NOCTURNAL FEEDING BY DARK-BELLIED BRANT GEESE BRANTA-BERNICLA-BERNICLA

The occurrence and extent of nighttime feeding by Dark-bellied Brent G eese Branta bernicla bernicla on salt marshes adjacent to their tidal roost site were assessed on the north Norfolk coast using position-sen sitive radio transmitters. Nine birds were monitored on 143 bird-night s, and feeding was recorded on 87, The frequency of feeding by night v aried widely between individuals. The mean proportion of the night spe nt feeding for one bird was 19.7 +/- 8%, Of this, 59% occurred within +/- 1.5 h of high tide, Neither the proportion of the whole night spen t feeding nor the intensity of feeding around high tide varied with th e length of the night or with time after sunset at which high tide occ urred, The extent of nocturnal feeding was also independent of the bri ghtness and duration of moonlight, The birds fed for significantly lon ger on colder nights, and there was a significant positive relationshi p between the proportion of the night spent feeding and maximum temper ature the preceding day. Analysis of daytime activity budgets on inlan d pastures showed that the proportion of time engaged in nonfeeding, e nergy-expensive activities was also positively related to maximum dayt ime temperature, Increases in the proportion of the night spent feedin g after warmer days were achieved by increasing the period of time spe nt feeding on either side of the high tide, not by increasing feeding intensity at high tide, It is concluded that the geese compensate for increased energy expenditure during the day by increasing the extent t o which they feed at night. Implications of increasing energy expendit ure as a result of disturbance during the day are discussed.