THE EFFECT OF SUPPLEMENTAL FOOD ON TIME BUDGET AND BODY CONDITION IN THE BLACK-REDSTART PHOENICURUS-OCHRUROS

We studied the effect of supplementary food on time allocation, breedi ng success and parental body condition in Black Redstarts Phoenicurus ochruros in the Alps, NW Italy. Time budgets of both males and females were significantly affected: individuals provided with supplementary food spent less time foraging and more time preening and vigilant. In accordance with predictions on the difference between sexes in parenta l investment, males increased the time spent singing by 5 to 26% and r educed the number of feeds to nestlings from 5.4 to 2.0 h(-1). Females showed a higher rate of nestling feeding which offset reduced provisi oning of nestlings by the males. The breeding success of control and s upplemented pairs was similar. The mass of adults was monitored using electronic balances placed near the nest cavity. Control pairs decreas ed in mass while adults given supplementary food showed an increase. T he difference between control and fed adults was greater in males than females. The hypothesis of an adaptive reduction in mass by all indiv iduals due to programmed anorexia is not supported. We discuss the alt ernative hypothesis of a cost of reproduction utilizing estimates of e nergy expenditure from time budgets.