Table 7: here
4. DISCUSSION
A total of 131 species of birds were recorded from the southern gulf of
Lake Tana and its adjacent habitats, which indicates that the area is
rich in its avian diversity. Majority of the avian species belong to the
order Passeriformes. This result agrees with the findings of Esayas
(2011) and Genet & Ejigu (2017) as they confirmed that order
Passeriformes is also the most diversified species in other parts of the
country. The distribution of birds in the different habitat types within
the study site varied among each other. The highest number of avian
species was recorded in the Debremariam wetland during the wet season.
This might be due to the availability of high vegetation complexity and
floristic composition of the wetland habitats as the swampy habitat
holds papyrus (Cyperus papyrus ) and Typha plants, which are
important for feeding, nesting, and breeding sites for wetland birds. In
addition to this the large size of Debremariam wetland as it compared to
the other two sites might contribute to the highest avian species
diversity. This is because of the availability of multiple and varieties
of alternative food sources for different avian species. The lowest
number of avian species recorded in the adjacent areas of Lake Tana
might be due to food scarcity. Telleria & Santos, (1994) described that
habitat structure affects the distribution of individual species.
Moreover, habitat size (Willis, 1979), modes of foraging (Marone, 1991),
and floristic composition (Wiens & Rotenberry, 1981) have significant
influence on the abundance and distribution of species in an area.
Season is one important factor that determines avian species composition
and abundance in the area. During the dry season, relatively a greater
number of avian species is found at the head of the Blue Nile River.
This is because many birds from Debremariam wetland locally migrate to
this site as the wetland is dried out during the dry season. Debremariam
wetland consists of more open land and swampy habitats compared to head
of the Blue Nile River, and during the dry season over half of these
areas are changed to dryland and most are used for cattle grazing
ground. The distinct seasonality of rainfall and seasonal variation in
the abundance of food resources result in seasonal changes in the
species abundance of birds (Gaston et al., 2000; Molla, Ejigu &
Yitayih, 2021). The distribution and abundance of many avian species are
determined by vegetation composition that forms a major element of their
habitats. As vegetation changes along complex geographical and
environmental gradients, a particular bird species may increase or
decrease in number and disappear as the habitat changes (Lee &
Rotenberry, 2005).
Wide areas of wetlands are being converted into farmlands and urban
expansion that affect many bird species (Meyer & Turner, 1992). In
addition to this, habitat fragmentation could affect distribution and
abundance of birds by influencing habitat use, reproduction and
survival. The removal of emergent vegetation could also affect birds
that use the vegetation as food source (Rodewald & Yahner, 2001).
People residing at the adjacent areas of Lake Tana and Debremariam
wetland use the matured papyrus for local boat construction, and it is
also used to spread at home during coffee ceremonies, which contribute
for destruction of avian habitats and could affect their abundance and
diversity in the area.
The distribution and abundance of birds could be affected in similar
ways by the degree of specialization in their ecological requirements
(Cofre et al., 2007). In the present study, egrets (B.
ibis), Egyptian geese (A. aegyptiaca ), hammerkops
(S. umbretta ), sacred ibis (T. aethiopicus ), African
jacanas (A. africanus ), herons (Ardeidae ), and
darter (A. rufa) prefer wetlands and water bodies. Common bulbul
(P. barbatus ), eastern grey plantain eater (C. zonurus ),
and greater blue eared starling (L. chalybaeus ) mainly prefer
forest habitats, while wagtails (Motacillidae) and fiscals
(L. collaris ) prefer open land habitats. All habitats have
certain particulars to attract birds of great ecological importance
(Manhals & Ribeiro, 2005).
Herons, egrets, ibis, and jacana feed in shallow waters to catch diverse
aquatic animals including fish, amphibians, and aquatic invertebrates.
They prefer open and shallow areas as these habitats are rich in
resources. They avoid the dense vegetation habitats that interferes with
their movement and foraging efficiency (White, 2003; Lantz et al.,
2011). When the water level increases, they moved to other areas as
shallow water prey is easier to catch compared to deep water habitats
(Liordos, 2010; Lantz et al., 2011). During the wet season, most birds
were not found in adjacent areas of the Lake because water level was
very high but after the wet season this area was very rich with
different avian species. The highest water bird species richness occurs
in the reed bed where water level is shallow (Holm & Clausen, 2006).
In the Debremariam wetland, there are many resident birds. In the back
yard of the local people, there are many fruits such as mango, banana,
lemon, coffee, and different types of vegetables that can attract many
avian species. Habitats which are dominated by patches of shrubs and
fruiting trees can attract a number of bird species (Knight et al.,
2001). The relative abundance of avian species from the three different
habitats showed that over half (58%) of the avian species identified
are uncommon species. Ryan & Owino (2006) suggested that the presence
of large number of uncommon species in a certain area could be related
to the breeding nature, large home range, and niche of the species.
Some of the most common species from Debremariam wetland and head of the
Blue Nile River are African jacana, laughing dove, red
billed fire finch, red checked cordon bleu, speckled pigeon, village
weaver and yellow billed egret. This might be due to the presence of
suitable habitat and weather condition in the area. The Sorensen’s
coefficient of adjacent area of Lake Tana and head of the Blue Nile
River showed that the overall community similarity of the two study
sites is very high. Moreover, the overall community similarity of
Debremariam wetland, adjacent areas of Lake Tan, and head of the Blue
Nile River is relatively higher. This indicates that avian community
composition of the three study habitats is similar. Tubelis &
Cavaicanti (2001) showed that similarity of avian species composition
between habitats indicates a tendency for similar habitats to have
similar species composition (Genet & Ejigu, 2017). In contrast, the
lowest avian species similarity was between adjacent area of Lake Tana
and Debremariam wetland. This might be due to the differences in feeding
adaptation of avian communities in each habitat types. Aich &
Mukhobabadhyay (2008) described that canopy closure supports more of
habitat specialist species, while areas under anthropogenic influence
harbored more of opportunistic species.
The highest species diversity occurred in Debremariam wetland during the
wet season compared to the other two habitat types. This could be due to
the presence of better food availability in the wetland. Less mean
species evenness is recorded at the head of the Blue Nile River during
the dry season, which indicates that there is an unbalanced distribution
of the number of individuals among different species. This uneven
distribution in avian species richness can partly be attributed to
differences in the habitat type and quality (Marie et al., 2008).
Most avian species are limited by availability of food. Seasonal
fluctuations in the abundance of individual species are more extreme.
During the dry season, some avian species totally left the area,
decreasing both in number of species and their abundance. This is
similar to the findings of Wiley et al. (1996 ), which confirm
that different habitat features affect the habitat selection of birds.
It is showed that the avian community structures in the marsh and water
bodies are influenced by a number of environmental factors including
water depth, vegetation structure and composition, food resource and
foraging behavior (Chimney & Gawlik, 2007). The availability of food
and human interference has great negative impact compared with the
impact of weather conditions in affecting the activity of birds.
However, avian species prefer sunny and warm days than cold weather
conditions.
5. CONCLUSION
The southern gulf of Lake Tana is a suitable habitat to support
different avian species. The present study confirmed that wetlands,
adjacent areas of the lake, and head of the Blue Nile River can support
more avian species belonging to different orders and families. Family
Ploceidae, Columbidae, Accipitridae, Ardeidea, Scolopacidae and
Motacillidae are the most widely distributed families in the area. One
endemic bird species of Ethiopia and one shared with Eritrea are
identified in the study area. Diversity and abundance of avian species
were relatively the highest at Debremariam wetland and it is followed by
head of the Blue Nile River and adjacent areas of Lake Tana. However,
wetlands are managed primarily for human land uses mainly for livestock
grazing and farming rather than for biodiversity conservation. Thus,
habitat disturbances due to various anthropogenic activities have
significant negative impact on the conservation of avifauna. As a
result, proper management strategies should be designed and implemented
in order to maintain the Lake’s ecosystem to ensure conservation of
avian species in the area.
ACKNOWLEDGEMENTS
We would like to acknowledge Dr. Ali Seid for borrowing us different
field equipment during data collection period and Dr. Melaku Wale in
assisting data analysis. The National Metrological Service Agency, Bahir
Dar Branch, is acknowledged for the provision of metrological data of
the study site. We owe thanks to Mrs Fentanesh Haile for her help in
preparing map of the study area. College of Science, Bahir Dar
University is acknowledged for the research fund provided to the first
Author.
CONFLICT OF INTEREST
The authors declare that there is no competing of interests.
AUTHOR CONTRIBUTIONS
Belaynesh Abebaw & Dessalegn Ejigu design the research proposal, and
Belaynesh Abebaw & Tilahun Kefyalew directly involved in data
collection. Dessalegn Ejigu & Ayalew Wondie participated in supervision
activities during field data collection time. All of us contributed
during data analysis mainly Belaynesh took the lead, and Dessalegn Ejigu
prepared the manuscript in which all the authors edited and approved the
final version before its submission.
DATA AVAILABILITY STATEMENT
All data used are included in the article.
ORCID
Dessalegn Ejigu: https://orcid.org/0000-0002-5672-4484
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