Mate and nestling desertion in colonial little egrets

I observed 25 Little Egret (Egretta garzetta) nests during the nestling period. Eleven (44%) were deserted by the female parent, one (4%) by the male, and three (12%) by both parents. Deserters of both sexes left nests soon after single parent care became feasible ([x bar] = 22 +/- 4 days after hatching, ca. 40% of the time from hatching to the independence of young). Small broods were deserted significantly more frequently than large ones. No chicks died after uniparental desertion. Deserters reacquired courtship coloration on their lores and repeatedly visited particular sites away from their nests before desertion, which suggests that they paired with new mates before leaving their primary nests. During biparental care periods, I found no sexual difference in feeding frequency, though males attended their young longer than females in the daytime. The tendency for female egrets to become ready to remate earlier than males may be because they invest less prezygotic effort in second breeding attempts than males. Males have to establish new territories and guard their new mates against extrapair copulations, although male-biased operational sex ratio also might favor female desertion. Received 22 September 1988, accepted 16 December 1988.

Masahiro Fujioka, Auk: Vol. 106, No. 2, April-June, 1989