Food
|
Reproductive success (number
of young produced per pair per year) in relation to the availability
of caterpillars (mg per 100 leaves) on the main study plot at
Hubbard Brook from 1986 to 1998 (food data were not available for
1999; data from Holmes, Rodenhouse, and Sillett). |
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.