Unequal sex ratios and their consequences in Herring Gulls (Larus argentatus)
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Animal ecology
Herring gull
SUMMARY This paper presents evidence for the involvement of herring gulls ( Larus argentatus ) as vectors in the recent outbreaks of Salmonella montevideo in sheep and cattle in Scotland and suggests that the transfer can take place over considerable distances. The breeding area in Scotland of herring gulls which overwinter in N.E. England is remarkably similar to the geographical distribution of the outbreaks. This pattern, together with the feeding behaviour of herring gulls on farmland, the presence of S. montevideo in herring gulls just before their departure from the wintering area and the timing of the return just before the peak of outbreaks are all circumstantial evidence implicating this gull in the outbreaks. The rapid return of these gulls to their breeding areas means that S. montevideo can be transported long distances in one day and raises the possibility that the original source of S. montevideo could have been in N. E. England rather than in Scotland.
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The Herring Gull Larus argentatus is considered a regular but scarce visitor to Spain, but its detailed status is uncertain. Here I present a compilation of published (primarily annual bird reports) and unpublished information (internet forums, direct communications by local ornithologists, ringing recoveries) to clarify the distribution and numbers of Herring Gulls in Spain, and their origins. More detailed information on age composition and phenology is presented for Asturias (NW Spain), perhaps the region where the species is most studied. According to ring recoveries (n = 43), the majority of Herring Gulls visiting Spain belong to the subspecies L. a. argenteus (mainly from the British Isles), with only 7% coming from breeding areas of the Nordic subspecies L. a. argentatus. Most observations occur in autumn and winter, being scarcer in spring and summer, and numbers vary between years. Two-thirds of birds recorded were in their first two years of life, with adults comprising only a quarter of the total. Ringing recoveries suggest Herring Gulls were more common in Spain 30+ years ago than at present. Data from winter censuses in Asturias between 2002 and 2007 gave a mean proportion of 1.06% Herring Gulls amongst the Yellow-legged Gull L. michahellis contingent. It is estimated that between 250 and 400 Herring Gulls are present in Asturias in mid January, and between 500 and 700 in the whole of Spain at the time of the winter censuses. There are two possible but unconfirmed attempts of breeding.
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Archipelago
Charadriiformes
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Two Herring Gulls with yellow legs were observed on 21 March 1983 at Isahaya, Kyushu, Japan. A field description based on a comparison with Larus argentatus vegae, which were also present, leads to the conclusion that they were L. a. mongolicus a sub-species not previously recorded in Japan.
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