The influence of climate on avian nest construction across large geographical gradients

Aim: Nest microclimate is a critical determinant of the survival and development of embryonic and juvenile birds. While abiotic variables such as temperature, precipitation and elevation will influence the conditions experienced by offspring within the nest, parent birds may also exercise some control through nest design and the selection of construction material. The aim of this study is to determine whether avian nest construction and the composition of nest construction material is influenced by geographical variation in climate. In addition, this study aims to address whether the correlation between nest construction and elevation highlighted by other studies is independent of the association between elevation and climate, or if other unmeasured variables are at play. Location: Australia Methods: We measured the structural and thermal properties of 201 cup-shaped nests, from 36 Australian passerine species, and related these to temperature, precipitation and elevation. Results: The rate of heat loss from avian nests is correlated with temperature, precipitation and elevation. Birds that construct nests in cool climates use well-insulating materials irrespective of precipitation, while birds in warm climates use poorly insulating materials when exposed to high rainfall but not when exposed to low rainfall. Main conclusions: Local climate influences the construction of nests, through modification of the materials used, and therefore the rate of heat loss from the nest as a whole. In many climates, birds use well-insulating materials; however, birds breeding in warm and wet climates construct their nests with materials that have a higher thermal conductivity. Such nests are possibly less absorptive and able to dry out faster following a rain event, to restore the insulating function of the nest. These findings highlight the importance of studies over large geographical scales for understanding nest construction by birds.