Parental feeding in the Red‐throated Diver Gavia stellata

Abstract

We describe parental feeding by Red‐throated Divers Gavia stellata from 14.2–44.7 h of observation on each of eight pairs, coordinated with simultaneous observations at potential fishing lakes, in southwest Sweden. All pairs bred on small tarns (0.8–10 ha), normally devoid offish, and foraged in larger freshwater lakes 1.9–7.7 km away from the breeding site. Most pairs directed the majority of the foraging trips to the same lake. On average, parents made seven foraging trips per day per young. Both parents contributed to feeding activities and, in broods of two young, each chick obtained an equal amount of food. Cyprinid fish (mainly Rutilus rutilus) and salmonids (mainly Coregonus albula) dominated. Qualitative predictions from central‐place foraging theory concerning relationships between the time for a foraging trip and the size of prey delivered by a single‐prey loader were not corroborated. The amounts of fish biomass delivered were in agreement with or lower than predictions from models on daily energy requirements; this result is related to the decreased abundance of fish in acidified freshwater lakes and the decline of Red‐throated Diver populations in south Sweden.