title: Adaptive latitudinal variation in Common Blackbird Turdus merula nest characteristics.
abstract: Nest construction is taxonomically widespread, yet our understanding of adaptive intraspecific variation in nest design remains poor. Nest characteristics are expected to vary adaptively in response to predictable variation in spring temperatures over large spatial scales, yet such variation in nest design remains largely overlooked, particularly amongst open-cup-nesting birds. Here, we systematically examined the effects of latitudinal variation in spring temperatures and precipitation on the morphology, volume, composition, and insulatory properties of open-cup-nesting Common Blackbirds' Turdus merula nests to test the hypothesis that birds living in cooler environments at more northerly latitudes would build better insulated nests than conspecifics living in warmer environments at more southerly latitudes. As spring temperatures increased with decreasing latitude, the external diameter of nests decreased. However, as nest wall thickness also decreased, there was no variation in the diameter of the internal nest cups. Only the mass of dry grasses within nests decreased with warmer temperatures at lower latitudes. The insulatory properties of nests declined with warmer temperatures at lower latitudes and nests containing greater amounts of dry grasses had higher insulatory properties. The insulatory properties of nests decreased with warmer temperatures at lower latitudes, via changes in morphology (wall thickness) and composition (dry grasses). Meanwhile, spring precipitation did not vary with latitude, and none of the nest characteristics varied with spring precipitation. This suggests that Common Blackbirds nesting at higher latitudes were building nests with thicker walls in order to counteract the cooler temperatures. We have provided evidence that the nest construction behavior of open-cup-nesting birds systematically varies in response to large-scale spatial variation in spring temperatures.
authors.affiliation: Department of Biological Sciences, Macquarie University Sydney, NSW, 2109, Australia.
authors.forename: Mark C
authors.initials: MC
authors.lastname: Mainwaring
authors.affiliation: Department of Biological Sciences, University of Lincoln Riseholme Park, Lincoln, LN2 2LG, UK.
authors.forename: D Charles
authors.initials: DC
authors.lastname: Deeming
authors.affiliation: Lancaster Environment Centre, Lancaster University Lancaster, LA1 4YQ, UK.
authors.forename: Chris I
authors.initials: CI
authors.lastname: Jones
authors.affiliation: Lancaster Environment Centre, Lancaster University Lancaster, LA1 4YQ, UK.
authors.forename: Ian R
authors.initials: IR
authors.lastname: Hartley
keywords: Insulation quality; Turdus merula; latitude; nest composition; nest size; spring temperature