Prey selectivity and parental feeding rates of Blue Tits Cyanistes caeruleus in relation to nestling age

Abstract

Capsule The effect of nestling age (7, 10 and 13 days old) on prey choice by Blue Tits Cyanistes caeruleus seems to be related to time constraints on food selectivity rather than chick gape-size limitations. Aims To study age differences in the nestling diet of Blue Tits and how the relative contribution of each parent varies as the nestlings grow older. Methods The provisioning activity of Blue Tit parents was recorded using infrared video cameras when chicks were 7, 10 and 13 days old. Results Nestling age had no influence on the percentage of folivorous caterpillars in the diet of nestlings. Male and female parents changed their provisioning strategy with nestling age; this change was similar in adults of both sexes. Blue Tit nestlings received a smaller proportion of spiders and a greater proportion of Tortricid larvae (small, low-mobility caterpillars) as they grew older. At the age of seven days, females brought a lower proportion of Noctuids (large caterpillars) to the nest than their mates. The role of each parent in provisioning young varied with nestling age. Males fed their young at a lower rate when they were seven days old compared with later in the nestling period, whereas females tended to invest more in provisioning effort early in the nestling period in comparison with subsequent age-classes. Conclusion Contrary to what would be expected based on the gape-size constraint hypothesis, the youngest nestlings (seven days old) were fed with a higher proportion of large caterpillars (Tortricidae). Our results suggest that at these ages nestling gape-size does not restrict parents’ prey-choice strategies.