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Habitat selection and social group dynamics of African elephants in Amboseli, Kenya

University of British Columbia

The selection and use of habitats by African elephants were examined in relation to vegetation abundance and elephant social grouping patterns. I conducted the study in the Amboseli basin and surrounding semi-arid bushlands in southern Kenya from November 1978 to October 1979. Elephant habitat distributions in the basin in 1978/79 were monitored in a series of 88 ground surveys, while data from 54 aerial counts from 1975 to 1980 were examined for a longer term view. Plant density and biomass were monitored in permanent vegetation plots located in different habitat types in the Amboseli basin and bushlands. Habitat types were defined, described, and compared. Herbaceous (grass/forb) biomass was more abundant than browse (twig/leaf) biomass at all times within habitat types, but in the dry season, the woody -layer of some habitat types, such as the swamp edge woodlands and dense bushlands, was more abundant than the herb layer of other habitats, such as the open grasslands. Bushlands and woodlands had highest diversity of herbaceous and woody biomass. Biomass production was significantly related to wet season rainfall in all habitats. The herb layers of swamp edge habitats consistently had the highest biomass and lowest nutritional quality (exemplified by crude protein content), and were abundant well into the dry season. Woodland and bushland habitat types had herb layers which were only seasonally abundant, but of higher protein content through the year. Elephants preferred woodlands (and, in drier years, bushlands) in the wet seasons and swamps in the dry seasons. Elephant numbers in the woodlands and grasslands were positively related to monthly rainfall and herb layer biomass, and numbers in the wet swamps and in the swamp edge grasslands and woodlands were negatively related to the same variables. There was a large amount of variance associated with these relationships. The ranking of habitat use by elephants was significantly correlated with the ranking of herb layer biomass across habitats in the dry season, but not in the wet season, when less abundant, but more nutritious, vegetation was available in the woodlands and bushlands. There were no clear relationships between elephant numbers and browse biomass or percent woody cover across habitat types. Groups of cows and calves were larger in the the rainy seasons, and in years with higher rainfall, and smaller in low rainfall seasons and years. Bachelor bull groups showed some similar patterns but group sizes and the range of variation were always fairly small. There was an apparent shift by the larger cow/calf groups to the high biomass habitats, and possibly more open habitats, with changes in plant abundance in the dry season. The number of large groups was not correlated with elephant density in habitat types. This supports the hypothesis that large social group size is maintained by habitat selection, rather than random encounters of groups. The larger bachelor bull groups did not shift habitats in this way. Although their habitat use patterns were similar overall, bachelor bulls used the wet swamps and open woodlands more in the dry season while cow/calf herds preferred the open woodlands more in the wet seasons and swamp edge grasslands more in the dry seasons. Explanations of these differences relating to physiological and social differences between the gender classes were offered. Elephant habitat selection strategy appears to consist of a "stable element" centered on the predictable dry season habitats and an "opportunistic element" in less predictable, but more profitable, wet season habitats.

Text

2010-04-13

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http://hdl.handle.net/2429/23387

Zoology

University of British Columbia

Graduate