Results from a second herring gull (Larus argentatus) cull on the island of Scharnhörn, Elbe estuary

Published source details von Prater J. & Vauk G. (1988) Ergebnisse einer zweiten Silbermöwen (Larus argentatus) Bestandsregelung auf der insel Scharhörn, Elbmündung. Zeitschrift für Jagdwissenschaft, 34, 120-124.
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Summary

Scharnhörn island is an important breeding sites for terns Sterna spp. on the German North Sea coast. Through the 1980s, the island experienced a dramatic increase in the herring gull Larus argentatus population (1980-1985: 107% increase per year). As a consequence, more and more tern breeding habitat was occupied by gulls. In order to reduce the resultant negative effect on breeding tern populations, culls of gulls were undertaken in 1986 and 1987. The paper summarised here gives a background to the consequences of these culls.

On Scharnhörn, culls took place in spring 1986 (168 herring gulls), and in spring (27-30 May) 1987 (137 herring gulls and six lesser black-backed gulls Larus fuscus killed).

Gulls were shot by trained marksmen from two camouflage hides positioned within the breeding colony. Carcasses were collected and removed; sex and age was determined. The number of breeding pairs of herring gulls and of the four nesting tern species was estimated.

The cull in 1986 reduced herring gull numbers by 75% (i.e. from an estimated 500 to 125 breeding pairs). Subsequently, there was a marked increase in breeding sandwich terns Sterna sandvicensis (42% increase to 2,530 pairs); estimates also pointed to an increase in common S.hirundo and arctic tern S.paradisea pairs, but there was no change in the continuing decline of little tern S.albifrons. The authors attribute the increases of the three larger Sterna spp. to the reduction of breeding gulls.

In 1987, of the estimated 125 gull clutches prior to culling, 86 were still being incubated in the following week despite at least 78 breeding females being killed; the authors speculate that some of the remaining partners of a former pair continued incubating (it is known that herring gulls do this but are rarely successful). In mid-June, an additional 39 gull nests were found; some were newly constructed and some contained freshly laid eggs. Thus the breeding population of herring gulls remained about the same as the pre-cull level. This 'within season' recovery is thought part due to immigration of gulls from neighbouring islands.

Of the recovered carcasses, the sex ratio was: herring gulls (129 individuals), 78 male: 51 female (60.5% : 39.5%); lesser black-backed gulls (five individuals): 4 male: 1 female. Among the males, seven (9%) had remnants of immature plumage (all herring gulls), among the females, three had immature plumage remnants (one herring gull; two lesser black-backed gulls); this suggests that almost all birds were potentially breeding at the site.

Note: If using or referring to this published study, please quote the original paper. This German language paper, translated and summarised for Conservation Evidence, has an English and French abstract, and is available at:

http://www.springerlink.com/contant/p75176q451q4160m/fulltext.pdf