The trade-off between molt and parental care in Hooded Warblers: Simultaneous rectrix molt and uniparental desertion of late-season young.

Abstract

Temporal overlap between parental care and molt occurs frequently in birds, but few studies have examined how individuals manage conflicts between these 2 demanding phases of the annual cycle. The potential for trade-offs between molt and parental care is especially high in the Hooded Warbler (Setophaga citrina) because (1) all rectrices are replaced simultaneously during primary molt, leaving birds temporarily without a functional tail; and (2) the tail plays an important role in foraging, as birds use their white tail spots and tail-flicking behavior to startle insect prey. I examined how simultaneous rectrix molt affected late-season parental care in a color-banded population of Hooded Warblers in northwest Pennsylvania, USA. Of 62 adults initiating rectrix molt before the end of parental care, 43 (69%) deserted their late-season nestlings and fledglings, leaving the mate to provide all remaining parental care. Because females initiate rectrix molt significantly later than males, most instances of uniparental desertion involved molting males abandoning fledglings or nestlings, but rare cases of postfledging desertion by females also occurred. Although most molting parents deserted, the probability of desertion decreased significantly with brood age, presumably because the costs of providing parental care during molt decline as fledglings approach independence. The probability of desertion by the male also decreased significantly with male age, suggesting that more experienced males can successfully balance the dual demands of molt and late-season parental care. In females, however, the only instances of desertion involved unusually old females ≥5 yr old, which suggests that rare cases of female desertion may occur as a mechanism to reduce reproductive effort late in life. My findings indicate that conflicts between parental care and molt, and the strategies that individuals use to manage those conflicts, merit increased attention from ornithologists seeking to understand the full annual cycle of migratory songbirds.