Blue tit Cyanistes caeruleus males increase their reproductive effort when subject to a flea experimental manipulation

Abstract

Parasites exert a strong selection pressure on their hosts as manifested in behavioural antiparasite traits to reduce negative impacts on fitness. The numerous nest‐dwelling ecto‐parasites residing in avian nests make altricial birds excellent model‐systems for investigating the relationship between parasites and their hosts. Here, we experimentally increased natural levels of hen fleas Ceratophyllus gallinae in blue tit Cyanistes caeruleus nests during incubation, and tested their effects on parental incubation behaviours and reproductive performance. Our experimental addition of fleas resulted in an increase in feeding effort of males to incubating females. Frequency of male feedings was also positively related to clutch size. These results suggest that males increase their reproductive effort in flea manipulated and large broods. This will, at least partly, compensate female costs in nests with high ecto‐parasite density and many nestlings. Furthermore, nestling mass at day six in experimental nests decreased with brood size, which was not the case in nests with a natural level of fleas. In line with male incubation feeding, parents may try to compensate for the costs inflicted by the fleas but can only partly compensate when brood size is large.