Population Ecology of Menelik's Bushbuck

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Festuca abyssinica Hochst. b,c. 4 yl,ml. 0.8. Kentefa. Fabaceae. Pterolobium stellatum Brenan a. 2 yl. 0.2. Kentefa. Fabaceae. Entada abyssinica Steud. a. 2 yl.
International Journal of Ecology and Environmental Sciences 37 (1): 1-13, 2011 © NATIONAL INSTITUTE OF ECOLOGY, NEW DELHI

Population Ecology of Menelik’s Bushbuck (Tragelaphus scriptus meneliki, Neumann 1902) from Denkoro Forest Proposed National Park, Northern Ethiopia DEREJE YAZEZEW 1 , YOSEF MAMO 2 AND AFEWORK BEKELE 1 * Department of Biology, Addis Ababa University, PO Box 1176, Addis Ababa, Ethiopia 2 Hawassa University, PO Box 5, Hawassa, Ethiopia *Corresponding author; E-mail: [email protected]

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ABSTRACT Population status, structure, habitat association and feeding behaviour of Menelik’s Bushbuck (Tragelaphus scriptus meneliki) were studied in Denkoro Forest Proposed National Park, Ethiopia from August 2008 to M arch 2009. Transect and silent detection methods were employed for population assessment. A total of 230 individuals was estimated with a population density of 11.75 km-2 . The population was female biased. Male to female ratio was 1.0:1.5 and the ratio of young to female was 1.0:7.5. The age structure was 59.26% adult, 33.33% sub-adult and 7.41% young. Group size varied within seasons. They were highly associated to forest habitat and more distributed in the Erica woodland than the Festuca grassland. M enelik’s Bushbuck consumed 46 plant species which consisted of 19 herbs, 13 shrub, 12 trees and two lianas. Leaves and young shoots comprised the largest proportion of the food items consumed. Peak activities were observed early morning and late afternoon hours with resting peak during the mid-day. Key W ords: Activities, Denkoro Forest, Food Items, Habitat Association, Population Status.

INTRODUCTION Ethiopia is a country of great geographical diversity with high and rugged mountains, flat-topped plateau and deep gorges, incised river valleys and rolling plains. The country is endowed with extensive and unique environmental conditions, ranging from Dallol (100 m below sea level) at Kobar in Afar depression to Ras Dejen (4620 m above sea level) (Yalden 1983). The altitudinal variation within Ethiopia produces a range of climate, which affects the distribution of fauna and flora (Yalden and Largen 1992). This is mainly reflected by altitudinal ranges and diversity of climate, vegetation and landscape. Ethiopia possesses a unique and characteristic fauna with a high level of endemism (Hillman 1993, Tedla 1995). Out of the 284 mammalian species so far recorded from Ethiopia, 31(11%) are endemic (Hillman 1993, Abune 2000). Many of these endemic animals are specifically associated with the high altitude moorland and grassland habitats. Others

belong to the highland forests while a few occur within the lowland forests of southwest Ethiopia. Out of the documented 31 endemic mammals of the country, 17 are highland altitude moorland or grassland species whose altitudinal range is confined to above 2000 m asl. One of these endemic mammal species is the Menelik’s bushbuck, which is the species of the present study. The endemic Menelik’s bushbuck is confined to the highland forests of Bale, Menagesha Suba State Forest and other highland areas. Most authors consider Menelik’s bushbuck as a montane form distinguished by long hair, absence of pale dorsal markings and a very dark greybrown pelage in the male. Females are reddish in colour, hornless and much smaller than males (Yalden et al. 1984). Throughout historical times, Menelik’s bushbuck has occupied a limited and disjunct range in the Chercher, Arsi and Bale Mountains, the mountains of western Shoa and areas of high ground in the province of Illubabor (Yalden et al. 1984). Menelik’s bushbuck is one of the ungulate mammals that also occurs in the

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Denkoro Forest Proposed National Park (EWNHS 1996). Over forty races of bushbucks have been identified in Africa, which vary both in coloration and the type of habitats they frequent. However, Yalden et al. (1984) suggested that the extraordinary variability of bushbuck accounts for the large number of names incorporated in the literature. Bushbucks consist of two genetically divergent lineages. One lineage inhabits the northwestern half of the African continent (T. s. scriptus) and the other lineage inhabits the southern-eastern half (T. s. sylvaticus). Bushbucks (both common and Menelik) have not been the subject of research studies in Ethiopia. As a result, little is known about the habitat requirements, food preferences and behaviour of this ungulate in the country. The most plausible explanation why bushbuck has been so little investigated is its cryptic lifestyle (Wronski et al. 2008). Moreover, Menelik’s bushbuck is relatively difficult to observe, as it mainly inhabits dense habitat with sufficient cover and adequate forage, similar to the other subspecies, the common bushbuck (MacLeod et al. 1996, Kingdon 1997, Apio and Wronski 2005, Wronski et al. 2006b). The present study is an attempt to investigate the ecology of this little known subspecies endemic to Ethiopia.

THE STUDY AREA The present study was carried out in Denkoro Forest Proposed National Park (DFPNP), which is located in south Wollo Zonal Administration of Amhara Region, Ethiopia, situated between 10o 47’-10o 50’N latitude and 38o 35’-38o 42’E longitude, about 600 km north of Addis Ababa (Figure 1). The altitude ranges from 2,300 to 3,665 m above sea level. The area is generally characterized by rough topography, deeply incised valleys, escarpments and plateaux (Ayalew et al. 2006). Previously, the forest covered an area of 5,500 ha. However, this forest has been reduced due to deforestation and encroachment by the local people. The annual pattern of rainfall in the area is bimodal with a long rain season during June to September and a short rainy season during March to April. The mean annual rainfall is 845 mm, ranging from 655 to 1,165 mm. The lowest temperature recorded during the wet season was 7.4o C in August and the highest during the dry season was 26.4o C in February. The dense forest covers 19.6 km2 while the rest of the reserve lies in the

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cold part of the Afro-alpine zone, which covers 35.4 km2 of the proposed National Park. Between 2,400-3,000 m, the area comprises a thick forest. Above 3,000 m, the Erica woodland gradually changes to Festuca dominated Afro-alpine grassland with some scattered giant Lobelia (EWNHS 1996). Geologically, the area lies on extremely thick Tertiary volcanic deposits with soils comprising mainly of Lithosols. Denkoro River, which flows to the west to join the Nile River, is one of the permanent sources of water in the area. In addition to Menelik’s bushbuck, preliminary survey revealed the presence of 22 large and medium sized mammals in the area. The residents in the study area are engaged in agriculture. To a large extent, most human settlements are concentrated along the periphery of the forest surrounded by agricultural land. Thus it is not uncommon to encounter bushbucks in the village during night. Cattle are reared mainly for ploughing, traction and milk production.

METHODS A reconnaissance survey was conducted on foot during the first two weeks of August 2008. During this period, information regarding accessibility, climatic conditions, vegetation types, fauna, topography, infrastructure, water sources, and bushbuck occupancy and distribution in the area was gathered. Knowledge and experience of the local people were used to identify the habitat types and to locate the sampling sites. Three habitats used by bushbuck were identified: forest habitat, Erica woodland and Festuca grassland with Lobelia. Farmland habitat was ignored as the animals were not observed during the day time in this area. Data collection was carried out from August 2008 to March 2009 to cover wet and dry seasons. Quantitative data were obtained on the population size and structure, group size, distribution and habitat association from transect counts; as well as diurnal activity patterns with special reference to feeding behaviour of bushbuck during the study period. Moreover, sighting distance and sighting angle of the animal/herd from the observer were recorded. Sample sites/census zones were taken from different habitats, which have sloping areas, dense forests, grasslands, woodlands, bushlands and thickets under the three habitat types. Sample sites were census zones where transects were established. Five sample sites were randomly selected for the forest habitat and one sample

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Figure 1. Map of the study area with the habitat types and census zones.

site for each of the Erica woodland and Festuca grassland with Lobelia habitat types. A total of 23 transects were considered in all the three habitat types; 17 for the forest habitat and three for each of the Erica woodland and Festuca grassland. Seventeen transects were assigned to five sample sites for the forest habitat types, four transects for each of Gishewa and Sekedereba but three transects for each of Bukie, Gurtou and Harro. The number of transects among sample sites varied depending upon visibility (Norton-Griffiths 1978, Ndhlovu and Balakrishnan 1991) and the length of transects varied from 1.5 to 3.0 km. Transect width ranged from 20 m to 100 m depending on visibility of the animal associated with vegetation cover and topography of the sample site. There was a distance of

300 m between two adjacent transects to avoid double counting. Starting points of each of the transects were marked with permanent coloured markers. This was made at 100-200 m interval along transects during the first survey, following the method used by Ndhlovu and Balakrishnan (1991) to avoid confusion during transect walking. In addition, transect lines were also demarcated by poles and/or natural markings such as streams, rivers, big trees and rocks. The sampling unit selected from each census zone represented 20-25% representative samples of the study area. Line-transect method was used to obtain data on population status, group size, and structure of Menelik’s bushbuck in the study area (Norton-Griffiths 1978, Buckland et al. 1993, Sutherland 1996, Wilson et al.

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1996). Line-transect sampling was designed based on straight lines to yield sufficient information to conduct proper statistical analysis and to avoid systematic error or bias (Anderson et al. 1978). Transects were surveyed with the help of experienced scouts. Census was carried out from 06:00 - 10:00 h in the morning and 14:00 18:00 h in the afternoon, when the animals were most active and visibility was good (Dankwa-Wiredu and Euler 2002, Wronski et al. 2006a). In some instances (early morning and late afternoon), transects were walked in a direction opposite to sun rays to minimize light rays to the observer and maximize observation. Surveys were made equally throughout the wet and dry seasons and in all sites during the day time to assess the current population status. The movement of the observer was followed against the direction of the wind in order to minimize smell by the animals, and noise was minimized to avoid disturbance of individuals. A total of four counts were made during the wet and dry seasons. Transects were walked systematically with slow pace (1 km/h) to maximize the probability of observing all individuals (Norton-Griffiths 1978). Information on group size, group composition, and structure was recorded once a month in each habitat type before the commencement of focal studies (Kivai et al. 2007). Bushnell binoculars were used for sex and age identification. Starting time, stop, and change of habitat were recorded. Group size, sex, age structure, time of observation, as well as the sighting distance and sighting angle of the animals were recorded in each of the transects. These were calculated by the Distance software programme. The population estimate of Menelik’s bushbuck was obtained by multiplying the population density with the total area of suitable habitat inhabited by the animals. The population density is the number of counted individuals divided by the area of the strip (Norton-Griffiths 1978, Wilson et al. 1996). From these data, population density was calculated by the formula:

where, g(y) is the probability of detection at distance y and w is the truncation distance. Effective strip width can therefore be calculated by numerical integration of g(y). Age and sex composition of Menelik’s bushbuck were recorded during the wet and dry season census periods. During counting, each of the individuals was grouped into its respective age and sex categories. The categories used were young, sub-adult and adult. Sex and age determination were made based on body size and shape, presence or absence of horns, horn size and shape, and coat colour. Information on the demographic composition was used to forecast the population trend of Menelik’s bushbucks. During each observation, the size of the group of Menelik’s bushbuck was recorded before treating the group into its respective age and sex categories. Solitary individuals were considered as a group of one for statistical purposes (Arcese et al. 1995, Sorensen and Taylor 1995). Groups were considered as solitary individuals or collections of individuals that moved together. Individuals were considered as a member of the same group if the distance between them was less than 50 m (Refera and Bekele 2004). Habitat association and distribution of Menelik’s bushbuck in the study area was determined from the data obtained from the transect count during wet and dry seasons. During the census, the type of habitat where the animals were observed was recorded for each season. The size of herds observed in different habitat types during the wet and dry seasons was used to compare the habitat preference of these animals following the method of Norton-Griffiths (1978). Habitat association of Menelik’s bushbuck was determined from the relative frequencies of observation of the animals in each habitat. All the data gathered were used to determine the habitat association and distribution of the animals.

D = n/2LxSW, where D=population density, n=number of sightings (number of animals seen), L=transect length and SW= strip width. All sightings were pooled together to find out the overall density estimate for the whole study area. Strip width is given by the formula:

Following the methods used by Brashares and Arcese (2002), detailed behavioural activities were made on recording sheets. Direct observation was made on the behaviour of a focal animal engaged in different activities. Focal animals were followed and data on their diurnal activities were recorded every 15 minutes with five minutes sampling gap between 06:00-18:00 h (fixed interval time point sampling) following the method of Altman (1974), and Martin and Bateson (1985). Focal animal was followed at a distance between 20-200 m and

ACTIVITY PATTERNS

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observed using binoculars and/or naked eye depending on the distance between the observer and focal animal as well as the topography of the habitat. To facilitate observation, strategic sites such as hilly terrain were chosen. Sightings were carried out by selecting suitable vantage points, which provide a broader view than low landscape positions. If the focal animal in the field disappears from vision, the time interval of its disappearance and reappearance was recorded. When the animal remained away for longer than the duration of common activities, it was cancelled from the sample and then duration of the sample period was reduced accordingly. Observation was made for five consecutive days for each study period. A total of 20 days behavioural observation was used for the whole study period. At each sampling point, the major activities of a focal animal was recorded as feeding, moving, resting/lying, standing and other categories. Feeding habits were studied by examination of fresh feeding signs that is observed from suitable vantage points. The animal was observed from a strategic place while consuming a particular plant species. Immediately after the animals left the spotted area, plants consumed by Menelik’s bushbuck were identified and recorded or samples were collected, pressed and brought to the Addis Ababa University Herbarium for identification. Data were analyzed using SPSS software version 15.0. Population estimate of Menelik’s bushbuck during the wet and dry seasons was compared using Mann Whitney U test (P=0.05). Data were analyzed to estimate the population density of Menelik’s bushbuck using “DISTANCE” software programme Version 5.0 (Buckland et al. 1993). Sex structure and age category were compared using Mann-Whitney U-test. Group size, distribution and habitat association were also compared using Mann-Whitney U-test for independent samples. The differences in the amount of time spent for different activities at different seasons were also analyzed using Mann-Whitney U-test. Descriptive analysis of feeding time, plant species and plant parts consumed by Menelik’s bushbuck was used to identify the feeding behaviour of the species.

RESULTS A total of 43 and 38 individuals of Menelik’s Bushbucks were recorded during the wet and dry seasons, respectively (Table 1). The total population estimate for wet and dry seasons was 239 and 222 individuals,

respectively. Among the different sites sampled during the study period, the highest sample count was in the forest whereas the lowest (zero) was in Festuca grassland habitats (Table 2). Mann-Whitney U-test analysis of the population size of Menelik’s bushbuck revealed that there was no significant statistical difference between wet and dry seasons (P> 0.05).

Table 1 Population estimates of Menelik’s bushbuck based on sample counts (Mean ± SE) . Season

Individuals Observed

Population Density km-2

Population Estimate

Wet Dry Mean

43±4 38±3 40.5±2.5

12.17± 4.09 11.32± 3.16 11.75± 2.52

238.53±85.89 221.87±66.36 230.30±52.92

Table 2 Number of individuals of Menelik’s bushbuck observed at each sample site in different habitats

Habitat types Forest Bukie Gishewa Gurtou Sekedereba Harro Erica woodland Grassland Total

No. of transects

3 4 3 4 3 3 3 23

Wet

Dry

6 9 6 9 5 3 0 38

8 7 7 11 7 3 0 43

Mean

7 8 6.5 10 6 3 0 40.5

Out of the average 40.5 individuals of Menelik’s bushbuck sighted during the observation period, 38 were adults and sub-adults and the others were young (Table 3). Furthermore, on the average, 59.26% of the individuals observed were adults, 33.33% sub-adults and 7.41% young. During the study period, more adult individuals were counted than sub-adults and young ones. Among the populations of Menelik’s bushbuck sighted in DFPNP, females on average constituted 55.55% and males 37.04%. However, Mann-Whitney Utest analysis of the sex structure showed that this was not statistically significant (P>0.05). Mann-Whitney U-test

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analysis of the age structure showed that there was no significant statistical difference in the age distribution during the wet and dry seasons (P> 0.05).

Table 3 Sex and age structure (Number of individuals; mean± SE) of Menelik’s bushbuck population during wet and dry seasons

Categories

Wet Season

Dry Season

Adult males Adult females Sub-adult males Sub-adult females Young Ratios Male: Female Sub-adult: Adult Young: Others Young: Females

11±1 16±3 5±1 8±1 3±2

8±1 13±2 6±2 8±1 3±1

9.5±1.5 14.5±1.5 5.5±0.5 8±0.0 3±0.0

1:1.50 1:2.08 1:13.33 1:8.00

1:1.50 1:1.50 1:11.67 1:7.00

1:1.50 1:1.78 1:12.50 1:7.50

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Table 4 Group size of Menelik’s bushbuck observed during wet and dry seasons (Mean ± SE)

Season

Individuals observed

Wet Dry Mean

43 38 40.5

Number of group/Cluster 27±2.0 28±3.0 27.5±2.5

Group size Range Mean 1-3 1-2 1-2.5

1.59±0.11 1.43±0.95 1.51±0.53

Mean

The total number of groups, group size and mean group size of Menelik’s bushbuck based on sample counts during the wet and dry seasons is shown in Table 4. The minimum and maximum group size recorded was one and three individuals, respectively. The mean group size was 1.59±0.11 during the wet season and 1.43±0.95 during the dry season. The average group size in the study area was 1.51±0.53. Mann Whitney U test showed that, there was no significant difference in the number of groups observed in the study area across seasons (P > 0.05). However, there was significant statistical difference observed in the mean group size in the study area during the wet and dry seasons (P< 0.05). The highest range of group size was recorded during the wet season, whereas the minimum group size was noted throughout the study period. Menelik’s bushbucks were observed in the dense vegetation (72.73%), where both food and cover were available more often than in the Erica woodland (27.27%). None of them were observed in the Festuca grassland habitat. Use of habitat types by Menelik’s bushbuck did not vary with seasons. MannWhitney U test showed that, the number of individuals observed in the two habitats was statistically different (P0.05) observed between wet and dry seasons in the habitat association of Menelik’s bushbucks.

A total of 2943 activity records were made. Menelik’s bushbucks were active (feeding and moving) for 60% and passive (lying and standing) for 30% of their day time and the rest 10% was spent for other activities (grooming, ruminating, socializing, defecation, object horning, watching, barking, reproductive activity and aggression). The percentages of time spent observed for various activities at different time of the day by Menelik’s bushbuck are given in Figure 2. Feeding showed two peaks, one in the early morning between 06:00 and 10:30 h and the other in the late afternoon between 16:00 and 18:00 h. Bushbucks commence feeding at about 06:00 h, if it is not raining. The interruption time is shorter during cloudy days than sunny days. Although feeding took place at all hours of the day until dusk, drastic reduction in feeding intensity was observed between 11:00 and 14:00 h. The average proportion of animals engaged in feeding activity for the whole day was 48.0%. Menelik’s bushbucks on average spent more time feeding (50.7 ± 4.38%) during the wet season than the dry season (45.3±2.83%). There was a significant statistical difference between seasonal feeding patterns (P< 0.05). Resting was frequent during the hottest parts of the day between 10:30 and 14:00 h (Figure 2). During this time, the number of animals involved in different activities was comparatively low as most animals move into thickets to hide themselves from the overhead sun radiation. Bushbucks on average spent 18.8±0.99% of their daily time during the wet season and 22±1.98 % during the dry season resting. Mann-Whitney U-test showed that there was a significant seasonal difference in resting between seasons (P< 0.05). Females often trigger the moving activity when they are in groups and all members withdraw to thickets or woodlands or run away and hide themselves for a while when they are disturbed. The amount of daily time spent

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Figure 2. Diurnal activity patterns of Menelik’s bushbuck

in moving is 11.84±1.77%. Bushbucks on average spend in moving 10.6±0.99% time during the wet season and 13.1± 3.25% during the dry season. However, there is no significant seasonal difference in the moving activity (P> 0.05). Standing is frequent between 10:00 and 14:00 h, after feeding. Standing time spent was 9.8±1.49% during the wet season and 9.2±1.97% during the dry season. However, there was no significant difference observed in standing between seasons (P>0.05). Other activities are performed during 06:00 to 18:00 h sporadically while the animals were feeding, moving, standing and resting. Other activities such as, grooming, socializing, defecation, watching, reproduction and aggressive behaviour were mainly observed during the warm period of resting and standing periods. Barking, grooming and object-horning (twig rubbing and ground trashing) were observed at any time of the day. This activity was at its peak between 11:00 and 14:00 h during resting and between 17:00 and 18:00 h when the animals start withdrawing to the thicket. Mann-Whitney U-test showed that there was no significant seasonal statistical difference in the time spent in other activities (P> 0.05). A total of 876 feeding observations were recorded from scan sampling of Menelik’s bushbuck. The overall diet of Menelik’s bushbuck during the study period is

Figure 3. Percentage of feeding time devoted to different food items by Menelik’s bushbuck.

shown in Figure 3. Young leaves contributed to 50.7 ± 2.5% of the overall diet. Mature leaves and shoots were the second and third favoured food items that comprised 38.3±3.8 and 6.7±0.3 percent, respectively. Flowers and fruits were consumed rarely. There was a significant difference in time spent feeding on young leaves, stems, flowers and fruits (P0.05) between seasons in time spent feeding on mature leaves and shoots (Figure 4).

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Figure 4. Mean seasonal percentage contribution of food items consumed by Menelik’s bushbuck.

Figure 5. Percentage of the major eight plant species consumed by Menelik’s bushbuck during the study period.

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Table 5 List of plant species, parts consumed and percentage composition of the diet of Menelik’s bushbuck

Local Name

Family

Dergu/Derg Atat Telenj Telenj Tifie Serdo Tikur telenj Maget Chemekot Engicha Gaja Tikur Enchet Koshim Yewusha sar Agam Kega Ets Henok Bezez Yeferes zeng Balame Wulkifa Weira Shinet Kechemo Atquar Dedho Asta Yedaget sar Kentefa Kentefa Dega Senbelet Kombel Yekok sar Amija Embis Bar Embis Yazo-Hareg Ets sabek Chakima Nacha Anfar Kosso Yemider Kosso Koshishila

Acanthaceae Celastraceae Acanthaceae Amaranthaceae Oliniaceae Poaceae Acanthaceae Fabaceae Fabaceae Cyperaceae Poaceae Rosaceae Flacourtiaceae Poaceae Apocynaceae Rosaceae Acanthaceae Malvaceae Lamiaceae Poaceae Sterculiaceae Oleaceae Myricaceae Myrsinaceae Loganiaceae Ebenaceae Ericaceae Poaceae Fabaceae Fabaceae Poaceae Celastraceae Poaceae Hypericaceae Sapindaceae Anacardiaceae Ranunculaceae Cucurbitaceae Anacardiaceae Euphorbiaceae Loganiaceae Rosaceae Rosaceae Acanthaceae

Species

Hyposestes forskaolli R.Br. Maytenus arbutifolia Wilczek Asystasia gangetica Anders. Achyranthes aspera L. Olinia rochetiana Juss. Cynodon dactylon L. Barieria ventricosa Hochst. Trifolium temnense Fresen Trifolium rueppellianum Fressen Cyperus rigidifolius Steud. Andropogon gayanus Kunth Prunus africana Kalkm. Dovyalis abyssinica Warb. Pennisetum thunbergii Kunth Carissa edulis Wahl. Rosa abyssinica Lindley Dyschoriste radicans Nees Hibiscus aponeurus Sprague & Hutch. Leucas martinicensis R. Br. Andropogon abyssinicus Fresen Dombeya torrida P. Bamps Olea europaea ssp. cuspidata Cif. Myrica salicifolia A.R. Ch. Myrsine africana L. Nuxia congesta R.Br. Euclea racemosa Murr. Erica arborea L. Festuca abyssinica Hochst. Pterolobium stellatum Brenan Entada abyssinica Steud. Themeda trianda Forssk. Maytenus gracilipes Exell. Oplismenus compositus P. Beauv. Hypericum revolutum Vahl. Allophylus abyssinicus Radlk. Rhus retinorrhoea Oliv. Clematis hirsute Perr. & Guill Zehneria scabra Sond. Rhus natalensis Krauss Acalypha psilostachya Hochst. Buddleja polystachya Fresen. Hagenia abyssinica Gmel. Alchemila pedata A. Rich. Acanthus sennii Chiov.

Habitat Types

Life forms

Parts consumed

a a,b a a a a a a a a,b a a a a a,b a a a a a a a a a a a b b,c a a a a, a,b a a a a a a a a a a a

3 1 4 4 1 4 4 4 4 4 4 1 2 4 2 2 4 2 4 4 1 1 1 1 1 2 2 4 2 2 4 2 4 2 1 1 5 5 1 3 1 1 4 2

yl, ml,st,sh,fl yl,ml,sh yl, ml,st,sh,fl yl,ml,sh yl,sh yl,ml,st yl,ml,sh yl,ml,st,sh,fl yl,ml,st,sh,fl yl,ml yl,ml yl yl yl,ml, yl,fr yl,ml yl,ml,sh yl,ml yl,ml yl,ml yl yl yl yl yl,sh yl yl,sh yl,ml yl yl yl,ml, sh yl,sh yl,ml,st yl,sh yl yl yl yl yl yl,ml,sh yl,sh yl yl,ml,st,sh yl

Time spent (%) 39.7 7.3 8.6 7.3 6.1 5.5 2.4 3.3 2.2 3.7 2.1 0.4 0.3 2.2 0.3 0.1 0.5 0.4 0.7 0.6 0.2 0.1 0.1 0.2 0.2 0.2 0.2 0.8 0.2 0.3 0.5 0.2 0.8 0.2 0.1 0.1 0.2 0.1 0.1 0.1 0.3 0.1 0.7 0.1

1=tree, 2=shrub, 3=perennial woody herb, 4=annual non-woody herb, 5=lianas/climber; a=forest, b=Erica woodland, c=Festuca grassland; yl=young leaves, ml=mature leaves, st=stem, sh=shoot, fl=flower, fr=Fruit

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Food use in the study area was extremely diverse. A total of 71 plant species belonging to 27 families was consumed. Among these, 46 were observed during feeding records while the remaining 25 species (including crops) were only seen to be consumed outside feeding records, and were therefore not included in the analysis. Out of these species of plants, more than 75% were perennial woody herbs, annual non-woody herbs and shrubs and the rest were trees and lianas. The highest contribution of the diet is from the family Poaceae (15.2%), Acanthaceae (10.9%), Fabaceae and Rosaceae (8.7%, each). Accordingly, these four plant families contributed about 43.5% of the total diet of the animals. The percentage composition of the plant species in the diet of Menelik’s bushbuck and the food items consumed are presented in Table 5. The eight most consumed plants accounted over 81% of the overall diet of Menelik’s bushbuck. Based on the overall percentage contribution, Hypoestes forskaolli was the most consumed plant species which accounted for 49%. Asystasia gangeica ranked second (10.6%), whereas Maytenus arbutifolia ranked third (9%) (Figure 5).

DISCUSSION To date, detailed published information on the population status and other ecological aspects of common bushbuck and Menelik’s bushbuck in Ethiopia is lacking. Therefore, the different aspects of their ecology will be compared with other studies carried out on common bushbuck elsewhere in other African countries. The separation of the study period into wet and dry seasons was important to have a clear lookout on the influence of the seasonal variation on the population status, habitat association and feeding behaviour of the studied animals. Density estimate of Menelik’s bushbuck relied on number of animals counted, transect length, survey area, sighting distance and sighting angle (Buckland et al. 1993). The population estimates of Menelik’s bushbuck showed no significant variation between wet and dry seasons and the obtained number was low in the study area. The possible reason for the low sighting of the animal in the area might be due to their more freezing behaviour that made them less observable leading to underestimation during the census count. The number of young individuals counted during both seasons did not vary. This does not go in line with the findings of Allsopp (1971) which indicated that

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bushbucks are seasonal in their reproductive behaviour. However, it is difficult to discuss the population trend of Menelik’s bushbuck in the present study area as population census of the species has not been made for a continuous period. Knowledge of sex ratio and age distribution of individual mammals is crucial for the evaluation of the viability of the species, because these variables reflect the structure and dynamics of the population (Wilson et al. 1996). The protection and eventual survival of an animal species can be successful only when its population dynamics is well understood and its economic and other values are recognized. The seasonal variation of age and sex distribution was insignificant. The result of the present study revealed that the male to female sex ratio is unequal. Females were predominant in the populations of Menelik’s bushbuck, which indicates that bushbucks have a potential to increase in number. The plausible explanation for the variation in sex ratio may be largely due to the increased mortality of males because they are more prone to predation than females and less vigilant when engaged in social interactions or because their condition is poor due to permanent agonistic interactions with other males. Even if an equal sex ratio of animals at birth is assumed, there is an increased mortality in young male ungulates (Ndhlovu and Balakrishnan 1991). Their solitary nature towards forming small groups enhances the vulnerability of males towards predators (Dasmann and Mossman 1962). This is because males leave their mother after maturity while females remain to form a mother clan (Wronski et al. 2006c). The explanation for male mortality is that bachelor males are distributed often in less favourable habitat as the central core area is inhabited by territorial males (Wronski 2004, 2005). Moreover, illegal hunting by poachers mostly affects males further skewing the sex ratio. The average ratio of young to others (1:12.50) in the present study may show a declining trend of the animal as a result of low percentage of breeding females or higher percentage of young predation. The actual reason for the low proportion of young in the population is not well understood. However, the most plausible reason may be the young have a tendency to be kept hidden under bushes or long grasses for the first four months. Hence, they could have been underestimated during the survey (Allsopp 1971, Wronski 2004). Moreover, they may be susceptible to predators at this stage as they are unable to escape. Jarman (1974) described that ungulates living in open habitats generally form larger groups than those

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living in forest habitats. The same principle is applied in Menelik’s bushbuck in the present study. There was a significant difference in group size in different habitat types, as well as between wet and dry seasons as evidenced by the present study. A narrow range of group size was recorded during the whole study period in Menelik’s bushbuck. This supports the findings of Wronski et al. (2009), which confirmed that bushbucks are indeed a solitary species, as one individual “peer group” was the most frequent “group size” in both bachelor and spinster groups in all populations they examined. The variation in group size during the wet and dry seasons could be a result of changes in the abundance of resources required in different habitat types and the ambient weather conditions. During the wet season, the solar radiation is shielded by the cloud cover, hence the animals leave thicket and congregate in the open for foraging, but during the dry season, they prefer thicket clumps to be protected from the intensive solar radiation. The other possible reason may also be their tendency to avoid predation in small group size as there is no more cover during the dry season due to defoliation. This is because bushbucks mostly defend themselves by hiding in thickets rather than combating, although males defend themselves when they are exposed. The variation in group size during the wet and dry seasons may also be a result of seasonality in breeding. The first step in studying the relationship between the patterns of distribution and habitat association of an animal species in a particular area is to identify and measure the characteristics of the area. Distribution of wildlife population can be explained mainly in terms of water and food requirements (Mwangi and Western 1998). Habitat selection of animals based on the availability of water and food effects changes in their density in natural areas on a seasonal basis. Moreover, utilization of habitat is often determined by the availability of cover and food and the rich plant growth (Dankwa-Wiredu and Euler 2002). Counts of Menelik’s bushbuck showed significant differences between forest and Erica woodland habitat during wet and dry seasons. Large individual counts occurred in the forest habitat because this habitat provides food, breeding site and protection (cover) from predation and overheating. Any fluctuation observed in the number of individuals between the two habitat types is, therefore, an indicator of change in habitat association and level of use. Such patterns are greatly influenced by the quality and quantity of various resources in each habitat.

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According to Delany and Happold (1979), the activity patterns of animals are correlated to their daily mode of life. The activity patterns of Menelik’s bushbuck change in hourly and daily bases. This signifies that activity change varies in response to environmental factors, the most important of which is ambient weather conditions. The activity pattern of Menelik’s bushbuck in DFPNP during daylight hours is contrary to a number of studies (Elder and Elder 1971, Wronski et al. 2006a) on common bushbuck, but agrees with Jacobsen (1974) and Dankwa-Wiredu and Euler (2002). In DFPNP, bushbucks are cathemeral (active any time). Menelik’s bushbuck devoted more time to feeding than any other activities during both seasons. Feeding was observed to be lowest at midday. The possible reason may be the influence of temperature, which affects the turgidity of plants which in turn affect the plants’ palatability. Dankwa-Wiredu and Euler (2002) found that at a temperature under 30o C, foraging plants of bushbuck remained turgid. However, when the temperature exceeded 31o C, the plants became flaccid due to loss of water and probably less palatable. Resting is high during the midday as the activities are affected by temperature. This behaviour was significantly different between wet and dry seasons. Food varies in quality and quantity between seasons and habitats. In the present study, the variation forced bushbucks to utilize some food items in a relatively lower quantity during the dry season than the amount they take during the wet season and vice versa. Several authors have shown that it is important to assess the quantity and quality of the most and the least eaten plant species that makes the bulk of the diet of a herbivore (Ego et al. 2003). The availability of data on feeding behaviour is used to specify the proportion of the diet containing different food items. During the present study, 46 plant species were observed as a food source of Menelik’s bushbuck. This study showed that the number of plant species found in the diet of bushbuck in each season varied slightly. The diet of Menelik’s bushbuck observed during the study period comprised mainly herbs. This is in accordance with previous studies of Jacobsen (1974), Odendaal (1983) and Dankwa-Wiredu and Euler (2002) for the common bushbucks. The present observation shows that Menelik’s bushbucks are mixed feeders, which rely on browsing herbs, shrubs and ground level bushes and grazing on a variety of grass species. This is related to the findings of Wronski (2006b) for bushbuck and Hofmann (1989) and Owen-Smith (1992) for other

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ungulate species. Bushbucks spent more time feeding on herbaceous species and grasses and less time on shrubs and trees during the wet season. However, during the dry season, the amount of time spent feeding on shrubs and trees increased as the availability of grasses and annual herbs decreased. In the study carried out by Okiria (1980), common bushbucks exhibited a similar strategy by concentrating to feed on the available shrub species during the dry season. As the rainy season resumed, they widened their acceptance range to include a considerable amount of herb species. This adaptive feeding style most probably contributed to the pronounced seasonality in foraging behaviour. This corresponds with the bushbuck’s ability to utilize a wide range of plant species as already reported by several researchers (Okiria 1980, Odendaal 1983, MacLeod et al. 1996, Haschick and Kerley 1997). Although Apio and Wronski (2005) reported that common bushbucks did not consume grass at all, grass species like Pennisetum clandestium, Cyperus rigidifolius, Andropogon gayanus, Andropogon abyssinicus, and Pennisetum thunbergi contributed a considerable percentage of the bushbuck diet, particularly during the wet season as observed in the present study.

ACKNOWLEDGEMENTS We thank the Department of Biology, Addis Ababa University for logistic and financial support. Help provided by the local administrators and people during the investigation period is highly acknowledged.

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