MALE PARENTAL CARE PROMOTES EARLY FLEDGING IN AN OPEN-NESTER, THE WILLOW WARBLER PHYLLOSCOPUS-TROCHILUS

The importance of male parental care to female reproductive success wa s investigated in the monogamous Willow Warbler Phylloscopus trochilus by removing the male parent at two different stages of the breeding c ycle. Females that were widowed at the start of egg-laying continued b reeding and managed to raise their brood on their own with no apparent reductions in numbers fledged or fledgling body-mass, The widowed fem ales compensated for the loss of male assistance by increasing their o wn food provisioning rate as compared with control females, However, w idows spent less time brooding the small young, and the growth rate of nestlings was reduced, In nests where the male parent was removed 7 d ays after the eggs hatched, the subsequent growth rate of nestlings wa s still affected, which suggests that male care is influential through out the nestling period. On average, broods reared by widows fledged 2 days later than did broods of control females. An extension of the ne stling period may appreciably affect reproductive success, since 68% o f nests failed due to predation, mostly during the nestling period, We suggest that the main role of male parental care in the Willow Warble r is to assure a high growth rate of nestlings, which leads to early f ledging and hence a reduced risk of nest predation.