PARENT SESSION
Contributed Oral Session 18: Avian Communities and Populations
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 524 C, Level 5, Palais des congrès de Montréal
Changes in bird migration times in eastern North America.
Miller-Rushing, Abraham*,1, Lloyd-Evans, Trevor2, Primack, Richard1, 1 Boston University, Boston, MA2 Manomet Center for Conservation Sciences, Manomet, MA
ABSTRACT- Several studies have demonstrated that birds are migrating to their breeding grounds earlier in recent (warm) years than they did in past (cool) years. These studies have generated intriguing questions related to trends toward earlier migration time. We used 33 years of bird capture data from Manomet, Massachusetts to address some of these questions for 32 species of North American passerines. First, we sought to determine if changes in first arrival dates--the unit of observation used in most studies of bird migration times--accurately reflected changes in populations' mean arrival dates. We found that the first birds of each species arrived 0.20 days later each decade. In contrast, the average birds of each species arrived 0.78 days earlier each decade. The difference in the two trends was largely explained by declining population sizes, a factor ignored in most previous studies. Second, we examined the power of local temperatures along the migration route and climate modes (e.g., North Atlantic Oscillation) to explain changes in migration times. We found that each species tends to rely on just one climate variable, but that species vary in the climate variable on which they rely. Finally, we examined factors that might cause species to respond to global warming at different rates. Among the factors we examined, only migration distance seemed to explain any of the differences in migratory responses to global warming. The shorter the species' migration route, the more responsive was that species' migration time to warming, on average. Our findings suggest that the migration times of many bird species may be responding to warming significantly faster than previously thought. Our findings also set groundwork for making predictions on how migratory bird communities might change as species migration times change at different rates.
Key words: global warming, birds, migration, phenology