The feeding ecology of giraffe (giraffa camelopardalis linnaeus) in nairobi national park, and the effect of browsing on their main food plants."

Abstract

The research described in this thesis was carried out between June 1968 and May , 1969 in an area of approximately 10.14 square kilometres in the plains of'Nairobi 'National Park. Of this area abo~~ 4074 square kilometres are covered by vegetation suitable for giraffe browsing. From vegetation and giraffe distribution maps that were prepared it is evident that Acacia drepanolobium savanna and woodland/thicket are the main feeding zones for giraffe. The density of giraffe in the area was approximately one per square kilometre. When browsing? giraffe either break off twigs with their tongues or bite off separate leaves with their teeth. All types of trees bushes and f,orbs are eaten? but long strands of vegetation are not able to be ingested It was found that giraffe spend 50 - 100 secollds browsing each bush of A .•drepanolobiumo The exact time spent browsing on this speciesp and others, is dependant upon the number of young shoots availble per tree The shape of the different small trees and bushes also affects the browsing time. Generally less browse is available on ,an individual flat topped apecfea such as !.drepanolobium than on II other more rounded bushes; -therefore a longer period of time is spent browsing each bush of the latter type. An average of 557 shoots per hour of A.drepanolobium are eaten during continuous feeding. The browse also provides most of the water a giraffe requires, and drinking was rarely seen. Rumination periods last from a few minutes to over an hour. The longest period of rumination seen was for 75 minutes. Chewing is at the rate of about one chew per second The daily activity from month to month was very variable9 but a basic feeding pattern was recognized. At daybreak there was little feeding activity but by 07000 hours feeding reached a peak for the daY9 7701% of all activity at this time was feeding This level decreases through the morning to a minimum of feeding just after noon. During the afternoon and evening feeding steadily increases again Giraffe spent on average 63.9~ of the day feeding The amount of ruminating is inversely related to browsing, and the peak rumination period is between 12.00 and 13000 hours During the study, as a whole9 13.2% of the day was spent ruminating. The remaining 2289% of the d~y was filled by "other activities" such as walkingp which activities occur~ed at a constant level throughout the day. During the hours of darkIII 'ness browsing appeared to be much r-e duc ed , The commonest plant in the area was A.drepanolobium which was also the key browse species and 60.7% of all browsing was on this species. Contrary to popular belief the long neck of the giraffe is not necessarily used for browsing tall trees and if more succulent browse is available at a level below head height this will be chosen. The commonest height at which feeding was seen was between 0.5 - 2.0 metres, and this category included the majority of A0drepanolobium bushes. Changes in the weather during the wet season can cause a shift in the diet from A.drepanolobium to other larger bushes and the height at which feeding occurs as correspondingly r-af aed , As the young browse is removed from the tops of the bushes the height of feeding become. lowero During the dry season when there was little succulent browse available Aedrepanolobium was again the main browse species. ·There was maximum browsing on !.drepanolobium when precipitation was such that new growth was stimulated but the firm condition of the clay soil did not deteriorate and hinder v ceased in both these species From experimental ex closures it was snown tha'~ browse production of ~oglabra a~ 4-,,0 metr..,s was greater than that at .200 metres on the same busho It was estimated that-female giraffe consume about 607 kilograms of green browse per day~ It seems that provided that the habitat is maintained in its present state 1 and provided that the movement of giraffe is not restricted there will be no danger from over browsing.