Paternal care in Pied Flycatchers Ficedula hypoleuca: Energy expenditure in relation to plumage colour and mating status

Females may benefit from expending more resources in care of offspring sired by sexually attractive males than by those of unattractive males in species with biparental care. Attractive males may therefore reduce their share of parental expenditure to increase own survivorship and to further mating success. On the other hand, if direct benefits through male care are important for female mate choice, sexually attractive males may be expected to have a higher parental expenditure than unattractive males. We measured daily energy expenditure of attractive and unattractive (i.e. brightly and dull coloured) male Pied Flycatchers Ficedula hypoleuca during a period of intensive parental care applying the doubly-labelled water technique. We did not find any consistent differences in energy expenditure between bright and dull males, lending little direct support to either hypotheses. Combined with previous studies of the same species, we suggest that bright males are more efficient in bringing food to the brood per unit of energy spent. Polygamously mated males divide their feeding effort among the primary and secondary brood(s), although most care is given to the primary brood. We found that bigamous males had higher daily energy expenditures than monogamous males. This result suggests that polygamy is associated with energetic costs to males, possibly related to the need of travel between nests but perhaps also to an overall higher parental investment. We argue that costs to males should be incorporated in discussions on the evolution of polygamy.