Do Great TitsParus majorNesting at High Altitudes Build Better Insulated Nests?

Abstract

We investigated nest building behaviour of great tits Parus major in relation to altitudinal temperature gradients in Lower Austria. We hypothesised that colder environments at higher altitudes would select for a nest construction that increases thermal nest insulation. We collected data on nest architecture from 11 nests and on nest components from 33 nests along an altitudinal range (390 m) in 2010 to 2012, and experimentally measured specific insulation quality in 11 highly variable nests. Highly insulated nests included significantly more feathers than less well-insulated nests. Despite significantly lower temperatures at high altitude than at low altitude sites before clutch initiation, nest insulation quality did not increase with altitude. Moreover, we found that the date of clutch initiation was positively correlated with altitude. Birds may adjust to lower spring temperatures at high altitude by delaying clutch initiation, thus avoiding the need to invest in gathering highly insulating material.