| dc.description.abstract | A study was carried out to obtain information on behaviour, social organisation, movement pattern,
feeding habits and population dynamics of the Maasai giraffe (Giraffa camelopardalisi on Game
Ranching Limited (GRL), Athi River, Kenya; and to use modelling and simulation techniques to
assess different options for harvesting the GRL's giraffe population. An existing giraffe photo-file
was regularly updated during the course of the study. Individually known focal giraffes were
followed for periods of 6 or 12 hours during daytime and their activity budgets continuously
recorded. Activities recorded included: walking, feeding, standing, lying, drinking, running, urine
testing, fighting and suckling. The names of other giraffes accompanying the focal individual, its
location, vegetation type and catena were recorded at half-hour intervals. Browse production by
Acacia drepanolobiwn, Acacia seyal and Acacia xanthophloea, and Balanites glabra and its
consumption by giraffe were studied. The study found that feeding, walking and resting (standing
and lying) constituted more than 95% of the giraffe's daytime activity budget. Males spent more time
walking and resting while females spent more time feeding. Females spent 67% and males 39-54%
of their daytime feeding. Both males and females spent more than 90% of their feeding time
browsing on A. drepanolobium, A. seyal, A. xanthophloeaand H. glabra. Females and young
allocated 67-84% and males allocated only 23-34% of their browsing time to feeding below their
shoulder height. This height differentiation was also accompanied by a marked female preference for
A. drepanolobium, leading to resource partitioning, a factor that reduced competition between the
two sexes. Axanthophloea, A. seyal and B. glabra showed clear signs of over-browsing by giraffe,
but A. drepanolobium didn't. Browse availability of on A. drepanolobium, A. seyal, A. xanthophloea
and B. glabra exhibited seasonal fluctuations, being 1I10st abundant two months after the rains
commenced and most scarce towards the beginning of the following rainy season. GRL's giraffe
responded to this fluctuating food availability by forming two sub-populations, adjusting time spent
on feeding, walking and resting and, adjusting their daily movement pattern. The seasonal variation
in birth and death rates of the GRL's giraffe population and the frequent occurrence of population
crashes after prolonged droughts documented in this study were also attributed to the seasonal
fluctuations in browse availability. Annual calf mortality during the study period was about 17%,
while sub-adult and adult mortality was less than 2%. Average calving interval, on the other hand,
was 21.5 months. The annual growth rate of GRL's giraffe population was estimated at 10.2%,
suggesting a giraffe population growing at almost its maximum potential growth rate. The analysis of
browse availability, on the other hand, suggested a population at its habitat's carrying capacity. These
two findings casted doubt about the suitability of the logistics population growth model (Seidl and
Tisdell 1999) in describing the growth pattern of the GRL's giraffe population. This study therefore
concluded that the J-curve and not the logistics model best describes the growth pattern of GRL's
giraffe population. The modelling confirmed 'the notion that age-selective harvesting has little effect ,
in improving sustained yield whether the latter is measured in terms of animals killed, kilograms of
meat sold or financial returns. The only exception is when the products from the different age classes , ,
vary in their market value. Male-biased harvesting, on the other hand, increased sustained yield by
26-48%. Benefits accruing from male-biased harvesting were a Tunction of how far the sex ratio is
skewed in favour of females. Maximum sustained yield was achieved at a sex ratio of one male to
nine females. | en |
