ESTUARINE WINTER FEEDING PATTERNS OF LITTLE GREBES TACHYBAPTUS-RUFICOLLIS IN CENTRAL WALES

The feeding ecology of wintering Little Grebes was studied on a bracki sh tidal river in central West Wales during the winters of 1981/2-1983 /4. Peak numbers occurred in late November and mid-February. Increased wind strength reduced the likelihood of birds being present in the st udy area. The frequency of their occurrence was highest at low and hig h tide, when flood conditions made shallow water (< 2 m) available for feeding. Little Grebes foraged for 85-89% of daylight hours, and evid ence is provided to suggest that feeding only occurs during the day at this site. Inter-dive recovery time increased exponentially with dive duration, suggesting increased energetic costs of prolonged dives. Di ve time increased with water depth, hence feeding at greater depths is probably disproportionately more costly than in shallow water. Since feeding success (based on prey handling on the water surface) also dec lined with depth of the water column, it would appear that the observe d patterns of use of shallow water in time and space are related to th e energetic costs and benefits of foraging in different water depths.