Breeding Slows Down for the Caterpillars
Abstract from Journal of Animal Ecology
17th April 1996
Another report of research work on Great Tits at Wytham Woods (Oxford, England) is included in the Journal of Animal Ecology (64: 451-458).
Arie van Nordwijk, Robin McCleery and Chris Perrins used up to 39 years of data to investigate the selection of timing of breeding in relation to caterpillar growth and temperature.
The selection for early laying in the Great Tit was very strong, to try to get their brood correlated with the caterpillars. There is a problem for the tits since caterpillars develop into ideal chick food much faster in warm weather and slower in cold. This is happening while the Great Tits are incubating and during the first week the chicks are in the nest.
It is very hard for the Great Tits to speed up their breeding but they can (and do) slow it down if the caterpillars are slowed down by cold temperatures. It is important that they do so since the chances of their chicks surviving to recruit to the breeding population the next year is very strongly determined by the availability of good numbers of the right sized caterpillars while they are in the nest.