Incubation Attentiveness and Nest Insulatory Values Correlate in Songbirds

The behaviour of the incubating bird should be linked with the functional characteristics of its nest because they could minimise the incubation period that will reduce the risk of predation. Incubation attentiveness (percentage of daylight hours) in small passerines is a highly variable behaviour that is unrelated to egg mass. The thermal characteristics of nests are known to vary but whether they correlate with attentiveness, i.e. high attentiveness could reflect poorly insulated nests, has yet to be investigated. In this study, insulatory values were determined using temperature loggers for five species of British songbird in order to supplement equivalent data for six species from published sources. Attentiveness values for each species were determined from the literature. There was a significant negative correlation between attentiveness and insulatory values, which was unaffected by phylogeny. By contrast, attentiveness did not correlate with female body mass. That the avian incubation behaviour correlates with the functional properties of bird nests supports the concept of a bird–nest incubation unit, where reproductive success depends on both the bird and the nest structure. Further research should be directed towards a better understanding of this relationship for more species and, given the observed plasticity exhibited in nest composition and function, within species.