Yearling Recruitment

The number of yearlings - or first time breeders - on the 64 ha study plot at Hubbard Brook in relation to the reproductive success of warbler pairs the previous year (yearling data were not available for 1999; data from Holmes, Rodenhouse, and Sillett).

So far we've shown that predators, food and density are all factors that influence the reproductive success of Black-throated Blue Warblers at Hubbard Brook. But does that really make a difference to the total population size? Researchers testing this question found out that it does. Reproductive success during the breeding season in one year determines the number of yearlings – or first time parents - on the study plot the following year. This indicates that factors during the breeding season, particularly those that lower reproductive success, play an important role in determining the size of the warbler population.

Of course, environmental factors during the migratory and wintering periods are also important (in fact, they play a huge role in limiting survival of adults). However, this research does emphasize that changes in the environment affect the reproductive success and population size of Black-throated Blue Warblers.