Effects of Geographic Location and Habitat on Breeding Parameters of Great Tits

Abstract

Studied variation in laying date, clutch size, and number of fledglings in Great Tits (Parus major) in relation to habitat, elevation, and latitude using data from 137 breeding areas. Laying date was not affected by habitat type but increased with elevation and showed a significant quadratic relationship with latitude. Food availability, ambient temperature, and photoperiod together can explain why laying date increases with latitude. However, more information is needed to understand why birds in northern Africa start laying later than in nearby southwestern Europe. Variation in clutch size and number of fledglings was significantly affected by habitat type, with lower values in coniferous forests. Mean clutch size decreased with elevation. Mean clutch size and mean number of fledglings of first and second broods showed a significant quadratic relationship with latitude, with the highest values at about 55 to 60 degrees N. The results suggest that latitudinal variation in life-history parameters is related to variation across marginal and central parts of the species' distribution and is influenced by factors such as daylength, temperature, and/or seasonality of food resources. Birds at southern latitudes are probably under lime constraints, whereas birds at northern latitudes are probably under energy constraints. Alternatively, Great Tits at northern latitudes might be less well adapted to these habitats because they invaded northerly latitudes during the last decades. The proportion of pairs laying a second clutch decreased with latitude. The observed pattern of a late start of laying, lower variability in laying date, and lower frequency of second clutches in northern populations likely was due to the late and short growing season for the Great Tit's main prey caterpillars.