Reproductive Success

Reproductive success (number of young produced per pair per year) on the main study plot at Hubbard Brook from 1986 to 1999 (data from Holmes, Rodenhouse, and Sillett).

So what did the researchers find? Well, first of all they found that the average pair of warblers was able to raise just over 3 offspring over the course of a typical breeding season. The average level of reproductive success varied widely between years, however. In some years more than 4 offspring were produced, and in other years reproductive success was as low as 2 offspring per pair.

Researchers then wanted to know why reproductive success, the number of young raised per pair, varied so much between years. Was it nest predation? Differences in food availability? Was it density? Fortunately, the long-term data that have been collected on all of those variables gave the researchers an opportunity to answer that question. And as it turns out, all three - predation, food, and density - play an important role in limiting the reproductive success of Black-throated Blue Warblers at Hubbard Brook.