Local Temperature and not Latitude Determines the Design of Blue Tit and Great Tit nests

Recent studies are documenting the extent to which the mass and construction of bird nests varies between individuals and locations. In the Blue Tit (Cyanistes caeruleus) and Great Tit (Parus major), temperatures experienced by females during nest construction are inversely related to nest mass. Moreover, Mainwaring et al. (Journal of Biogeography, 2012) showed that nests constructed at high latitude are heavier and better insulated than nests built by conspecifics in the south. Although mean spring temperature was used as a proxy for latitude in the Mainwaring et al. study, it remains untested whether individual birds build nests in response to a narrower range of temperatures experienced at the start of the breeding season. Our study showed that irrespective of latitude nest mass, and in particular nest cup mass, of Blue Tits and Great Tits was significantly affected by the temperature experienced by the birds for the seven days preceding clutch initiation. Similar results were seen with the insulatory properties of nests. The potential impact of variation in nest construction and insulation on subsequent incubation and chick-rearing behaviour is discussed.