Discussion
The study has revealed that the study area supports a viable population
of geladas, though isolated from other sub populations in south and
north wollo administrative zones. However, the area supports fewer sub
population of gelada (mean population size 229) as compared to other
ranges of gelada (Beehneret al. 2008, 4620 individuals SMNP; Adem 2009,
529 individuals ; Ayalew 2009, 914 individuals; Abu 2011, 338
individuals; Moges 2015, 1502 individuals, Abie and Bekele, 2017, 1608
individuals and Goshme and Yihune 2018, 435 individuals). This could be
attributed to the fact that the area is the smallest area as compared to
its other ranges and the habitat is characterized by ravine topography,
which opens in to farm lands in all directions and more drier and with
less habitat quality as compared to other ranges in comparison.
Furthermore, threats such as habitat destruction in search of the
mineral opal and deforestation, retaliatory kill against crop damage,
which are intense in the present area (DWANRDO, 2016) as compared to its
other ranges, could reduce the population size. However, the population
size is larger than the recent report from estern escarpments of Tigray
(Hawzien and Ganta-Afeshum districts) 105 individuals (Girmay and Dati,
2020). This could be due the fact that the range of species in Tigrai
are more drier and with poorer habitat quality.
Significantly higher population of gelada was recorded during the dry
season that the wet season unlike the populations of the species over
its some other ranges. For example, there was no significant seasonal
variations in populations of gelada in Gich, SMNP (Woldegeorgis, 2015),
Debrelibanos, central Ethiopia (Abie and Bekele, 2017), Wof washa,
central Ethiopia (Goshme and Yihune, 2018), eastern escarpments of
Tigray (Girmay and Dati, 2020). This is mainly attributed to the
reproductive and crop raiding behavior of the species and the weather
condition at the particular study area. Normally, geladas give birth
after wet seasons, during early dry season (Ejigu and Bekele, 2014).
This could increase the number of youngs in the following dry season
ultimately increasing the total population during the dry season. The
most plausible explanation comes from the fact that there is intense
agricultural encroachment in the surrounding habitat of the species in
the present study area and wet season is a crop growing season, geladas
were observed to widely involve in crop raiding behaviour during the wet
season. Gelada is identified as one of a crop raider primate over most
of its ranges (Yihune et al., 2009; Moges, 2015). The diet of geladas is
predominantly composed of grasses and rhizomes (Moges, 2015). However,
cereal crops may be taken as an alternative food source where
agriculture encroaches onto the habitat of the gelada (Yihune et al.,
2009). Due to crop raiding behavior during the wet season, farmers chase
away geladas from their habitats bordering farmlands in to nearby cliffs
using guard animal like dogs and stone at geladas to protect crop
damage, which could reduce the sighting of the animals during wet
season. During the dry season, crops are harvested and this enables
geladas to roam freely among all habitat types. Similarly, Kifle et al.
(2013), recorded fewer individuals of geladas during the wet season than
dry season in Wonchit valley and discussed that this could be attributed
to the fact that wet season is a cultivation season and hence, farmers
have to chase away geladas far away from cropland and most of their open
habitat types. Furthermore, the foggy weather conditions during wet
season as compared to a bright sunny day during the dry season could
reduce the sighting of the animals during the wet season. The study area
receives 75- 80% rainfall during the wet season (ENMA, 2017). This high
amount of rainfall and fog could affect the probability of detection of
individuals’ gelada in the study area. Hunter (2001), reported that
excessive rainfall causes stress among geladas population and geladas to
overcome this heavy rainfall they aggregate themselves in their cliff.
In addition, human disturbances like firewood collection, opal mining,
grass cutting and livestock encroachments were higher during the wet
season than the dry season in the study area. When farmlands were
covered by crops during wet season, livestock moved into the habitats of
geladas for the sake of better foraging opportunities. This introduces
disturbances and competition for forage sources that could reduce the
probability of detection of gelada individuals during wet season. During
the wet season, human disturbance and livestock encroachments are higher
than the dry season over most highlands of Ethiopia (Hassain, Asghar,
Frid & Nurberdief, 2008; Girma, Bekele & Graham, 2012). Furthermore,
other disturbances such as firewood collection, grass cutting and opal
extraction (Rondeau et al., 2010) are more frequent during the wet
season than the dry season. During the wet seasons, farmers are
relatively free from their routine farm activities and have time to get
engage in activities such as firewood collection, grass cutting and opal
extraction, which is peculiar only to the range of gelada under study.
Moreover, during the wet season there are no incomes from crops and
hence, they have to engage in any other economic activities to meet
household economic demand (DWANRDO, 2016). All these increase
disturbances during the wet season that reduce the sighting of the
animals during the wet season.
Understanding of sex and age composition of wild animal populations is
important for evaluating the viability of the species as these variables
reflect the structure and the dynamics of wild animal population (Wilson
et al., 1996). The male to female gelada sex ratio in the study area
revealed female biased ratio (the adult male to female ratio is 1:1.96).
The result is consistent with other studies (e.g. Woldegeoriges (2015)
(the adult male to female ratio is 1:3) at Gich area of the Simen
Mountain National Park, Abie and Bekele 2017 (the adult male to female
ratio is 1:3.57) at Deberelibanos highlands, central Ethiopia and Moges,
2019 (the adult male to female ratio is 1:4.1 in Arsi). The female
biased ratio is a characteristic of naturally growing population under
normal circumstances (Beehner et al., 2008). Secondly, the reduced
number of male geladas could be attributed to retaliatory killings
induced by the species involvement in intense crop raiding behavior and
presence of predators. Kifle et al. (2013), reported that the numbers of
males in Wonchit valley were small due to similar crop raiding behavior
and retaliatory killing. In addition, the natural predator caracal(Files carcal ) has been observed to be frequent over most of the
habitats of gelada. Caracal could potentially prey on adult and sub
adult males that usually behaviorally isolate them from the main groups
of gelada and roam freely. Similarly, Roberts and Dunbar (1991) reported
that the male, especially bachelors and sub adult male geladas are
always vulnerable to predators. However, the reduced number of females
as compared to above studies carried out elsewhere over the ranges of
geladas could indicate predicts reduced population growth and signal for
immediate conservation attention.
Unequal mean ratio of juveniles to other age class in the study area was
observed. The possible reason of the small proportion of juveniles in
the study area could be less availability of food resource (due to
anthropogenic activities) that limits reproduction in the study area as
discussed above. Dunbar (1987), discussed that food resource
availability negatively correlates with the birth rate of gelada
population. Furthermore, the presence of natural predators such as
common jackal in the study area could reduce the juvenile population.
Common jackals were seen frequently moving between habitat patches
looking for prays. Juveniles at this stage are vulnerable towards
predators. Furthermore, unproductive female geladas may exist in the
population that could reduce the population of juveniles. Dunbar (2002),
revealed that the existence of unproductive female gelada attributes to
the existence of the small number of juveniles in gelada populations.
The mean group size (11.5) of gelada at Kotu forest was higher than
Chenek, Simien Mountains National Park (10.5) (Ejigu and Bekele, 2014),
Wof Washa Forest (Goshme and Yihune, 2018), Borena Saynit National Park
(Kifle, 2018), and Guassa Community Conservation Area (8.9) (Mamo and
Wube, 2019). However, fewer average group size than Gich, SMNP (15.4)
(Woldegeorgis, 2015) and Arsi (14.9) (Moges, 2019). According to Ohsawa
and Dunbar (1984), mean group size in geladas is mainly dependent on the
social factors that are related to group congregation. Variations in
group size are the results of cost and benefits of group congregation
mainly associated food and predators availability (Majolo, Vizioli and
Schino, 2008; Ejigu and Bekele, 2014). Generally, larger groups benefit
from defending predators and smaller groups benefit from less competion
for food. The relatively higher mean group size of geladas in the
present study area is probably attributed to the risk of predation from
carnivores such as caracal that were observed to frequently prey on
geladas during the study period. On the other hand the higher group size
and band size during dry season than wet season could be due to crop
raiding behaviour during dry season. During dry season crop are
harvested and could congregate to feed on crops and crops residue,
specially during early dry season (Kifle et al., 2013). During the dry
season predation risk could be minimized due to absence of foggy
weather, presence of open habitat that increase vigilance. It has been
reported that group size increases during dy season as there will not be
partial restrictions (Beehner et al., 2008). However, the findings of
the study contradict with findings of other similar studies elsewhere
over the ranges of geladas that stated that the higher mean group size
occurred during wet season than dry season (e.g. Abie and Bekele 2017;
Goshme and Yihune 2018 ). This could be explained due to variations in
food availability, climatic conditions and level of threats among the
study areas and the above cited literatures.
The distribution pattern of Gelada in the study area was not uniform,
varied depending on the food and water availability. The highest number
of Gelada was recorded in the open grassland habitat while the least was
in plantation forest habitat. It is known that the diet of geladas
predominantly comprises grass species (Moges, 2019). As indicated in the
study area description grass species highly preferred by the geladas
such as Cynodon aethiopicus, Andropogone abyssinicus, Pennisetum
clandestinum (Moges, 2015) are commonly abundant in the grassland
habitat, while they are very scarce in plantation forest. Furthermore,
the grassland habitat also offers permeant source of water for the
geladas. The result is in line with other studies such as Dunbar (1992),
Abi and Bekele (2017) and Goshme and Yihune (2018). The grassland
habitat preference is attributed to the better availability food and
water sources and increased vigilance effect. The open nature of the
habitat enables gelada to take a measure to avoid predators by visual
communication. Studies over
different ranges of geladas concluded that open grassland is the most
preferred habitat of geladas. This is attributed to the fact that
grasses and rhizomes comprise the predominant diet of geladas (e.g.
Dunbar 1987, 92; Moges, 2015)