Antal og overnatningspladser for Stormmåger og Hættemåger i Danmark i julen 2010 og 2011

摘要

Danmark er sammen med den vestlige del af Østersøen et kerneområde for fældende og overvintrende Stormmåger Larus canus og Hættemåger Chroicocephalus ridibundus (Meltofte & Faldborg 1987, Laursen et al. 1997), men der er aldrig foretaget nogen koordineret optælling af disse fugle, idet de findes stort set overalt og derfor er vanskelige at dække. Men udenfor yngletiden optræder en stor andel af dem koncentreret på kollektive overnatningspladser, hvor de er forholdsvis lette at tælle. På den baggrund blev alle feltornitologer gennem DOF's caretakernetværk, Netfugl og bladet Fugle i Felten opfordret til at tælle de to arter på deres overnatningspladser indenfor dagene 24. december - 2. januar både i 2010/11 og 2011 /12. Julen blev valgt, fordi de fleste ornitologer har fri og kan besøge sådanne lokaliteter sidst på eftermiddagen, hvor fuglene samles og stadig kan tælles.%During the Christmas and New Year holidays 2010/11, the Danish Ornithological Society organized a census to improve our knowledge on the numbers and use of communal night-time roosts of wintering Common and Black-headed Gulls in Denmark. As early as Christmas, the winter had become severe with extensive ice cover on lakes and fjords, and therefore the census was repeated the following year, when the winter was mild. The totals of individuals recorded appear in Tab. 1 and the distributions of birds at night roosts and daytime occurrences are shown on the maps in Fig. 2 and 3. More than 7 1/2 and 2 1/2 times as many Common Gulls and Black-headed Gulls, respectively, were recorded in the mild winter 2011/12 compared to the severe winter the year before (Tab. 1). 30% of Common Gulls and 46% of Black-headed Gulls were recorded on communal night-time roosts in 2010/11, while the corresponding ratios for 2011/12 were 74% of Common Gulls and 56% of Black-headed Gulls(cf. Tab. 1). Due to uncertainty about the geographical coverage of the census, I dare not estimate the totals of the two species of gull wintering in Denmark, but rough estimates suggest that at least 10% and 2%, respectively, of the European mid-winter populations of Common and Black-headed Gulls are present in Denmark in mild winters. According to the 1%-criterion, at least six sites qualify as sites of international importance for Common Gulls, while no sites qualify for Black-headed Gulls.