ECOLOGICAL FACTORS INFLUENCING SEXUAL SEGREGATION AND GROUP-SIZE IN FALLOW DEER (DAMA-DAMA)

Grouping patterns in fallow deer Dama dama were studied between 1986-9 by direct observation from transects of eight populations in the New Forest and adjacent agricultural land in southern England. Study popul ations were chosen on the basis of pronounced differences in populatio n density, sex ratio, and dispersion, and differences between the site s in habitat availability and patterns of habitat use. Within both for est and agricultural study sites, a large majority of female deer was observed in single sex female groups throughout the year. The lowest l evels of female segregation occurred during the autumn reproductive pe riod. Males generally exhibited lower levels of sexual segregation tha n females, particularly during winter and spring In the forest sites, winter and spring mixed-sex groups were largely the result of young ma les joining female feeding aggregations. In contrast, mixed-sex groups in agricultural sites contained mature males throughout the year and were not exclusively based on habitats used for feeding. There was a n egative correlation between the extent of winter and spring male segre gation and population sex ratio, suggesting that males join female gro ups when male densities are relatively low. Female group size varied s easonally in all sites, attaining maximum values in winter or spring a nd minimum values in summer or autumn. This was not a reflection of ch anging patterns of habitat use; group size varied seasonally in both o pen and closed habitats. Female groups were larger in open habitats th an in closed habitats throughout the year. The size of female groups v aried between the study sites but there were no clear differences in o verall female group size between the forest and agricultural sites. Th ere was a tendency for open habitat group size to be largest in the fo rest sites and closed habitat group size to be largest in the agricult ural sites. Female group size overall was unrelated to the proportion of each site occupied by closed habitat. However, an increase in the a mount of closed habitat was reflected by a decrease in closed habitat group size. Female group size overall was negatively related to the us e of closed habitat; not surprisingly, an increase in use of open habi tats resulted in increased overall group size. Female group size overa ll was not related to density; large groups occurred in both high and low density sites. However, in high density populations, open habitat group size was larger and closed habitat group size smaller than in lo w density populations.