Vermont Project: Identifying Important Stopover Locations for Migrating Birds

Vermont Project

Identifying Important Stopover Locations for Migrating Birds

January 1999 - January 2003

Personnel

Participating Agencies

The Nature Conservancy
U.S. Geological Survey

During migration, landbirds often concentrate near geographical barriers and along river valleys. However, the relative importance of various areas and habitat types to migratory landbirds remains unknown. Identifying migration stopover concentration areas is the fist step toward integrating migration habitat priorities into avian conservation plans. A new remote sensing technology, NEXRAD WSR88-D radar, allows us to identify stopover concentration areas and rank the relative importance of various areas.

Research Publications

Research Publications	Publication Date
Bonter, D. N., T. M. Donovan, and E. W. Brooks. 2007. Daily changes in energetic condition in landbirds during migration stopover on the south shore of Lake Ontario. Auk 124:122-133 \| Abstract \| Download	January 2007	Assigning conservation priorities to areas used by birds during migration requires information on the relative quality of areas and habitats. The rate at which migratory birds replenish energy reserves during stopover may be used as an indicator of stopover-site quality. We estimated the rate of mass gain of 34 landbird species during stopover at a near-shore terrestrial site on the south shore of Lake Ontario in New York during 12 migration seasons from 1999 to 2004. The average rate of mass gain was estimated by relating a measure of condition to time of capture (hour after sunrise) with linear regression. Data from 25,385 captures were analyzed. Significantly positive rates of mass change were detected for 20 of 30 species during spring migration and 19 of 21 species during autumn migration. No significantly negative trends were detected in either season. Daily rates of mass gain across all species averaged 9.84% of average lean body weight during spring migration and 9.77% during autumn migration. Our regression estimates were significantly greater than estimates from traditional analyses that examine mass changes in recaptured birds. Analyses of mass changes in recaptured birds revealed a mean daily change of -0.68% of average lean mass in spring and 0.13% in autumn. Because of sampling biases inherent in recapture analyses, the regression approach is likely more accurate when the assumptions of the method are met. Similar studies in various habitats, landscapes, and regions are required to prioritize conservation efforts targeting migratory stages of the annual cycle.
Bonter, D. N., T. M. Donovan, E. Brooks. 2008. What are we missing with ground-level mist nets? Using elevated nets at a migration stopover site. Journal of Field Ornithology 79:314-320. \| Abstract \| Download \| Publisher Website	September 2008	Mist nets deployed in a standard ground-level fashion capture birds approximately 0.5–2.6 m above the ground. In habitats where the vegetation extends above this height, standard mist net deployment may inadequately sample the targeted avian community and age- and sex-classes within species. Such sampling biases may raise questions regarding studies based on data from mist-net captures. To determine if birds were equally likely to be captured by mist nets at different heights, we constructed a series of paired ground-level and elevated mist nets (hereafter "net rigs") at a research station in western New York State. Net rigs were operated during 14 migration seasons from 2000 to 2006 (spring and fall each year), and 19,735 birds of 118 species were captured. Capture rates were significantly higher in ground-level nets, but 12 species were only captured in elevated nets. Of 44 species with at least 50 captures, 25 species were more likely to be captured in the ground-level nets and two species in the elevated nets. For four of 18 species, more birds were captured in the elevated nets during fall migration than during spring migration. We conclude that standard ground-level net placement was more efficient in capturing birds in the secondary growth habitats that we sampled. However, ground-level nets may not adequately sample the entire targeted community or all age- or sex-classes within species.
Bonter, D. N., S. A. Gauthreaux, Jr., and T. M. Donovan. 2009. Characteristics of important stopover locations for migrating birds: Remote sensing with radar in the Great Lakes Basin. Conservation Biology 23:440-448. \| Abstract \| Download	April 2009	A preliminary stage in developing comprehensive conservation plans involves identifying areas used by the organisms of interest. The areas used by migratory land birds during temporal breaks in migration (stopover periods) have received relatively little research and conservation attention. Methodologies for identifying stopover sites across large geographic areas have been, until recently, unavailable. Advances in weather-radar technology now allow for evaluation of bird migration patterns at large spatial scales. We analyzed radar data (WSR-88D) recorded during spring migration in 2000 and 2001 at 6 sites in the Great Lakes basin (U.S.A.). Our goal was to link areas of high migrant activity with the land-cover types and landscape contexts corresponding to those areas. To characterize the landscapes surrounding stopover locations, we integrated radar and land-cover data within a geographic information system. We compared landscape metrics within 5 km of areas that consistently hosted large numbers of migrants with landscapes surrounding randomly selected areas that were used by relatively few birds during migration. Concentration areas were characterized by 1.2 times more forest cover and 9.3 times more water cover than areas with little migrant activity. We detected a strong negative relationship between activity of migratory birds and agricultural land uses. Examination of individual migration events confirmed the importance of fragments of forested habitat in highly altered landscapes and highlighted large concentrations of birds departing from near-shore terrestrial areas in the Great Lakes basin. We conclude that conservation efforts can be more effectively targeted through intensive analysis of radar imagery.

Cooperative Fish and Wildlife Research Units Program: Vermont Education, Research and Technical Assistance for Managing Our Natural Resources

Vermont Project

Identifying Important Stopover Locations for Migrating Birds

January 1999 - January 2003

Personnel

Participating Agencies

Cooperative Fish and Wildlife Research Units Program: Vermont
Education, Research and Technical Assistance for Managing Our Natural Resources