Food handling time of Blue Tit chicks:: constraints and adaptation to different prey types

Extensive literature shows that lepidopteran larvae constitute the most important component of the diet of nestling tits (Parus spp.). In Blue Tits Parus caeruleus, breeding is usually timed to match the nestling stage to the period when caterpillars are most abundant. This is true even in places where caterpillars are not very numerous and many alternative prey types have to be used. in a study of a Corsican Blue Tit P. c. ogliastrae population, characterised by the extensive use of non-caterpillar prey, we compared some aspects of the behaviour of nestlings when fed caterpillars, grasshoppers and spiders. The expectation deduced from ecological and behavioural literature that nestlings should be best able to swallow caterpillars was confirmed. Chick prey handling time could be ranked from caterpillars (the shortest time), through spiders to grasshoppers (the longest time). Handling time increased exponentially with prey size within each prey category and was to some extent subject to variation between broods. Consequently, the behaviour of nestlings provides new support for the idea that Blue Tits are best adapted to eating caterpillars and that mechanical constraints prevent them from using very big prey items, especially non-caterpillar prey, and that this is likely to affect their choice of prey. Such constraints may be less strict in Great Tits Parus major because of their larger body size.