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
REFERENCES
Aich, A & Mukhopadhyay, S. K. (2008). Comparison of avifauna at the edge of contrasting forest patches in Western Ghat hills of India.Ring, 30(1), 5-14.
Airinatwe, J. (1999). Wetlands and water bird conservation in East Africa: strategy for conserving migratory birds. Wetland International Publication , No55, Wageningen.
Aynalem, S. (2013). Birds of Lake Tana Area, Ethiopia. A photographic Field Guide, pp.235.
Ayenalem, S. & Bekele, A. (2009). Species composition, relative abundance and habitat association of the bird fauna of the montane forest of Zegie pensuela and nearby island Lake Tana, Ethiopia. SINET:Ethiopian Journal of Science, 32(1), 45-56.
Ayenalem, S. & Bekele, A. (2008). Species composition, relative abundance, and distribution of bird fauna of riverine and wetland habitats of Infranz and Yiganda at southern tip of Lake Tana, Ethiopia.Tropical Ecol ogy, 49, 199-209.
Barker, D.R. (2004). LakeNet: Lake Tana Symposium, Bahir Dar University, Bahir Dar Ethiopia.
Bibby, C.J. Jones, M. & Marsden, S. (1998). Expedition Field Techniques: Bird Surveys. ’e Expedition Advisory Center Royal Geographic Society, London, UK.
Bibby, C.J., Burgess, N.H & Hill, D.A. (2000). Bird Census Techniques. 2nd ed. Academic Press , London, pp. 302.
Buckland, S.T. (2006). Point-transect surveys for songbirds: Robust methodologies. Auk, 123, 345–357.
Chimney, M.J & Gawlik, D.E. (2007). The avifauna of constructed treatment wetland in South Florida used for Everglades’s restoration.Florida Field Naturalist, 31, 9-21.
Clout, M.N & Hay, J.R. (1989). The importance of birds as browsers, pollinators, and seed dispersers in New Zealand forests. New Zealand Journal of Ecol ology, 12, 27-33.
Cofre, H.L., Gaese, K.B & Marquet, P.A. (2007). Rarity in Chilean forest birds: which ecological and life-history traits matter.Diversity Disturb ution,13, 203-212.
Colwell, M.A & Taft, O.W. (2000). Water bird communities in managed wetlands of varying water depth. Water Birds, 23, 45–55.
Conway, D. (2000). The climate hydrology of the upper Blue Nile River.The Geographical Journal , 166(1), 49–62.
Delannoy, C. (2010). Important Bird Areas in the Caribbean: Key sites for conservation. Caribbean Journal of Science , 46(2-3):356(2010). https://doi.org.
Dejen, E. (2003). Ecology and potential for fishery of the small barbs (Cyprinidae teleostei) of Lake Tana, Ethiopia. PhD Thesis, Wegeningen Agericultural University, Wageningen, the Netherlands.
Ethiopian Wildlife and Natural History Society (EWNHS). (1996).Important bird areas of Ethiopia : A first inventory. Ethiopian wildlife and natural history society, Addis Ababa, pp 300.
Froneman, A., Mangnall, M.J., Little, R.M & Crowe, T.M. (2001). Water bird assemblages and associated habitat characteristics of farm ponds in the Western Cape, South Africa. Biodiversity and Conservation,10, 251–270.
Gaston, K.J., Blackburn, T.M., Greenwood, J.D., Greroryx, R.D., Rachel, M.Q & Lawton, J.H. (2000). Abundance-occupancy relationships.Journal of Applied Ecology, 37, 39-59.
Genet, Y. & Ejigu, D. (2017). Diversity, relative abundance, and habitat assemblage of avian species in different vegetation strata of Apini and Dikuma forest patches, Awi Admistrative Zone, Ethiopia.Ethiopian Journal of Science and Technology, 10 (1), 33-50.
Holm, T.E & Clausen, P. (2006). Effects of water level management on autumn staging water bird and macrophyte diversity in three Danish coastal lagoons. Biodiversity Conservation, 15, 4399-4423.
Hosteler, M. E & Martin, M. B. (2001). Florida monitoring program: Transect and point count method for surveying birds. University of Florida, pp 28.
Jeffery, C., Diane, M., Debinsi, O., Jakubausk, S & Kelly, K. (2004). Beyond species richness, community similarity as a measure of cross taxon congruence for coarse filter conservation. Conservation Biology, 18,167-173.
Esayas, K. (2011). Species composition, relative abundance, and distribution of avian fauna of Entoto Natural Park and escarpment, M.Sc. Thesis, Addis Ababa University, Ethiopia
Knight, R.L., Clarke, R. A & Bastian, R.K. (2001). Surface Flow (SF) treatment wetlands as habitat for wildlife and humans. Water Science Technology, 44, 27-37.
Lantz, S.M., Gawlik, D. E & Cook, M.I. (2011). The effects of water depth and emergent vegetation on foraging success and habitat selection of wading birds in the Everglades. Water Birds, 34, 439-447.
Lee, P & Rotenberry, J.T. (2005). Relationships between bird species and tree species assemblages in forested habitats of eastern North America. Journal of Biogeography, 32, 1139-1150.
Lepage, D. (2021). Avibase. Bird checklists of the world, Ethiopia. http://www.african bird club.org/countries/checklist.
Liordos, V. (2010). Foraging guilds of water birds wintering in a Mediterranean coastal wetland. Zoological Study, 49, 311-323.
Manhaes, M.A and Ribeiro, L.A. (2005). Spatial distribution and diversity of bird community in an urban area of southeast Brazil. Brazil. Archives Biological Technology, 48 , 285-294.
Marie, L., Paguntalan, J & Godfrey, J.P. (2008). Significant records of birds in forests on Cebu Island, Central Philippines. Fork tail,24, 48-56.
Marone, L. (1991). Habitat features affecting bird spatial distribution in the montane desert of Argentina. Australian Journal of Technology, 1,77–86.
Molla, M., Ejigu, D. & Yitayih, Y. (2021). Species composition, relative abundance, and habitat association of avifauna in Zegie Peninsula forest patches and associated wetlands, Bahir Dar, Ethiopia.International Journal of Zoology, 2021, 1-12. Article ID 9928284,