As researchers predicted, in years when caterpillars were more numerous, the birds were able to raise more young. How did this work? It turns out that it’s not because nestlings starve in years with fewer caterpillars, but instead birds adjust the number of nests they build to the food availability. In really good years, birds even start over once their nestlings have left the nest! So it’s possible to raise two groups of nestlings in a single breeding season, but the number of birds that try to do this is greater when there is more food.
|Learning module developed by K. Langin, H. Sofaer and S. Sillett for the Hubbard Brook Research Foundation (2009).|