Combined analysis of roadside and off-road breeding bird survey data to assess population change in Alaska
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Full Publication: https://doi.org/10.1650/CONDOR-17-67.1Product Type: Journal Article
Year: 2017
Authors: Handel, C. M. and J. R. Sauer
Suggested Citation:
Handel, C. M. and J. R. Sauer. 2017. Combined analysis of roadside and off-road breeding bird survey data to assess population change in Alaska. The Condor 119(3):557-575. doi:10.1650/CONDOR-17-67.1
Abstract
Management interest in North American birds has increasingly focused on species that breed in Alaska, USA, and Canada, where habitats are changing rapidly in response to climatic and anthropogenic factors. We used a series of hierarchical models to estimate rates of population change in 2 forested Bird Conservation Regions (BCRs) in Alaska based on data from the roadside North American Breeding Bird Survey (BBS) and the Alaska Landbird Monitoring Survey, which samples off-road areas on public resource lands. We estimated long-term (1993–2015) population trends for 84 bird species from the BBS and short-term (2003–2015) trends for 31 species from both surveys. Among the 84 species with long-term estimates, 11 had positive trends and 17 had negative trends in 1 or both BCRs; negative trends were primarily found among aerial insectivores and wetland-associated species, confirming range-wide negative continental trends for many of these birds. Three species with negative trends in the contiguous United States and southern Canada had positive trends in Alaska, suggesting different population dynamics at the northern edges of their ranges. Regional population trends within Alaska differed for several species, particularly those represented by different subspecies in the 2 BCRs, which are separated by rugged, glaciated mountain ranges. Analysis of the roadside and off-road data in a joint hierarchical model with shared parameters resulted in improved precision of trend estimates and suggested a roadside-related difference in underlying population trends for several species, particularly within the Northwestern Interior Forest BCR. The combined analysis highlights the importance of considering population structure, physiographic barriers, and spatial heterogeneity in habitat change when assessing patterns of population change across a landscape as broad as Alaska. Combined analysis of roadside and off-road survey data in a hierarchical framework may be particularly useful for evaluating patterns of population change in relatively undeveloped regions with sparse roadside BBS coverage.
Keywords: Breeding Bird Survey, population trends, shorebirds, passerines, hierarchical model
Annotation
Alaska not only serves as the terminus for multiple migratory pathways from North and South America, but also supports avian populations migrating north from nonbreeding areas in Oceania, Australasia, Antarctica, and Africa. During the past half-century, the highest rates of climatic warming in North America have occurred in Alaska and northwestern Canada and the resulting physical and biotic changes are altering the distribution and composition of vegetation and ecosystem processes across the landscape. Changes in climate can affect habitat and bird populations, and may potentially make them more vulnerable to effects of development and other anthropogenic activities.