G. Bjornstad et Jt. Lifjeld, MALE PARENTAL CARE PROMOTES EARLY FLEDGING IN AN OPEN-NESTER, THE WILLOW WARBLER PHYLLOSCOPUS-TROCHILUS, Ibis, 138(2), 1996, pp. 229-235
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.