Reproductive success (number of young produced per pair per year) in relation to the abundance of chipmunks and red squirrels (number detected per survey hour) on the main study plot at Hubbard Brook from 1988 to 1999 (predator data were not available for 1986, 1987, and 1991; data from Holmes, Rodenhouse, and Sillett).

Squirrels and chipmunks are the major predators of Black-throated Blue Warbler eggs and nestlings. When researchers looked at the relationship between the numbers of these mammals and the warblers’ reproductive success in different years, they found that the birds had lower success in years when these predators were more common.

In this figure, each year is plotted as a point, and the line shows the average effect of predator abundance on nest success.


Learning module developed by K. Langin, H. Sofaer and S. Sillett for the Hubbard Brook Research Foundation (2009).