Avian Conservation and Ecology (Dec 2022)
The Great Lakes shape nocturnal bird migration in southern Ontario
Abstract
Coastlines in marine areas are known to influence use of the airspace as a habitat by migrating birds, but less is known about how the complex configuration of the Great Lakes influences bird migration patterns. If birds alter their migration in response to the lakes, they may become concentrated in specific areas, which should receive particular attention from a conservation perspective. In this study, we examined the effects of these lakes on flight directions and densities of nocturnally migrating birds in southern Ontario, Canada, using data from two Canadian weather surveillance radars for three years in autumn (2009–2011) and two years in spring (2010–2011). On nights of high migration intensity, we estimated migration directions and bird densities 2.5 and 6 hours after sunset, using a sampling design that tested specific hypotheses about the lake effects at different scales. We found that the Great Lakes influenced migration patterns, with many birds flying along a NE–SW corridor, in autumn passing between Georgian Bay and Lake Ontario and then likely crossing Lake Erie. In spring, most birds passed over the eastern half of Lake Erie and then flew northeast between Georgian Bay and Lake Ontario. These concentration areas had estimated densities of migrating birds up to 4 times those in other areas. Although some birds flew across the middle of the lakes, many birds appeared to follow routes that minimize the flight distance over water. This was particularly evident later in the night when migration directions shifted even more to avoid crossing lakes. These concentration areas include some of the most heavily developed lands in southern Ontario. To obtain better spatiotemporal information that can be used to guide conservation in this region, we recommend further analyses of radar data at a finer scale and over a longer time interval using refined algorithms.
