Energetic Bottle-Necks During Breeding and the Reproductive Cost of Being Too Early

Experimental provision of extra food before egg-laying resulted in blue tit females starting to breed significantly earlier than unmanipulated females. When the females had laid their first egg, the experimental food source was withdrawn and females were thus manipulated to lay, incubate and feed nestlings at lower food levels than unmanipulated females. Although tricked into breeding earlier, the experimental females laid the same number of eggs, had no more laying gaps and produced eggs of equal size as the unmanipulated females. Females manipulated to start breeding early started to incubate significantly later in relation to clutch completion than did controls