Under-Studied Boreal Habitat Key for North America’s Ducks

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Researchers used ducks harvested by hunters to learn new details about waterfowl migration. Photo credit: M. Carriere

Knowing where migrating birds came from and where they’re headed is essential for their conservation and management. For ducks, most of this information comes from long-term bird-banding programs, but this type of research has limits—despite all the birds harvested by hunters, only a small percentage of banded birds are ever recovered. A new study from The Condor: Ornithological Applications takes on the challenge of gaining information from unbanded birds by using stable isotope ratios, which reflect where birds were living while growing their feathers. These results reveal that the northern reaches of Canada may have underappreciated importance for North America’s waterfowl.

Canada’s Saskatchewan River Delta is North America’s largest inland delta and is a key stopover site for migrating ducks. To learn more about the origins of ducks using delta habitat, Christian Asante of the University of Saskatchewan, Keith Hobson of the University of Western Ontario, and their colleagues analyzed the isotopes in feather samples from 236 ducks from five species, all harvested by hunters in the region during migration in 2013 and 2014. Hydrogen and sulfur isotope ratios give scientists different information—hydrogen isotope ratios vary predictably with latitude, while sulfur isotope ratios reflect the type of food a bird eats and underlying geology—but together they indicated that as many as half the ducks using the delta during migration originated in the vast and nearly inaccessible areas of boreal forest and wetlands to the north.

The research required close collaboration with the area’s hunters. “Working on this project was a great experience,” says local community member Michela Carriere, who was hired to do the field work for the study. “I spent a few weeks collecting samples from the ducks and getting to know the hunters and the guides. Twice a day a load of ducks would come in and I would collect samples and label and package them, plucking feathers and extracting tissues. The hardest part was the labeling, which has to be done meticulously. I would spend hours each day collecting and organizing the samples.”

The results show that the boreal habitat’s contribution to North America’s waterfowl populations, though poorly documented, may be crucial. This region faces increasing threats from climate change and other factors, and isotopic monitoring offers a new means of tracking the effects on birds. “Our study is important for two reasons,” says Hobson. “First, it demonstrates clearly that the delta is a major fall refueling station for birds breeding in the north. Second, it shows once again how origins and regions of productivity can be determined using the simple isotope approach with feathers from hunter-killed birds. This major potential tool in waterfowl management has been largely overlooked in North America for too long.”

Tracing origins of waterfowl using the Saskatchewan River Delta: Incorporating stable isotope approaches in continent-wide waterfowl management and conservation is available at http://americanornithologypubs.org/doi/abs/10.1650/CONDOR-16-179.1.

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.

AUTHOR BLOG: Tracking Semipalmated Sandpiper Migration

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Photo credit: B. Winn

Stephen Brown

Linked paper: Migratory connectivity of Semipalmated Sandpipers and implications for conservation by S. Brown, C. Gratto-Trevor, R. Porter, E.L. Weiser, D. Mizrahi, R. Bentzen, M. Boldenow, R. Clay, S. Freeman, M.-A. Giroux, E. Kwon, D.B. Lank, N. Lecomte, J. Liebezeit, V. Loverti, J. Rausch, B.K. Sandercock, S. Schulte, P. Smith, A. Taylor, B. Winn, S. Yezerinac, and R.B. Lanctot, The Condor: Ornithological Applications 119:2, May 2017.

The Semipalmated Sandpiper (Calidris pusilla) is a small shorebird, most commonly seen on migration along the coastlines of the eastern United States. It is historically one of the most widespread and numerous shorebird species in the Western Hemisphere, breeding across the North American Arctic tundra, but major population declines have been documented in the core of the nonbreeding range in northern South America. Breeding populations have also declined in the eastern North American Arctic, but appear to be stable or increasing in the central and western Arctic. To help understand what is causing the declines and work toward conservation of this species, we set out to track migration routes and stopover sites using light-level geolocators, a relatively new technology which determines the bird’s position on earth by measuring the length and timing of daylight throughout the year. The major challenge to using these tags is that you have to catch the bird once to put on the geolocator and then again the next year to retrieve it, which requires finding the same bird again in the vast arctic tundra. Luckily, they tend to return to the same breeding areas the next year.

Our large group of 18 partner organizations worked collaboratively to carry out the study across the entire North American Arctic from Nome, Alaska, to Hudson Bay, and we attached 250 geolocators to birds by mounting expeditions to 8 different field sites. Our field crews faced challenging conditions, working in the Arctic where the weather is always unpredictable and where both grizzly bears and polar bears regularly visit field sites. We repeated expeditions the next year to each site, and recovered 59 of the units by recapturing birds. The treasure trove of data showed migration routes and stopover sites from the entire year in the life of each bird, and showed that birds breeding in the eastern Arctic wintered in northeastern South America. Birds from eastern Alaska and far western Canada wintered from Venezuela to French Guiana. Central Alaskan breeders wintered across a very wide range from Ecuador to French Guiana. Birds that bred in western Alaska wintered mainly on the west coasts of Central America and northwestern South America, outside the nonbreeding region in which population declines have been observed.

Our results confirm that Semipalmated Sandpipers that breed in the eastern Arctic and use the Atlantic Flyway also use the areas in South America where population declines have been detected, suggesting that declines may be concentrated in populations along the Atlantic Flyway and in the eastern Arctic. However, because some birds from sites as far west as Barrow, Alaska, also used the areas in northeastern South America where declines have occurred, further work is needed to localize the geographic areas used by declining populations, and therefore the potential causes for the declines. We identified several new stopover and wintering areas, where implementing conservation actions to preserve the habitats used by Semipalmated Sandpipers could contribute to protecting the species. We measured a larger impact of geolocators on return rates than has been observed for larger shorebirds, indicating that caution should be used when working with small shorebirds, and that potential new information gains from additional geolocator studies should be weighed against expected impacts on individual survival. Our data also provided new insights about how long birds stay at migration stopover sites, which will be useful to studies that measure and monitor the total size of populations using these sites. Understanding the connections between breeding, migration, and wintering areas for these populations of a widespread yet declining shorebird can help future studies identify the causes of declines and ensure the effectiveness of targeted conservation efforts.

Sandpiper Detectives Pinpoint Trouble Spots in Continent-Wide Migration

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A Semipalmated Sandpiper wearing a geolocator. Photo credit: B. Winn

Understanding and managing migratory animal populations requires knowing what’s going on with them during all stages of their annual cycle—and how those stages affect each other. The annual cycle can be especially difficult to study for species that breed in the Arctic and winter in South America. A new study from The Condor: Ornithological Applications tackles this problem for Semipalmated Sandpipers, historically one of the most widespread and numerous shorebird species of the Western Hemisphere, whose populations in some areas have undergone mysterious declines in recent years.

Stephen Brown, Vice President of Shorebird Conservation for Manomet, assembled a large group of partner organizations to deploy 250 geolocators, tiny devices that use light levels to determine birds’ locations, on adult sandpipers at sites across their breeding range in the North American Arctic. Recapturing 59 of the birds after a year to download their data, they found that the eastern and western breeding populations use separate wintering areas and migration routes. Birds that breed in the eastern Arctic overwinter in areas of South America where large declines have been observed. The researchers believe these declines are tied to hunting on the wintering grounds and habitat alteration at migration stopover sites, although their precise impacts remain unclear.

“This study was a response to the discovery of a large decline in the population of Semipalmated Sandpipers in the core of their wintering area in South America, and the need to determine which birds were involved. We didn’t know if the decline affected the entire population or just part of it,” says Brown. “Bringing together the 18 partner organizations that worked collaboratively on this project allowed us to track the migration pathways used by Semipalmated Sandpipers at the enormous geographical scale of their entire North American Arctic breeding range and provided critical new information about what sites are important to protect to support their recovery.”

“The authors here present one of the few studies that examine year-round connectivity, including stopover sites, of Arctic-breeding shorebirds,” according to the University of Guelph’s Ryan Norris, an expert on migration tracking who was not involved with the study. “Multi-site, range-wide studies on connectivity, such as this, are critical if we are to understand the population consequences of environmental change in migratory birds.”

Migratory connectivity of Semipalmated Sandpipers and implications for conservation is available at http://americanornithologypubs.org/doi/full/10.1650/CONDOR-16-55.1.

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.

About Manomet: Manomet is a nonprofit organization that believes people can live and work today in ways that will enable our world to thrive and prosper tomorrow. Manomet’s mission: applying science and engaging people to sustain our world. Visit www.manomet.org for more information.

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How Reliable Are Traditional Wildlife Surveys?

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A Sandhill Crane from the Rocky Mountain population. Photo credit: T. Cacek

To effectively manage a wildlife species, one of the most basic things you need to know is how many of them are out there. However, it’s almost never feasible to count every single individual—so how do the results of wildlife surveys compare to true population size? A new study in The Condor: Ornithological Applications tests this using the results of more than thirty years of surveys of the Rocky Mountain population of Sandhill Cranes.

A three-year “moving average” is often used to smooth out year-to-year irregularities in survey results, but this approach has never been evaluated. Brian Gerber of Colorado State University and William Kendall of the U. S. Geological Survey assessed whether the annual population changes reported by these moving averages were realistic, based on what is known about crane demographics, and how they compared to the results of a more sophisticated statistical approach called a hierarchical Bayesian time series model. They found that while the moving average population estimates were reasonable, the more complex method performed better over a large number of scenarios.

Bayesian approaches offer a structured way to incorporate new information as it becomes available. “The model-based approach we looked at is very flexible and has some major advantages over other methods,” says Gerber. “By taking a Bayesian approach, we can include additional information about both the observation process and the true population to obtain more realistic estimates and predictions. Also, the model-based approach includes measures of uncertainty about our population estimates, which are not usually provided by more common approaches and are crucial for understanding the level of confidence we have about our estimates.”

Evidence suggests that management practices over the last twenty years have largely met the annual population objectives for the Rocky Mountain Sandhill Crane population. “Looking forward,” adds Gerber, “managers may still be interested in adopting our more robust modeling approach due to its flexible framework, which makes implementing any changes relevant to the survey easier.” The investment in collecting these long-term data may pay off not just for crane management, but for an advance in methods that can be applied to other species as well.

Evaluating and improving count-based population inference: A case study from 31 years of monitoring Sandhill Cranes is available at http://americanornithologypubs.org/doi/full/10.1650/CONDOR-16-137.1.

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.

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.