Breeding large gulls in Poland: distribution, numbers, trends and hybridisation (2006)

Neubauer, G., M. Zagalska-Neubauer, R. Gwiazda, M. Faber, D. Bukaciński, J. Betleja & P. Chylarecki, 2006.
Breeding large gulls in Poland: distribution, numbers, trends and hybridisation.
Vogelwelt, 127 : 11–22.

The current situation of three species of large gulls (L. argentatus, L. cachinnans and L. michahellis) in Poland is presented based on results of own studies and published data. Herring Gulls started to breed in the country in the late 1960s and rapidly increased in numbers until the early 1990s. This exponentially increasing population trend, coupled with southward expansion and colonisation of inland areas of N Poland has been recently reverted, with the population estimated at 1,200–1,500 pairs in the early 2000s, down from some 1,900–2,100 a decade ago. The increase of Caspian Gull in southern Poland is exponential and very fast with an annual growth rate of 33% between 1997 and 2004; the population reached 480 pairs in 2004. The Yellow-legged Gull remains a rare breeder and its population probably does not exceed 5–10 pairs. Hybridisation occurs mainly between the commonest species, Herring Gull and Caspian Gull, and is caused primarily by an apparently random pairing in mixed colonies in central Poland. The high frequency of mixed pairs (c. 60% and c. 40% respectively) and a high share of hybrids were recorded at two sites in the Vistula river valley: the middle Vistula and the Włocławek Reservoir. The situation of particular breeding colonies in southern and central Poland seems to be unstable, which favours the exchange of individuals between these breeding places. Frequent dispersal along a north-south axis also favours hybridisation.

Key words: Herring Gull Larus argentatus, Caspian Gull Larus cachinnans, range expansion, colonisation, hybridisation, Pologne.