Abstract
We examined the influence of both season and hydrographic and meteorological factors on seabird abundance in the southern North Sea. Seabirds were counted from ships in a study area of 27.8 x 32.8 km on 407 d from 1990 to 2007. Two hydrographic and 5 meteorological parameters were taken from archived data. The relationships between bird abundance and abiotic parameters were investigated by generalised additive models for 3 distinct seasons. The species in the study area exhibited different seasonal patterns. While some species were present year-round, others occurred only at certain periods. Despite these substantial changes in abundances, the nature of the interactions between bird abundances and abiotic parameters did not vary much between seasons. All 5 meteorological and 2 hydrographic parameters significantly influenced the abundance of seabird species, though to a different degree. The single factors that most often had a significant influence in the single models were wind field, sea surface temperature anomaly, sea surface salinity anomaly and air pressure change. The quantitative composition of the seabird community differed significantly between onshore wind and offshore wind conditions. It is assumed that hydrographic parameters are relevant for the birds by determining their foraging habitats and that atmospheric parameters influence flight conditions during foraging and migration.