The Population Structure and Foraging Behavior of Reticulated Giraffe (Giraffa Camelopardalis Reticulata) at Garissa Giraffe Sanctuary, Garissa County, Kenya

Abstract

A study of how animals make decisions while foraging is fundamentally important as it informs habitat management decisions and assessment of species distribution and home ranges. In deciding what to eat, herbivores seek to maximize food intake while avoiding or minimizing ingestion of toxins that plants use to defend themselves against herbivory. Plant chemical compounds, such as tannins, gums, and alkaloids as well as nutritional value (e.g., protein, fiber content) have been identified as broadly important factors in the diet selection of herbivores. However, diet selection in wild herbivores is influenced by many other factors, which are poorly understood. This study investigated the population characteristics and foraging ecology of the endangered reticulated giraffe in Garissa Giraffe Sanctuary, in Garissa County, Kenya. The specific objectives were to assess the population characteristics, determine their diet and its quality, and their foraging behavior within and around the sanctuary. Data were obtained through field surveys conducted by closely following distinct family groups, whose members were photographed and identified using a GiraffeSpotter. Various methods including field surveys for giraffe density and population estimates through distance sampling and photographic mark-recapture techniques were also used respectively. Observations of foraging behaviour and food preference were conducted using instantaneous scan sampling technique. Samples of available food plants were obtained, and their nutritional value determined through laboratory analysis at the University of Nairobi. The results indicated that a total of 621±105 (SE) reticulated giraffes were resident in the sanctuary but there was considerable movement of giraffes into and out of the sanctuary. The density of giraffes in the sanctuary was 4.98 ± 1.88 (SE) giraffes’ km 2. The population sex structure was skewed towards females with sex ratio of 38 males to 68 females. This population sex structure indicated high potential for the resident giraffe population to increase. Moreover, the reticulated giraffes are obligate browsers and fed on a variety of trees and shrubs, especially those of Acacia tortilis and other shrub species growing along the valleys of seasonal streams in the sanctuary and the River Tana flood plain. Their diet did not change significantly among the four selected study sites in the sanctuary. The reticulated giraffes in the sanctuary fed on a high-quality diet of twigs, leaves, and shoots of native plant species. However, the alien invasive species (Prosopis juliflora) and the locally invasive species (Acacia reficiens) are rapidly spreading in the giraffe foraging habitat and gradually encroaching the native food plants. The two invasive plants were not significantly represented in the diet of the reticulated giraffes. However, this does not preclude their potential importance in the diet of the reticulated giraffes in future. The invasion of the sanctuary by the two invasive plant species and the continued poaching of giraffes venturing outside the reserve threaten the future of the resident population. It is recommended that the giraffe population in the sanctuary be more effectively protected and tagged for regular monitoring. Further, deliberate efforts should be made to eliminate or control the spread of the two invasive plant species as well as effectively control livestock use of the reserve, which act as dispersal agents of the invasive plant species in the sanctuary and farther away.