent year-round, it cannot be driven by the migratory subspecies, which is only in the area for part of the year.

While it appears that urban landscaping has created new habitat and food supplies that are exploited year round by non-migratory Allen’s Hummingbirds, ecological differences between the two subspecies could also be helping to drive their different trajectories. “The non-migratory Allen’s Hummingbird seems to do better in parks and backyards than does the migratory subspecies,” says Clark. “It also produces more offspring during the breeding season. Either of these reasons might be why the non-migratory subspecies seems to be doing so well within urban areas of the greater L.A. area.”

“This commentary is an object lesson in the importance of considering all sources of data and all aspects of a species’ natural history when its range and trends are modeled. As Clark emphasizes, the accuracy of such models matters when they are the basis for setting conservation priorities,” according to Philip Unitt of the San Diego Natural History Museum. “The paper calls attention to the continuing dramatic increase in the range and numbers of Allen’s Hummingbird, bringing into contact two subspecies differing in multiple aspects of their biology, an opportunity for study of evolution in process.”

eBird records show substantial growth of the Allen’s Hummingbird (Selasphorus sasin sedentarius) population in urban Southern California is available at http://americanornithologypubs.org/doi/abs/10.1650/CONDOR-16-153.1.

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.

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Greater Sage-Grouse More Mobile Than Previously Suspected

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Greater Sage-Grouse occasionally make long-distance movements between leks. Photo credit: J. Carlson

Greater Sage-Grouse are thought to return to the same breeding ground, or “lek,” every spring—but how do populations avoid becoming isolated and inbred? A new study from The Condor: Ornithological Applications used thousands of DNA samples collected at leks across four states to reveal that some sage-grouse travel more widely than anyone suspected and, in doing so, may temper inbreeding and isolation.

Using genetic markers in DNA extracted from feather and blood samples, Todd Cross of the U.S. Forest Service Rocky Mountain Research Station and his colleagues identified more than three thousand individual sage-grouse that visited leks across the northeastern portion of the birds’ range over seven years. Approximately two and one-half percent of birds in the sample turned up twice, a mixture of individuals returning to the same lek in different years, visiting different leks within one year, or visiting different leks in different years. Seven birds made movements of over 50 kilometers (over 30 miles), six of which occurred within a single breeding season.

The study used 7,629 samples collected from 835 leks in Idaho, Montana, and North and South Dakota between 2007 and 2013. While the results support the idea that most grouse are faithful to their chosen lek sites, some individuals clearly make long-distance movements, which could help prevent inbreeding within leks and expand the size of the genetic neighborhood. “Our research demonstrates that Greater Sage-Grouse are an even more mobile species than we had realized before, moving large distances of up to 194 kilometers—over 120 miles—in a single breeding season,” says Cross. “These findings highlight the importance of landscape-scale efforts that conserve movement corridors.”

“The use of genetic recapture information opens an exciting new door to understanding the landscape dynamics of the Greater Sage-Grouse,” according to Pat Deibert, National Sage-Grouse Conservation Coordinator for the U.S. Fish and Wildlife Service. “Species conservation is more than tracking the number of individuals: We also have to understand how a species uses the landscape and the associated impacts on their vital rates. The data presented in this paper provide additional insight to effective landscape management and conservation design for the Greater Sage-Grouse and will contribute to the continual improvement of management for this species.”

Genetic recapture identifies long-distance breeding dispersal in Greater Sage-Grouse (Centrocercus urophasianus) is available at http://americanornithologypubs.org/doi/abs/10.1650/CONDOR-16-178.1.

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.

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Swamphens Signal Dominance Through Fleshy Faces

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Pūkeko’s facial shields convey their social status. Image credit: C. O’Connor

What’s in a face? In addition to their plumage, Pūkeko—large purple swamphens found in New Zealand—convey information about their status through their faces. A new study from The Auk: Ornithological Advances shows that the strongest predictor of male dominance in Pūkeko is the size of their frontal shield, a fleshy ornament on their bill that can change quickly.

Cody Dey of McMaster University (now at the Great Lakes Institute for Environmental Research) and his colleagues measured the plumage coloration and frontal shield width and coloration of 272 adult Pūkeko on New Zealand’s North Island, then tested how those traits were related to the dominance hierarchies they observed within groups. While shield color and plumage brightness and color were all related to social dominance, the strongest predictor was frontal shield width. Frontal shield width was also strongly correlated with testes mass, suggesting that it is the primary status signal for males.

Pūkeko shields can decrease in size in as little as a week in response to aggressive challenges from other males, thanks to hormonal changes. “The take-home message from this study is that birds use both feather coloration and bare-part coloration as signals, but these different types of signals have different properties, and bare-part signals in particular are probably more accurate because they can be updated,” says Dey. “Feather-based signals can only change when the individual molts, which usually only happens once or twice a year. Since we have mostly been studying feather coloration in birds, we might have been missing a great deal of information about the role of avian coloration.”

“This exciting study on the understudied Pūkeko adds strong support to our growing understanding of bare part signaling. In particular, the authors reveal the dynamic nature of pigmented bare in communicating status and condition information,” adds Franklin and Marshall College’s Daniel Ardia, an expert on signaling in birds who was not involved with the study. “The differences they find between frontal shield signaling and plumage reveal the complexity of signaling and demonstrates that bare parts are not simply redundant signals.”

A bare-part ornament is a stronger predictor of dominance than plumage ornamentation in the cooperatively breeding Australian Swamphen is available at http://americanornithologypubs.org/doi/full/10.1642/AUK-16-119.1.

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.