Relationship Between Spatial Distribution Of Breeding Divers And The Availability Of Fishing Waters

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Abstract
The spatial distribution of both black-throated [Gavia arctica] and red-throated divers [G. stellata] varies considerably in Scotland. Both species nest very close to the edge of an inland water; but there is no direct relationship between the availability of freshwater and the density of breeding pairs. Both species fish in the same waters, and although they exhibit different preferences for nesting, they compete for food. Calculations were made of the available water area per pair within a radius of 8 km from the center of each study area; over 95% of all fishing was done within 8 km of the nest. When the total water area was considered, there was still a wide variation in apparent requirements per pair; but when shallow water alone was considered, then in 6 areas out of 9 the water area required for fishing was close to 2 km2 per pair. The mean of the 9 areas was 2.5 km2/pair. Possible reasons for divergences from this figure are suggested. The spatial distribution of divers in Scotland is determined by the availability of shallow water suited to their normal fish prey, with about 2 km2 per pair being the requirement.

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