Population Status, Feeding Ecology and Activity Patterns of Grants Gazelle (Gazella granti) in Abijata-Shalla Lakes National Park, Ethiopia
Information on population status, feeding ecology and activities of Grants gazelle (Gazella granti) was collected from January to August, 2010 by means of total count and direct observation. Data were analysed using descriptive statistics, Chi-square test and one way ANOVA. Tukey multiple comparison test was also used to test variation between different activities. The average number of Grants gazelles in the study area was 78 during the dry season and 59 during the wet season; mean group size was 2.36±0.07 and 2.70±0.1 during the wet and dry seasons, respectively. Grants gazelles were observed feeding on grasses, herbs, trees and shrubs. The food items consumed by Grants gazelles between dry (p<0.05) and wet (p<0.05) seasons differed. Grants gazelles graze more often than browse during both seasons. They frequently fed during early morning and late afternoon. Activity budgets differed seasonally (wet season: p<0.05; dry season: p<0.05). They spent 42.9% of their time on feeding during the wet season. On the other hand, during the dry season, 35.8% of their time spent on resting followed by feeding (29.7%). Different conservation measures should be taken in to consideration to enhance the number of Grants gazelle and to create suitable habitat for them.
December 09, 2011; Accepted: February 14, 2012;
Published: March 06, 2012
Grant's gazelles (Gazella granti, Brooke, 1872) are larger in size than
other gazelles. Adult males weigh 60-81 kg and females weigh 38-67 kg (Kingdon,
1997). Both sexes have horns but males have longer, thicker and highly ringed
horns (Kingdon, 1997). Grant's gazelles are distributed
in Sudan, Ethiopia, Kenya and Tanzania (Nowak, 1991).
They inhabit open grass plains and are frequently found in shrub land. They
also occur in semi-arid areas (Arctander et al.,
1996). They occupy plains during the dry season and reside in woodlands
during the wet season. They are territorial and migratory animals (Estes,
Grants gazelles are generally mixed feeders (browse and graze) (Oindo,
2002). They feed on herbs and shrubs during the late wet and dry seasons
(Kingdon, 1997). As they derive most of their moisture
from the plants they eat, they can stay without water for long period of time
(Walther, 1972). They are gregarious. However, size
and composition of their social groups are affected by external ecological factors
such as habitat, seasonal changes and availability and quality of food (Estes,
1991; Gerard et al., 2002). The size and
composition of groups are the basic elements of their social organization (Raman,
1997). They have several social groups including females and offsprings,
bachelor males, mixed herds and dominant males. The average herd size is about
30 (Stuart and Stuart, 1997). Females form groups consisting
of nursing mothers and their offspring. Bachelor groups consist of adolescent
and older males without territories (Walther, 1972).
Territorial males lead all females that enter the boundary and guard these during
estrus to prevent other males from mating (Walther, 1991).
On average, territorial males are older, larger and have thicker horns than
bachelor males (Stelfox et al., 1984). The dominant
males mark their territory with urination and defecation (Estes,
1967). Grooming is an essential part of the gazelles behavior because, it
prevents parasites from becoming distended in their skin and improves overall
health (Hart, 1992).
The most common predators of Grant's gazelles are jackal (Canis aureus),
cheetah (Acinonyx jubatus), leopard (Panthera pardus), spotted
hyena (Crocuta crocuta) and wild dog (Lycoan pictus). Grants
and Thomsons gazelles frequently intermix as both species benefit from
the enhanced vigilance (Fitzgibbon, 1990). Grants
gazelles are classified as a species of least concern, the majority of species
and subspecies within this genus are considered to be threatened, endangered
or extinct. Reduction in gazelle numbers is attributed to habitat loss, unregulated
sport hunting and the bush meat trade (Nowak, 1991). Limited
research has been conducted on Grants gazelle in Ethiopia and even in
Africa. Especially, there is no documented information in ecological and other
aspects of Grants gazelle in Abijata-Shalla Lakes National Park. Therefore,
the present study can fill part of the gap. The major objectives of this study
include: (1) to identify the feeding behavior of Grants gazelle, (2) to
show their diurnal activity pattern, (3) to reveal the current population status
and (4) to show sex and age structure of Grants gazelle in Abijata-Shalla
Lakes National Park, Ethiopia.
MATERIALS AND METHODS
Study area: Abijata-Shalla Lakes National Park is encompasses Lake Abijata
and Shalla and surrounding lands (Fig. 1). The Park located
about 200 km from Addis Ababa in the Ethiopian Central Rift Valley and covers
a total area of 887 km2, elevation ranges from 1540 to 2075 m above
sea level (EWNHS, 1996). The Park comprises different
lakes with varying shoreline and woodland vegetation (Tefera
and Almaw, 2002). It was established predominantly as a bird sanctuary in
1971 (EWNHS, 1996). The islands are home to breeding colonies
for many birds. The rift floor is fed by perennial rivers originating from adjacent
highlands both to the east and west (Ayenew, 2001).
The climate of Abijata-Shalla Lakes National Park is classified as upper kola.
Annual rainfall averages about 500 mm and is most prominent during March, April,
June and September (CPI, 2000). The average annual temperature
is 20.1°C with a maximum of 26.6°C and minimum of 13.5°C (EWNHS,
1996). The type of soil in the area is alluvial and very fine in nature;
major vegetation types include Acacia savanna covering most hills and
shorelines, Euphorbia woodland, riverine vegetation, bushland, shrub
and grassland. Dominant trees of the Acacia woodland include Acacia
tortilis, A. Senegal, A. seyal and A. gerrardii, Balanites
aegyptica, Grewia bicolor, Ficus lutea, Ficus sycomorus
and Maytenus senegalensis (Tefera and Almaw, 2002).
According to Hillman (1993), 403 species of birds and
76 species of mammals have been recorded in the Park. The Park is one of the
narrowest parts of the Great Rift Valley, a major flyway for both Palearctic
and African migratory birds, particularly raptors, flamingos and other water
birds (Birdlife International, 2009).
|| Map of Abijata-Shalla Lakes National Park, the study area
and census blocks
Population census: To estimate the population size of Grants gazelle
in the study area, total count method employed during both dry and wet seasons
following Caughley and Sinclair (1994) and Sutherland
(1996). The identified ranges of Grants gazelle were classified into
five different blocks based on artificial and natural boundaries. Census was
conducted during early morning and late afternoon in each block during both
wet and dry seasons repeatedly. Counts were carried out within 2-3 h using unaided
eyes and/or 12x40 binoculars. During the census period, detailed information
on the herd was collected. This enabled to categorize the population according
to their responsive ages. The categories included adult male and female, sub-adult
male and female, unidentified juvenile sex (Knight, 1970;
Bergerud, 1971; Lewis and Wilson,
1979). The total number of individuals in a group was counted to identify
the group size. Furthermore, habitat type was also recorded to identify their
habitat preference. Animals were treated as the same group if the separation
distance is approximately less than 50 m (Hillman and Hillman,
1987). Repeated counting of the same herd or cluster was avoided using recognizable
features such as cluster size, harem composition and distinct individuals with
body deformities such as cut tail or ear (Wilson et al.,
Feeding ecology: Repeated standard observations were used to collect
data on foraging behavior following Hartley (1953).
Time spent for foraging was also recorded using focal sampling (Sutherland
et al., 2005). Focal sampling consisted of watching an individual
for a fixed period (10 min) with unaided eye or binocular according to the size
and the distance of the animal from the observer and recording the activities
such as the type of food items consumed and amount of time spent for foraging.
Parts of the plant species consumed were classified as green leafy twigs, non
green leafy twigs, brown leafy twigs, brown twigs, green leafy grass stems,
non green leafy grass stems, brown leafy grass stems and tree pods. Furthermore,
foraging types including browsing and grazing were also recorded during both
wet and dry seasons. Plant samples were collected from the study area and pressed,
then taken to Addis Ababa University herbarium for identification.
Activity patterns: To study the activity patterns of Grants gazelle,
scan sampling method was employed (Altmann, 1974). Focal
individual was randomly selected by stratifying based on age and sex. When the
focal animal was in a group, the dominant activity in the group recorded at
the beginning of the observation. Activities included feeding, walking, resting,
mating, self-grooming, mutual grooming, nursing, suckling, running, chasing,
fighting and social interaction. Observations carried out for five min at an
interval of 15 min from 06:00-18:00 h; activities displayed and durations continuously
recorded using a stop watch.
Data analysis: Data analyzed using SPSS software version 17 and Microsoft Excel. Descriptive statistics were used to report the Grants gazelle population size. Food items used were compared using a Chi-square test across seasons. Activity patterns also compared within a day and between seasons using a one-way ANOVA to test differences among hourly time budget over both seasons. Tukey multiple comparison tests applied to test variation between different activities per h within a day.
The maximum number of Grants gazelle recorded was 78 during the dry season and 59 during the wet season (Table 1). On the other hand, the maximum group size consisted of 17 and 20 individuals during the dry and the wet season, respectively. These include adult males and females, subadult males and females and juveniles. Groups of bachelor males also consisting up to 15 individuals were also recorded. The mean group size was 2.36±0.07 during the wet season and 2.70±0.1 during the dry season.
Of the total individuals sighted in the study area, 21.87% constituted adult males, 43.27% adult females, 15.68% subadult males, 9.08% subadult females and 10.1% unidentified juveniles. The number of animal groups significantly differed during the dry (χ2 = 32.74, df = 4, p<0.05) and wet (χ2 = 93.13, df = 4, p<0.05) seasons. Adult female groups constituted the largest groups during the wet (25.11%) and dry (34.6%) seasons, whereas subadult females were lesser in number among groups during both the wet (4.25%) and dry (8.3%) seasons.
Age and sex ratios differed (p<0.05) between seasons (Table 2). The sex and age ratio of subadult females and adult females were greater during both the dry (1.00:4.17) and the wet (1.00:6.00) seasons.
|| Number of Grants gazelles recorded during wet and dry
|| Sex and age ratio of Grants gazelles during wet and
|| Relative percentage of plant species consumed by Grants
gazelles during wet and dry seasons
Grants gazelles were observed feeding on 16 different plant species in 10 families during the study period. Plant species consumed were grasses, herbs, trees and shrubs. Cenchrus ciliaris (26.7%) was the most frequently consumed food item by Grants gazelle followed by Erucastrum abyssinicum (17.8%), whereas Ritchiea albersii (0.7%) was the least consumed during the dry season. On the other hand, Cenchrus ciliaris (24.8%) was the most frequently consumed food item and Bidens biternata (1%) and Rhoicissus tridentate (1%) were the least consumed food item during the wet season (Table 3). There was a significant difference in food items consumed between dry (χ2 = 74.79, df = 13, p<0.05) and wet seasons (χ2 = 103.47, df = 11, p<0.05).
Of the diet during the wet season, 54.8% constituted green leafy twigs followed by green leafy grass stems (37.5%). Grants gazelles were not observed feeding on brown leafy twigs, brown twigs and tree pods during this season. During the dry season, they consumed green leafy twigs (34.6%) and brown leafy grass stem (19.9%) but were not observed feeding on brown twigs (Fig. 2).
Grants gazelles browsed 28.9% of their time during the dry season and 31.7% during the wet seasons and grazed 68.3% of their time during the wet season and 71.1% during the dry season. Browsing decreased over the dry season as grazing increased. There was a significant variation in the proportions of grazing and browsing between dry (χ2 = 24.06, df = 1, p<0.05) and wet (χ2 = 13.55, df =1, p<0.05) seasons.
Diurnal feeding behavior of Grants gazelle was greatest between 6:00-7:00 h and 17:00-18:00 h during both wet and dry seasons. Feeding frequency was least between 9:00-10:00 h during the wet season (Fig. 3).
Overall, Grants gazelles spent 42.9% of their time on feeding, 25% on
resting and least time on mating (0.2%) and social interactions (0.2%) during
the wet season.
||Plant parts preferred by Grants gazelles and their percentage
in the study area during the dry and wet seasons (GLT: Green leafy twigs,
NGLT: Non green leafy twigs, BLT: Brown leafy twigs, BT: Brown twigs, GLGS:
Green leafy grass stem, NGLGS: Non green leafy grass stem, BLGS: Brown leafy
grass stem and TP: Tree pod)
|| Seasonal feeding pattern in the study area within different
||Percentage of different activities conducted by Grants
gazelles during the wet and dry seasons
Fighting (1.9%) was only observed during the wet season whereas nursing (1.5%)
was only observed during the dry season. On the other hand, 35.8% of their time
was spent resting followed by feeding (29.7%). The least amount of time spent
on mutual grooming (0.7%) during the dry season (Fig. 4).
Hourly time budget differed significantly over both seasons (wet season: F11
412 = 1.82, p<0.05; dry season: F11 595 = 4.28, p<0.05).
Multiple comparison tests showed significant differences among h of the day.
During the dry season, a significant difference (p<0.05) was observed between
2:00-3:00 h and 6:00-7:00 h and 11:00-12:00 h.
During the dry season feeding showed two peaks for both adults and juveniles in the early morning (6:00-7:00 h) and late afternoon (17:00-18:00 h). It was least at 13:00-14:00 h for all the three age groups and greatest for juveniles in the late afternoon (17:00-18:00 h) during the wet season. Feeding was less frequent during 9:00-10:00 h for adults and subadults. On the other hand, resting activity peaked for adults at 9:00-10:00 h while juveniles rested more frequently at 16:00-17:00 h during the dry season. Juveniles showed almost no resting pattern in the morning (6:00-7:00 h and 7:00-8:00 h), mid day (11:00-12:00 h) and late afternoon (17:00-18:00 h). During the wet season, resting pattern was identified by highest peak at 12:00-13:00 h for subadults, juveniles and adults, respectively. However, very low resting pattern was recorded between 15:00-16:00 h and 17:00-18:00 h for all the three animal groups.
Monitoring populations of wild animals is essential for sustainable management
(De Paul and De Clercq, 2009). According to our survey,
the average number of Grants gazelle decreased from 78 (dry season) to
59 (wet season) in the study area. This could be related to increasing the existence
of cattle in the study area during the wet season. The displacement of herdsmen
from the Afar region and other areas may be displacing Grants gazelles
from their original habitat. Similarly, according to Dunham
(2001), mountain gazelle populations are affected due to domestic livestocks
in central Arabia. Generally, mammalian herbivores are important components
of many terrestrial ecosystems (Olff et al., 2002)
and human interventions are causing major changes in composition of herbivore
assemblages across the world. With the intensification of pastoralism, herbivores
have become severely depleted both in diversity and abundance in many parts
of the world (Prins, 1992). Therefore, for future research
in our study area, use of telemetry may be a better method to locate missing
One of the advantages of living in groups is that individuals may need to be
less vigilant, allowing them more time for other important activities such as
foraging (Shorrocks and Cokayne, 2005). In this study,
the maximum group size of Grants gazelle was recorded during the wet season,
probably due to increased availability of food. Similarly, a research conducted
in China indicated that gazelles gathered together and formed larger herds in
areas where they found enough suitable food (Qiao et
al., 2011). The number of animal groups differed during seasons. Groups
of adult female Grants gazelles were more abundant than other age groups
followed by adult males. This could provide an opportunity to increase populations
of the Grants gazelle at Abijata-Shalla Lakes National Park provided the
area of protected habitat is enlarged. Furthermore, bachelor male groups were
common during the wet season, reflecting social and breeding behavior.
According to our result, Grants gazelle foraged on over 16 different
species of grasses, herbs, trees and shrubs. However, there were seasonal differences
in food items consumed. Similarly, a study conducted in Kapiti ranch (Kenya)
indicated that Grants gazelles tended to have a wide variety of plant
species in their diets (Kilonzo et al., 2005).
Food availability and preference may be the major reasons for the seasonal variation
in food items consumed. The grass Cenchrus ciliaris was the most commonly
consumed food item by Grants gazelle during both seasons. During the wet
season, it was difficult to identify the type of shrubs and herbs consumed by
Grants gazelle due to their diverse nature so that they were grouped as
shrubs and herbs. Shrubs and herbs constituted 22.8% of the diet of Grants
gazelle during the wet season. This might be due to easy digestibility of shrubs
and herbs. They were observed feeding the different parts of plants during both
dry and wet seasons. However, they avoided tree pods and brown leafy twigs during
both seasons. Because, according to Woie (1984), green
parts are more nutritious with high moisture content and easily be digested
due to low fiber content as opposed to the dry parts. The present study identified
Grants gazelles as more grazers than browsers. However, Spinage
et al. (1980) reported as opposed to this pattern which means more
browsers than grazers. These differences probably related to the availability
of food in our study area. Diurnal feeding behavior indicated that Grants
gazelles were mostly active during early morning and late afternoon. They devoted
more time for feeding during the wet season. Similarly, Grier
and Burk (1992) concluded that feeding is the most important activity for
all organisms in which they devoted most of their time. However, Grants
gazelles spent most of their time with resting followed by feeding relative
to other activities conducted during the dry season. This is likely related
to the high diurnal temperatures during the dry season and consequently, the
need for shelter to overcome heat stress and water loss (Belovsky
and Slade, 1986; Stark, 1986). The biodiversity
of Abijata-Shalla National Park has been declining from time to time (Gobena,
2008). Although the Park is 887 km2, it is highly disturbed from
extensive agriculture, human settlement, firewood collection and charcoal production
and overutilization of water from Lake Abijata for caustic soda factory. A 1
km2 fenced area used to be utilized for ostrich farming harbors the
majority of the Grants gazelles due to the existing threats. In East Africa,
many conservation areas do not encompass whole ecosystems (Okello,
2005). Consequently, variations in wildlife numbers, especially herbivores
observed within confined protected areas are common, because their natural ranges
do not extend well beyond the boundaries of the protected areas particularly
for the fenced protected areas (Owino et al., 2011).
Therefore, special attention should be given to conserve not only the Grants
gazelles but also other wildlife in the area. Frequent patrols of the Park should
be conducted to curtail human disturbances and funds must be allocated to relocate
people that live in the Park. The Park should focus on prevention/banning of
cutting trees rather than collecting charcoal from farmers.
We sincerely thank the Ethiopian Wildlife Conservation Authority for allowing
us to conduct this study in Abijata-Shalla Lakes National Park. We are indebted
to Addis Ababa University for providing funding.
Altmann, J., 1974. Observational study of behavior: Sampling methods. Behaviour, 49: 227-267.
Arctander, P., P.W. Kat, R.A. Aman and H.R. Siegismund, 1996. Extreme genetic differences among populations of Grant`s gazelle (Gazella granti) in Kenya. Heredity, 76: 465-475.
Ayenew, T., 2001. Numerical ground water flow modeling of the central main Ethiopian Rift Valley Lakes Basin. SINET: Eth. J. Sci., 24: 167-169.
Belovsky, G.E. and J.B. Slade, 1986. Time budget of grassland herbivores: Body size similarities. Oecologia, 70: 53-62.
Bergerud, A.T., 1971. The population dynamics of newfoundland caribou. Wildl. Monog., 25: 1-55.
Direct Link |
Birdlife International, 2009. Important Bird Area Fact Sheet: Abijatta-Shalla Lakes National Park, Ethiopia. Available on http://www.birdlife.org Accessed on 09/11/2009
CPI, 2000. Spectrum Guide to Ethiopia, 3rd Edn., Camerapix Publishers International, Nairobi, pp:163.
Caughley, G. and A.R.E. Sinclair, 1994. Wildlife Ecology and Management. 5th Edn., Blackwell Science, Massachussets, Pages: 334.
De Paul, O.V. and E. De Clercq, 2009. Factors influencing impala distribution patterns in Nairobi National Park, Kenya. Nature Preceedings 22 September 2009.
Dunham, K.M., 2001. Status of a reintroduced population of mountain gazelles (Gazella gazella) in central Arebia: Management lessons from an aridland reintroduction. Oryx, 2: 111-120.
Edwards, S., 1996. Important Bird Areas of Ethiopia: A First Inventory. Ethiopian Wildlife and Natural History Society, Addis Ababa, Pages: 300.
Estes, R.D., 1967. The comparative behavior of Grant's and Thomson's gazelles. J. Mamm., 48: 189-209.
Direct Link |
Estes, R.D., 1991. The Behavior Guide to African Mammals: Including Hoofed Mammals, Carnivores and Primates. University of California Press, Berkeley, pp: 611.
Fitzgibbon, C.D., 1990. Why do hunting cheetahs prefer male gazelles? Anim. Behav., 40: 837-845.
Direct Link |
Gerard, J.F., E. Bideau, M.L. Maublanc, P. Loisel and C. Marchal, 2002. Herd size in large herbivores: Encoded in the individual or emergent? Biol. Bull., 202: 275-282.
Direct Link |
Gobena, A., 2008. Assessment of ecotourism potentials for sustainable natural resources management in and around Abijata-Shala Lakes National Park in the central Ethiopian Rift Valley. M.Sc. Thesis, Addis Ababa University.
Grier, J. and T. Burk, 1992. Biology of Animal Behavior. Mosby Year Book Inc. St. Louis, Boston, pp: 392.
Hart, B.L., 1992. Behavioral adaptations to parasitism: An ethological approach. J. Paras., 78: 256-265.
Direct Link |
Hartley, P.H.T., 1953. An ecological study of the feeding habit of English titmice. J. Anim. Ecol., 22: 261-288.
Direct Link |
Hillman, J.C. and S.M. Hillman, 1987. The mountain nyala (Tragelaphus buxtoni) and simien fox (Canis simensis) in the Bale mountains national park. Walia, 10: 3-6.
Hillman, J.C., 1993. Ethiopia: Compendium of Wildlife Conservation Information (CWCI). Vol. 1, Ethiopia Wildlife Conservation Organization, Addis Ababa, pp: 27.
Kilonzo, J.M., W.N. Ekaya and R.N. Kinuthia, 2005. Feeding characteristics of sheep (Ovis aries ) and Grant`s gazelles (Gazella granti) on Kapiti ranch, Kenya. Afr. J. Ran. For. Sci., 22: 1-10.
Direct Link |
Kingdon, J., 1997. The Kingdon Field Guide to African Mammals. Academic Press, London, UK., pp: 476.
Knight, R.R., 1970. The Sun River Elk herd. Wildl. Monogr., 23: 1-6.
Lewis, J.G. and R.T. Wilson, 1979. The ecology of Swayne`s hartebeest. Biol. Conserv., 15: 1-12.
Direct Link |
Nowak, R.M., 1991. Walker`s Mammals of the World, Baltimore. John Hopkins University Press, Maryland, pp: 1629..
Oindo, B.O., 2002. Body size and measurement of species diversity in large grazing mammals. Afr. J. Ecol., 40: 267-275.
Okello, M., 2005. An Assessment of the large mammal component of the proposed wildlife sanctuary site in Masai KuKu Group Ranch near Amboseli, Kenya. S. Afr. J. Wildl. Res., 35: 63-76.
Olff, H., M.E. Ritchie and H.H.T. Prins, 2002. Global environmental determinants of diversity in large herbivores. Nature, 415: 901-905.
Owino, A.O., M.L. Kenana, P. Webala, S. Andanje and P.O. Omondi, 2011. Patterns of variation of herbivoure assemblages at Nairobi National Park, Kenya, 1990-2008. J. Envir. Protec., 2: 855-866.
Direct Link |
Prins, H.H.T., 1992. The pastoral road to extinction: Competition between wildlife and traditional pastoralism in East Africa. Envir. Conserv., 19: 117-123.
Qiao, J., W. Yang, W. Xu, C. Xia, W. Liu and D. Blank, 2011. Social structure of Goitred gazelles Gazella subgutturosa in Xinjiang, China. Pak. J. Zool., 43: 769-775.
Direct Link |
Raman, T.R.S., 1997. Factors influencing seasonal and monthly changes in the group size of chital or axis deer in southern India. J. Bio. Sci., 22: 203-218.
Direct Link |
Shorrocks, B. and A. Cokayne, 2005. Vigilance and group size in impala (Aepyceros melampus Lichtenstein): A study in Nairobi National Park, Kenya. Afr. J. Ecol., 43: 91-96.
Spinage, C.A., C. Ryan and M. Shedd, 1980. Food selection by the Grant's gazelle. Afr. J. Ecol., 18: 19-25.
Stark, M.A., 1986. Daily movement, grazing activity and diet of Savanna buffalo, Syncerus caffer brachyceros, in Benoue National Park, Cameroon. Afr. J. Ecol., 24: 258-266.
Stelfox, J.B., R.J. Hudson and N. Groer, 1984. Relationships among physical traits, age and social status in Thomson's and Grant's gazelles. Anim. Behav. Sci., 13: 347-357.
Stuart, C. and T. Stuart, 1997. Field Guide to the Larger Mammals of Africa. Struik Publishers, Cape Town, pp: 144.
Sutherland, W.J., 1996. Ecological Census Technique: A Hand Book. Cambridge University Press, London, pp: 336.
Sutherland, W.J., I. Newton and R.E. Green, 2005. Bird Ecology and Conservation. A handbook of techniques, Oxford University Press, Oxford, pp: 386.
Tefera, F. and R. Almaw, 2002. Conservation and Management Issue of Abijata-Shalla Lakes National Park. Oromia Natural Resource Conservation and Environmental Protection Authority, Addis Ababa, pp: 32.
Walther, F.R., 1972. Social grouping in Grant's gazelle (Gazella granti Brooke 1827) in the Serengeti National Park. Zeitsc. fur Tierpsy., 31: 348-403.
CrossRef | PubMed |
Walther, F.R., 1991. On herding behavior. App. Anim. Behav. Sci., 29: 5-13.
Wilson, D.E., F.R. Cole, J.D. Nichols, R. Rudran and M. Foster, 1996. Measuring and Monitoring Biological Diversity: Standard Methods for Mammals. Smithsonian Institution Press, Washington D.C., pp: 409.
Woie, B.M., 1984. Influence of frequency and intensity of clipping on forage yield, crude protein content and digestibility of six Kenyan range grasses. Ph.D. Thesis, Texas A and M University, USA.