ABSTRACT
Ecological investigation of species diversity and relative abundance of birds was conducted from January to September 2017 at the shoreline of Lake Hawassa, SNNPR, Ethiopia. Three habitats namely-Tikurwuha wetland, Human settlement and Farmland were identified for the study. A total of 60 bird species under 14 orders and 37 families were identified. In general, 2720 individuals of 81 species of birds were recorded during the wet season and 1557 individuals of 49 species during the dry season. During wet season, Tikurwuha wetland habitat had the highest diversity (H’=3.469) whereas the lowest diversity was recorded in farmland (H’=2.864). Analogously, during dry season the highest and the lowest diversity were recorded in Tikurwuha wetland habitat (H’=2.845) and farmland habitat (H’=2.584), respectively. The overall seasonal species’ composition and relative abundance between dry and wet seasons were statistically significant (P < 0.05). In spite of the fact that the lake supports good number of birds’ populations, anthropogenic activities going on near the lakeshore such as farm land and human settlement expansions are shrinking available habitats to birds through altering the vegetation composition and structure that ultimately affects birds’ abundance and survival. Accordingly, since the existence of lakeshore bird species is based on the lake ecosystem, anthropogenic pressure such as farming activities and human settlement very close to the lake should be banned.
Key words: Birds, relative abundance, species composition, species diversity.
Ethiopia is a country endowed with great natural and cultural diversity. It covers an extraordinary number of the world's broad ecological zones with a high plateau and a central mountain range divided by Great Rift Valley. The country contains remarkable altitudinal range from the Danakil depressions in the Afar 100 masl (meter above sea level) to the mountain top of Ras Dashen in the north 4,620 masl. The diverse ecosystems endowed Ethiopia with a diverse biological wealth of flora, fauna, and microbes. Protected areas in the country comprise 21 National Parks, two Wildlife Sanctuaries, three Wildlife Reserves, 20 Controlled Hunting Areas, six Community Conservation Areas, two Wildlife Rescue Centers, two Community Managed Ecotourism and Hunting Areas, six Open Hunting Areas, three Commercial Ranches, two Botanical Gardens and Herbariums, four Biosphere
Reserves, 80 National Forest Priority Areas and three Municipal Parks (Weldemariam, 2016).
The country harbors 926 species of birds of which 639 are residents and 224 are regular seasonal migrants, including 176 from the Palearctic and 48 inter-African (Lepage, 2016). It is also indicated that 24 species are endemic to Ethiopia whereas additional 13 are shared only with Eritrea. So far in the country, 73 hotspots have been identified as Important Bird Areas (IBAs). Of these, 30 sites (41%) comprise wetlands, while the rest are representatives of other types of ecosystems. Nationally, Ethiopian IBA sites have been grouped into three conservation categories based on distribution and abundance as Critical (19), Urgent (23) and High (31) (Mengistu, 2003).Despite the rich bird assemblages in Ethiopia, due to enormous habitat degradation, fragmentation and loss, survival of many bird species including the endemic and globally threatened ones are endangered (Lepage, 2016). Particularly, expansion of agriculture, livestock encroachment and deforestation by the ever increasing human population has been often mentioned as the major causes of birds’ habitat degradation, fragmentation and loss in the country ultimately affecting their survival (Girma et al., 2011).
The lakeshore birds are among the most popular and interesting of birds. They are small to medium size characterized by slender, probing bills and longish legs (Laurent et al., 2012). Shorebirds come in many shapes and sizes, but all of them share certain characteristics, both physically and behaviorally. Nearly all shorebirds have a distinct preference for wet habitats and shorelines, both on coasts as well as along inland waterways, marshes or general riparian habitats most shorebirds are carnivorous and eat a range of insects, mollusks, crustaceans and worms. Physically, these birds have round heads; longer legs and very useful bills (Melissa, 2017).
Lake Hawassa is one of the most productive and aesthetically attractive rift valley lakes in Ethiopia with many ecosystem services. It is one of the eight rift valley lakes in the country and is among the first row of the places where people choose to have an outdoor recreation. The lake hosts diverse wildlife particularly avian fauna. However, although many former studies on the hydrology, water chemistry, fish diversity and other related researches on the lake have been carried out, ecological studies on lakeshore birds are not yet researched. Therefore, the study aimed at gathering primary information on the species composition and relative abundance of lakeshore birds around Lake Hawassa.
Description of the study area
Lake Hawassa is located in the Southern Nations Nationalities and Peoples Regional State (SNNPR) about 275km south of Addis Ababa with the geographical coordinates of 7°3’N latitude and 38°28’E longitude (Figure 1). It is the smallest of all the Ethiopian rift valley lakes having a total surface area of 95 km2 and a total drainage area of 1, 371.6 km2. Its mean depth is 11 m with maximum depth of 22 m. The lake is found at 1,686 masl which is about 16 km long and 8 km wide with an estimated water volume of 1.3 billion m3 (Zinabu, 2010). The average monthly maximum and minimum temperature of the study area is recorded in March (30.3°C) and December (10.0°C), respectively. Furthermore, the highest and lowest average rainfall records occur in September (233.8 mm) and December (0.2 mm), respectively (NMSA, 2016).
Lake Hawassa contains four main watersheds namely; the Ungauged sub catchment around the lake draining onto the surface of the lake, the Tikurwuha sub watershed draining through the Tikurwuha river, the Wondokosha and the Muleti closed sub watersheds (Yemane, 2004). The Lake is one of the freshwater shallow lakes found in the central Ethiopian Rift Valley. The sum totalities of aquatic and terrestrial habitats adjoining the lake facilitate the rich diversity of flora and fauna compared to other Ethiopian Rift valley lakes. Scores of species with sundry forms of flora, fauna and micro-organisms make the lake extremely rich in biodiversity (Sairam, 2014). The lake is among one of the biggest bird sanctuaries in the rift valley and homeland for several hundred species of water birds, including local and palaearctic migrants with large population of Marabou storks. Further, the lake is a major source of income through eco-tourism while the inhabitants depend on the lake for fishing and recreation (Sairam, 2014).
Preliminary survey
A reconnaissance survey was carried out for a week to be well acquainted with the study area. The area was divided into sampling strata and units that cover the whole area based on habitat type following Buckland et al. (2001). Three different habitat types found near the lakeshore were selected namely; tikurwuha wetland, human settlement and farmland.
Sampling design
Point count method (Manley et al., 2006; Lambert et al., 2009) was used to study abundance and composition of birds in the study area. Data were recorded by distributing points in the given habitat and selecting points from the distributed points on a random basis. (Geographical positioning System (GPS) was used to locate the geographical points for the bird counting stations. Accordingly, 10, 12 and 8 counting stations were used for tikurwuha wetland, human settlement and farmland, respectively. One counting station on each habitat was laid for 300 m length with a fixed width of 100 m (50 m on either side) and two times a month bird survey was made for each habitat. Numbers, types and locations of birds were recorded during a fixed amount of time at each point. Counting stations were marked using a conspicuous colored polyteen sheet at each station. The radius of point counting stations was set at bands based on the birds’ delectability test during reconnaissance survey (Norvell et al., 2003; Rosenstock et al., 2002).
Data collection and analysis
Data collection methods
Data collection was carried out from January 2017 to September, 2017. Hence both dry (January to May) and wet (June to September) seasons were considered (Amare, 2005). Bird identifications and counting of individuals were conducted by direct observation aided with binoculars. Observations were made by standing in the middle of the point transect and observing 360° round quietly and gently up to a distance of 50 m radius. Each point transect was 100 m far away from road side to avoid edge effect and 300 m far away from each other to avoid double counting of the same individual of a species following (Shimeles and Afework, 2008). Observation time of 5 to 15 min was used for the count depending upon how conspicuous the birds were. To minimize disturbance during the count, a waiting period of 3 to 5 min prior to counting was applied (Sutherland and Green, 2000). In each observation, bird species were identified and numbers of individual observed within the 50 m radius were recorded on data sheet prepared for this purpose. Data collection was carried out early in the morning from 06:00 to 10:00am and in the late afternoon from 04:00 to 06-30 pm when the activity of birds becomes prominent (Tsigereda, 2011). Identification and categorization of birds to their respective taxonomic groups’ done following field guide books (Sinclair and Ryan, 2003; Redman et al., 2009).
Hence, the abundance categories: < 0.1, 0.1-2.0, 2.1-10.0, 10.1-40.0 and > 40 were used. For each category, the following abundance score was given: 1(rare), 2 (uncommon), 3 (frequent), 4 (common), and 5 (abundant), respectively. Therefore, the relative abundance of each bird species was determined on the ordinary scale of rare, uncommon, frequent, common and abundant. Furthermore, by using SPSS (Version.22) software, Chi- square test was employed to determine the effects of season and habitat types on bird’s relative abundance and distribution.
Species composition
In the present study a total of 60 bird species belonging to 14 orders and 37 families were identified. Order Passeriformes was represented by the highest number of species (35%). Such higher representation of passerines or perching birds is common as Order Passeriformes is the largest and most diverse order of birds, comprising over half of the world's known bird species (Sibley and Monroe, 1990). On the other hand, the lowest number of species was recorded under Coliformes, Columbiforms, Cuculiform, Acciptriforms and Gruiform orders with one species each. Most of the birds in the study area were observed throughout the study period. Out of the total species recorded in the study area, two species (3.3%) were endemic to Ethiopia, three(5%) species were endemic to Ethiopia and Eritrea, 18 (30%) palertic migrant and 26 (43.3%) resident and the rest species were partially migrant (Table 1).
The present study revealed that lake Hawassa provides important habitat that supports large number of bird species including the two endemic species- Banded Barbet (Lybius undatus) and Thick billed raven (Corvus crassirostris) as well as other three species-Black winged love bird ((Agapornis taranta), Ethiopian Oriole (Oriolus monacha) and Wattled Ibis (Bostrychia carunculata) which are both endemic to Ethiopia and Eritrea. In addition, the occurrence of winter birds in a significant number (n=18) is an indication that the area is important site for migratory birds too. In a similar study that has been carried out at the southern tip of Lake Tana, 21 species of migratory birds were recorded (Shimeles and Afework, 2008).
Species composition of birds in different seasons was also computed for study sites. In general, during wet season the diversity of bird species in all habitat types was high. During this season, Tikurwuha wetland habitat had the highest diversity (H’=3.469) whereas the lowest diversity was recorded in farmland (H’=2.864). Moreover, the highest evenness record (H’/Hmax=0.9493) was from human settlement habitat whereas the lowest was in Tikurwuha wetland habitat (H’/Hmax=0.9176). On the other hand, during dry season the highest and the lowest diversity were recorded in Tikurwuha wetland habitat (H’=2.845) and farmland habitat (H’=2.584), respectively. The species evenness during this season H’/Hmax was 0.9529, 0.9054 and 0.9463 for human settlement, tikurwuha wetland and farmland habitats, respectively (Table 2). The overall seasonal species composition between dry and wet seasons was statistically significant (P<0.05).
Species diversity is the species richness in an area with consideration for species abundance. Richness is an indicator of the relative wealth of species. A combined measure of abundance and richness is however a crucial source of information in determining conservation priorities (Geofrey et al., 2013). The measure of species diversity in the area can be affected by several factors. The sampling method used (Pomeroy, 1992), the size of the study area (Bibby et al., 1998) and habitat heterogeneity (Pomeroy, 1992). Detection probability should also be taken into account because each species in a given habitat has its own probability of being detected, which is usually less than 100% (Shiferaw, 2008). In general, in all habitat types of the present study, bird species diversity during wet season was high due to high species richness and/or evenness.
A total of 60 species of birds belonging to 37 families have been recorded during the present study. Such record of the bird species showed that diversity is very high in the study area. Presumably, this is due to the availability of multiple and variety of alternative food resource and favorable climatic condition for nesting and breeding. According to Borgesio (2004) lakeshore habitats provide ample food resources such as fish, frogs, worms and insects to many bird species. Furthermore, De Filippo (2003) concurs with this idea by pointing out that birds require water as essential component of nutrition and medium for other activities. Among the three habitat types in the present study, relatively the highest species diversity was recorded in Tikurwuha wetland habitat. This is due to the fact that as compared to other habitats, anthropogenic activity in this habitat is very limited which in turn provides good food availability. Smith (1992) described that food resources are one of the key factors to determine species diversity in the particular area. Similar observation has been reported from a study conducted in LakeTana, Yiganda wetland (Shimeles and Afework, 2008). Moreover, high diversity generally indicates more complex and healthier communities since a greater variety of species are allowed for more species interactions hence, greater system stability. On the other hand, in the farmland habitat relatively less bird diversity was observed. This is due `to the fact that the area is covered with vegetables such as onion, cabbages, spinach and carrot and also maize is cultivated. These cash crops are cultivated twice a year in the study area by irrigation of water from the lake. Therefore, birds do not get adequate place for nesting and breeding. According to Meyer and Turner (1992), the conversion of wetlands for agriculture and urban industrial ports affect the nesting and breeding sites of many bird species. The use of irrigation from the lake is steadily increasing not only along the shore line of the lake but also in many of the natural drainage basins that used to recharge the wetland and eventually end up in the lake. In Ethiopia it has been revealed that expansion of agriculture altered the habitats of birds negatively impacting their abundance and distribution (Girma et al., 2011; Pennington and Blair, 2011).
Relative abundance
The relative abundance during the dry season was uncommon (6.6%), frequent (31.6%), common (41.6%) and abundant (20%). On the other hand, during wet season the abundance score was uncommon (8.3%), frequent (30%), common (43.3%) and abundant (18.3%). Rare species were not registered at both seasons (Figure 2). The occurrence of birds at different abundance score was also recorded in all study habitats during both dry and wet seasons. In general, the ‘common’ abundance category was predominant as compared to other categories irrespective of habitat types and season (Table 3).
Common bird species were very abundant in the study area due to the favorability of the area to satisfy their nutritional requirements during both seasons. These birds were observed foraging on food and water resources available around the lake. For instance, marabou stroke, Sacred Ibis, African Jacana and Hammer Kop were recorded in large number around fish market areas along the lakeshore of the study area. In human settlement areas where there are cafeterias, hotels and boating service delivery sites, White pelicans, Marabou stroke, Baglafecht weaver, Sacred Ibis, Royal spoon and Egyptian Goose were frequently observed foraging on leftover foods. The surrounding area of the lake is covered with dense strands of emergent, submerged and floating aquatic vegetation. Its surface and bottom provide lush habitats for a diverse variety of animal life and extends into swamps, creating an even greater diversity of inter-connected aquatic niches. This habitat diversity supported the floral and faunal richness of the ecosystem and rendered it a key feeding station for migratory birds.
The fishing activity in the lake affects many shore living birds; on the other hand around fish markets the head and internal parts of fish that are discarded during fish harvesting provide food for many bird species. In the present study, Marabou Stork, Great White Pelican, African Sacred Ibis, Little Egret, and Thick billed Raven species were frequently observed feeding on scraps of fish dumped by fishermen. Presumably, these birds forgo their natural pattern of foraging. Marabou storks and pelicans, in particular, were seen flying and crowed among AmoraGedel and Tikurwuhalake shore areas during the periods when fish scraps are dumped.
In the present study, relative abundance of bird species between seasons was significantly varied (P < 0.05). A total of 2720 individuals of 81 species of birds were observed during the wet season and 1557 individuals of 49 species during the dry season in the three types of habitats (Table 2). This could be due to the availability of food resources, habitat condition, breeding season and as well as the migratory behavior of the species. In a similar fashion Gaston and Blackburn (2000) explained that distinct seasonality of rainfall and seasonal variation in the abundance of food resource resulted in seasonal changes in the abundance of birds. Moreover, the temporal decoupling between food resource and bird number, variable climate harshness in different regions or the inability of individuals to reach isolated areas affect migratory bird population(Telleria et al., 2009).
In general, the lake shores are important feeding, and breeding sites for birds. Farmers along the shore of the lake cultivate the area when the water level recedes. Fruit trees such as mango and papaya and vegetables are becoming dominant in the study area. At present, the unusually high level of reduction in the size of the lake led many areas under permanent cultivation. Obviously, this could diminish bird’s habitat unless appropriate community based conservation measures are taken.
The study area is home for varieties of lakeshore bird species. Among these some are globally threatened species as well as endemic birds of Ethiopia. A total of 60 bird species were recorded in three different habitats. High diversity of bird species was recorded in Tikurwuha wetland area whereas low diversity in farmland area. Both species composition and relative abundance of birds varied between seasons. The availability of food resources, habitat condition, breeding season, migratory behavior and the like might contribute to such variation. Most of the birds in the study area are common in the three habitats. In general, the ‘common’ abundance category was predominant as compared to other categories irrespective of habitat types and season.
Presently, although the lake supports good number of birds populations, anthropogenic activities going on near the lakeshore such as farm land and human settlement expansions are shrinking available habitats to birds through altering the vegetation composition and structure that ultimately affects birds’ abundance and survival. Moreover, the leftover foods dumped from hotels, resorts and cafeterias surrounding the lakeshore affect the natural feeding habit and /or foraging behavior of birds as observed in Marabou Stork, Great White Pelican, African Sacred Ibis, Little Egret, and Thick billed Raven, in the present study.
Based on the result of the study the following recommendations are forwarded:
(i) As the existence of lakeshore bird species is based on the lake ecosystem, anthropogenic pressure such as farming activities and human settlement very near the lake should be banned.
(ii) Concerned authorities should give due concern to lakeshore bird species since these birds can be good sources for ecotourism.
(iii) To have complete ecological information about lakeshore bird species in the study area, additional ecological studies viz. feeding behavior, activity pattern, and reproductive behavior and so on should be studied in the future.
The authors have not declared any conflict of interests.
The authors are grateful to regional office of culture and tourism for providing us valuable information about the study area. Furthermore, we are very thankful to Arba Minch University for covering all financial expenses during the study.
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