Effects of male removal on reproductive success and provisioning in the Eurasian Treecreeper (Certhia familiaris)

Abstract

In biparental bird species the optimal level of parental care of one member of the pair gen- erally depends on its mate's strategy. In monogamy, a predicted response to reduced pa- rental care by one parent is incomplete compensation by its partner. The importance of male parental care has been suggested to vary also according to environmental conditions during breeding. From our previous studies, double-brooded male Eurasian Treecreepers (Certhia familiaris) were found to desert their nests more often during second broods, when food conditions were generally good. Here, we studied the importance of male pa- rental care in this species, by testing the effects of male removal on the parental behavior and reproductive success during the first broods, when food is scarcer. The aim was to de- termine the degree to which female parents could increase their workload to compensate for the male absence. We did this by measuring feeding rate, and the size and composition of food loads of widowed and paired females. Food abundance was measured within Treecreeper territories, immediately after fledging, as a measure of territory quality rela- tive to the breeding success of both paired and widowed females. Our results showed that widowed females increased their feeding rate enough to compensate for the loss of their mate. However, widowed females produced fewer young, which were also of lower nest- ling weight, than control pairs. The success of the second brood, in the same breeding sea- son, was also lower among widowed females with new males than among the control fe- males, despite all experimental females having the opportunity to re-nest.