First‐egg date and air temperature affect nest construction in Blue TitsCyanistes caeruleus, but not in Great TitsParus major

Capsule For nest construction by Blue Tits, but not Great Tits, first-egg date (FED) and air temperature significantly affected the mass of the nest as a whole and some of its component parts. To test the hypothesis that use of nest materials is influenced by prevailing climatic conditions during nest construction. Nests used in the study were built by Blue Tits Cyanistes caeruleus and Great Tits Parus major in nestboxes at a site in Lincolnshire, England during the 2008 and 2009 breeding seasons. Nests were dissected into their component parts and then weighed. Stepwise discriminant analysis showed that the asses of grasses, feathers and bark were significantly affected by species (all higher in Blue Tits) and year significantly affected the mass of wool and dust in the nests. ANOVA showed that total mass of the nest was not significantly affected by year of construction or species. By contrast, species, but not year, did significantly influence the masses of animal- and plant-derived materials in the nest. In Blue Tit nests there were significant correlations between FED and the mass of animal-derived material in 2008, but with plant-derived material in 2009. There were significant correlations between mean air temperature recorded during the seven days up to FED the mass of the nests and their plant-derived materials. No significant correlations were observed FED and nest components for Great Tits. Nest construction is potentially affected by a variety of environmental factors, which may impact upon how nests function. A better understanding of how nest variability affects its function may allow better assessment of how climate change may impact upon the reproductive performance of birds