Determinants of the re‐occupation and size of Grey HeronArdea cinereabreeding colonies in northern Poland

Abstract

Birds select habitats on the basis of structural characteristics, food and nest-site availability or other features that affect survival and reproduction. This study investigates factors influencing colony re-occupation, the number of nests in 2013 and changes in the numbers of nest between 2004 and 2013 in re-occupied colonies of Grey Herons Ardea cinerea in northern Poland. The effects of following features around every colony were analysed: area of hydrographic and habitat features, habitat patchiness and microscale features. Among 28 colonies occupied in 2004, 43 % were re-occupied in 2013. Logistic regression models revealed that models with greater area of the sea coastline zone and lower area of the water body shoreline zone and also small number of pastures determined the best colony reoccupation. Only models with an area of water bodies and a number of pastures were significant, suggesting the important influence of other non-habitat factors on colony re-occupation. Ordinary least square (OLS) regression analysis revealed that in re-occupied colonies the number of nests in 2013 was higher in heronries with greater area of sea coastline zone, smaller number of forest patches and shorter distance to the nearest road. OLS regression analysis revealed that the number of nests increased between 2004 and 2013 in the colonies with greater areas covered by forests, greater number of water bodies, shorter distance to the rivers and longer distance to the sea. Our study revealed the importance of wetland habitat features to colony re-occupation, its size and changes in size.