Effect of Weather Conditions on Dynamics of the Black-headed Gull, Chroicocephalus ridibundus, Wintering on Jakusevec, Zagreb City Rubbish Dump

Temperature and precipitation are known to have an effect on the onset of bird migration, but studies were mostly taken on Passeriformes. Between 2001 and 2006 we studied the wintering numbers and dynamics of migration of a short-distance migrant, black-headed gull, Chroicocephalus ridibundus, on Zagreb city rubbish dump, Jakusevec. Mean monthly numbers showed significant negative correlation with the local winter temperature, with higher numbers in the coldest months. Arrival of black-headed gulls correlated with North Atlantic Oscillation (NAO) index for the period from September to November. Precipitation didn't have an effect on the timing of migration or maximum numbers. Our results indicate that arrival time for black-headed gull depended on the conditions in breeding areas, while departure time did not respond to NAO or local temperature.