January 26, 2011
The range limits for different bird species are often changing, and recently many wintering birds have been shifting northward. The question is whether these range shifts are due to milder winter temperatures, or to an increase in bird feeding, which would allow species to survive in conditions that would normally be too harsh. Researchers from Project FeederWatch recently analyzed observations submitted by participants during the 2007-2008 season, focusing on eighteen common feeder species and incorporating information about urbanization, temperature, and precipitation for each count site.
It turns out that climate plays a critical role in shaping the range limits for many common feeder birds. Despite the presence of feeders throughout their range, several species did not persist throughout the winter in colder environments. Weather also played a role, however, and many species were more likely to visit feeders more often during harsh weather conditions such as cold snaps.
Different species are also affected differently by factors such as urbanization. Some species are less likely to be found in urbanized areas, such as the Downy Woodpecker. Because these species are not adapted to urban environments, birds in more urbanized areas have a lower ability to tolerate very cold temperatures.
Other species, such as the House Sparrow, demonstrate better adaptation to urban environments. For these species, urban areas act as refuges, allowing birds to tolerate colder temperatures.
Check out the Project FeederWatch Map Room to see how the ranges for different species of feeder birds fluctuate over the years.
Source: Zuckerberg B., D. N. Bonter, W. M. Hochachka, W. D. Koenig, A. T. DeGaetano, and J. L. Dickinson. 2010. Climatic constraints on wintering bird distributions are modified by urbanization and weather. Journal of Animal Ecology.