Abstract

Bird nests are variable in design but all are constructed for the purpose of incubation. The potentially onerous energetic costs of incubation have meant that previous studies have focussed on thermal insulation but nests are often exposed to a variety of environmental factors, including rainfall. Those few studies that have investigated the
effects of water on nests have saturated the walls by soaking but this may not reflect what a nest would typically
encounter in situ during rainfall. Here, nests of four species of songbird (Common Chaffinch Fringilla coelebs, Common
Linnets Linaria cannabina, Meadow Pipits Anthus pratensis, and Whinchats Saxicola rubetra) were investigated using temperature
loggers to determine the effect of simulated rainfall on nest wall insulation. Simulated rainfall, produced by
water dripping through a coffee percolator, significantly reduced the insulatory values of nests, and significantly
increased the rate of cooling of temperature loggers inside the nest cup. No significant effect of species, or nest mass,
was observed. Even when wet nest walls provided some insulation but whether this is attributable to the nest materials
chosen by each species was not clear. The nest site chosen by the birds may also offer considerable protection from
the weather. Further research is needed to better understand how rainfall affects the insulative properties of nests in
situ.