Individual study: Effects of culling breeding lesser black-backed gulls Larus fuscus and herring gulls Larus argentatus at the Abbeystead and Mallowdale gullery, Lancashire, England
Wanless S. & Langslow D.R. (1983) The effects of culling on the Abbeystead and Mallowdale gullery. Bird Study, 30, 17-23
Although only established in 1938, by the 1970s a gull colony known as the Abbeystead and Mallowdale gullery (54º01'N, 2º35'W), in the Forest of Bowland, Lancashire, had become the largest inland concentration of gulls Larus spp. in Britain. However, following the detection of unacceptably high levels of potentially dangerous bacteria in a nearby stream used for human water supply, approval was granted for large-scale cull of gulls. This study investigated the effects of repeated culls of lesser black-backed gulls Larus fuscus and herring gulls Larus argentatus on the size and extent of this moorland breeding colony.
Breeding gulls were culled by placing stupefying baits in nests from 17 May-7 June 1978, 21 May-7 June 1979, 19-22 May and 16-19 June 1980, and 17-19 May and 7-9 June 1982. Attempts were also made to minimise gull breeding output by destroying nest contents. Although there was no official cull in 1981, c. 2,000 gulls were shot that year.
The colony was surveyed during the first three weeks of May in 1979-1982. As it was not feasible to conduct a complete census, sample counts were made in quadrats. The number and size of quadrats varied from year-to-year, but the area sampled was between 183,000 and 325,000 m² (or roughly 3-5% of the total colony area).
The number of gulls recovered dead after culling was 21,258 in 1978, 12,573 in 1979, 6,338 in 1980 and 5,397 in 1982. Allowing for an estimated 10% more gulls dying unrecorded, the proportion of the breeding population killed each year was estimated to be 47% in 1978, 27% in 1979 and 31% in both 1980 and 1982. The proportion of birds recruited to the breeding population each year was very variable, with substantially more birds than expected recruited in certain years. Nevertheless, between 1978 and 1982, the estimated breeding population fell from 49,480 to 18,960 individuals. Although the extent of the main colony remained largely unchanged (at c.6 km²) throughout the study period, the average density of nests decreased from 0.42 per 100 m² in 1979 to 0.16 per 100 m² in 1982.
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