Incubation feeding as a male tactic for early hatching

Abstract:
Male marsh tits, Parus palustris, regularly feed their mates from the beginning of nest building until hatching. Over three periods (the 15 days preceding egg formation, egg formation/laying and incubation) the number of food passes by the male to the female increased significantly. There was a significant negative relationship between the frequency with which the male fed the female in the nest during incubation and the length of the incubation period. Female blue tits, Parus caeruleus, experimentally supplied with food in the nestbox during incubation had a significantly shorter incubation period than control females. Clutches of experimentally fed females also tended to hatch more successfully. It is concluded that feeding of the female by the male is a nutritional contribution and that the shorter incubation period and increased hatching success enhance the fitness of both parents. However, the male should balance the benefits against the costs in time and energy and therefore not necessarily work at a maximal level. In accordance with this is the finding that the male's provisioning rate increased when ambient temperatures decreased. Adverse weather may jeopardize the whole or large proportions of the clutch, thereby significantly reducing the benefit from the current breeding attempt.