Nestlings reared by males are in better body condition than those reared by females in uniparental European Penduline Tits

Abstract

Conditions encountered during early development affect future survival and reproduction in many bird species. For parents, it is important what body condition the nestlings will achieve at fledging because the condition affects the offspring’s chances to survive and reproduce in the future. However, there is a trade-off between the number of nestlings and their condition. We studied parental behaviour and nestling body condition in uniparental Penduline Tits. In this small passerine, the parental care (incubation and food provisioning) is provided by the female only (49% of clutches in the study population) or the male only (15%). In addition, over a third of clutches are deserted by both parents before the start of incubation. We found that female-only cared clutches had more eggs and nestlings and produced more fledglings than male-only cared clutches. The incubation behaviour and incubation temperature in both types of clutches were similar. The provisioning rate per brood was positively, and the provisioning rate per nestling was negatively, correlated with brood size. Although males cared for smaller clutches, parent sex was not significant in both models of provisioning rates (per brood and per nestling). Moreover, the provisioning rate did not predict the brood’s average nestling condition. However, nestlings reared in broods with male care were in better condition than those reared by females. At the age of 13 days, they had a higher scaled mass index (describes the relative size of energy reserves) and higher haemoglobin levels. The results suggest that the lower productivity of male-only cared clutches, compared to those cared for only by females, may be compensated by the higher condition of nestlings. Information about the recruitment success of broods cared for by males and females will be necessary to test this prediction.