Group size and composition are correlated with population density in the group-territorial blue korhaan (Eupodotis caerulescens)

The blue korhaan (Eupodotis caerulescens) is a poorly known bird endemic to the grasslands of southern Africa. It lives in permanently held territories defended by groups of individuals. During 2001 and 2002, 61 transects were carried out along 544 km of roads in Mpumalanga province (South Africa) to collect data on territory density and group size and composition in this species. Habitat, altitude and topography variables were measured to evaluate their influence on population density. Average territory density was 1.56 +/- 0.19 (SE) territories per 5 km and maximum densities attained 5.6 territories per 5 km. Within its area of occurrence, higher densities occurred along transects with larger proportion of short grassland (either burned or grazed) and flatter topography. Mean group size was 3.03 +/- 0.11 birds (n = 119), with 87.4% of the groups having one to four birds. Most common group composition was one male and one female-like (34.5%), followed by two male and one female-like (17.2%) and two male and two female-like (13.8%). Single individuals were always males, and the male/female-like ratio peaked at a group size of three and decreased thereafter. Mean group size increased with territory density (r(s) = 0.42, P = 0.007, n = 41). There were no differences in group size across habitat types. The occurrence of habitat saturation and cooperative breeding in this species could explain the observed results.