Seasonal variation in breeding performance and nestling diet of Cirl BuntingsEmberiza cirlusin England

Abstract

The survival rates and outcomes of Cirl Bunting nests were recorded over a four-year period. Significant annual variations in nest survival were found at both the egg and the young stage. Significant seasonal variations in survival rates were found, with late nests being over twice as likely to produce fledglings as early ones. Most losses occurred at the chick stage early in the season and were due to predation and starvation. Chicks in poor condition through food shortage may have been more likely to be predated as a result of increased begging activity. Late season chicks had a very different diet to those hatched early in the season, being fed a much higher proportion of Orthoptera. They also enjoyed higher growth rates and survival. Rainfall had a small detrimental effect on growth rates, probably as a result of insect prey becoming hard to find. Loss of arthropods due to intensification of livestock farming and loss of diversity in the agricultural landscape may have contributed to the decline of the species in the UK.