Patterns of variation in waterbird numbers on four Rift Valley lakes in Kenya, 1991–1999

摘要: Waterbird populations were censused each January from 1991 to 1999 at Lakes Naivasha, Elmenteita and Nakuru 1992 Lake Bogoria. These shallow lakes in the Kenyan Rift Valley fluctuate greatly water level alkalinity. All but Naivasha are usually saline; times support fish, while Bogoria is fishless. A standardized logarithmic index of relative abundance (value 1.0 for mean) was calculated major waterbird group lake, combined (‘combined lakes’). Its variance used compare levels variation within across lakes. For lakes, there high large piscivores (whether or separated into groups), grebes, rallids flamingos. There low Palaearctic waders (combined ibises spoonbills birds prey. However, generally showed idiosyncratic patterns different groups. Variance indices prey kingfishers consistently (max. 0.036 0.042, respectively), no had all sites. The (other than flamingos) (0.018 – 0.085) similar (0.018). flamingos five higher other (p<0.05), though two variances almost equal Flamingos most variable (variance 0.281) followed by (0.177), (0.101) (0.024, significantly lower rest, p<0.05). This opposite order mean numbers recorded site. Large relatively stable 0.005) much more (0.199) (0.269). Patterns correlated some groups, such as Nakuru. correlations could be related local ecological conditions. few sites, these mainly direct. was, therefore, evidence that a fixed population waterbirds distributing itself sites according Each lake thus seems represent independent entity, they host evidently move widely afield this portion Valley.