Behavioural response of female dark-eyed juncos to the experimental removal of their mates: implications for the evolution of male parental care

Abstract

Male dark-eyed juncos, Junco hyemalis, are monogamous and normally help females feed nestlings. We removed males at hatching of their eggs and examined female parental behaviour in response to male removal. We compared parental behaviour of unaided females (experimentals) with that of (1) females aided by their mates (control females) and (2) females and their mates working together (control pairs). Unaided females fed their young at least twice as often as did aided females and as often as the combined efforts of pairs. The increased rate of food delivery by unaided females was accompanied by a decrease in time brooding the young and an increase in the amount of time the female's nest was unattended, suggesting that feeding and brooding are competing parental behaviours. Feeding rates of both unaided females and pairs increased as brood size increased, but the response to brood size was stronger in unaided females than in either aided females or pairs. An earlier study indicated that, despite their compensatory feeding rates, unaided females experienced greater partial brood loss than did pairs. Perhaps males bring more food per feeding trip, or food of a different quality. It seems likely that males can improve fledging success by bringing food to the young, both during the early nestling stage when brooding is crucial and also later, during the period of rapid growth.