Effects of Year and Box Size on Construction of Eurasian Nuthatch Sitta europaea Nests

Studying nest construction provides insight into the functional and ecological aspects of this key behaviour of avian reproductive biology. Studies have shown that passerines construct nests out of a range of different materials, but the number of species represented in the literature remains low. This study examined nests constructed by the Eurasian Nuthatch Sitta europaea in nestboxes at various sites in North West England over the period 2011–2020. Nests were collected and weighed after breeding to quantify the materials used by the birds in order to determine whether there were any differences in nest construction behaviour among years. The study also allowed for the comparison of nests built in standard and large nestboxes. Nuthatches used mud to plaster the inside and outside of the nestbox; however, they relied heavily on bark flakes (84% of nest mass), but also included wood chips and leaves to construct the nest. Bark pieces were taken from Common Hazel Corylus avellana, Yew Taxus baccata or Scots Pine Pinus sylvestris, depending on availability in the immediate area around the nestbox, although Hazel bark was the preferred material. There was little effect of sample year on nest composition except for an increase in wood chips over the sample period. Thermal and hydrological properties of the bark flakes did not depend on the tree species. Nuthatches nesting in large nestboxes produced heavier nests, but this did not affect their reproductive success, which implies that the energy required for nest construction does not necessarily impose such an excessive burden on breeding birds that it adversely affects their fitness.