Diversity and Abundance of Avian Species of Owena Multipurpose Dam, Ondo State, Southwest, Nigeria

Birds have been considered as useful biological indicators because they are ecologically versatile and inhabit all kinds of habitats [1]. Wetlands are fringe habitats between terrestrial and aquatic ecosystems [2]. Many authors, notably Wilkinson, Berg, Beury, Ramsar believed that wetlands are highly important habitat for diverse fauna including mammals, birds, fishes, reptiles, amphibians, and aquatic invertebrates [2-4]. However, the importance of wetlands depend on many factors namely; wetland size, connectivity to surrounding areas, diversity of vegetation, water quality, food resources and topography [5]. According to James et al. the use of wetlands and their resources is widespread among many diverse bird taxa of the world. Birds use wetlands for breeding, nesting and teaching young, as a source of drinking water, for feeding, resting, shelter and for social interaction [6]. Wetlands provide food for birds in the form of plants, vertebrates, and invertebrates [4]. The aquatic avifauna is quite susceptible to the changes in wetlands. This helps us to know whether the area is ecologically healthy or getting polluted, as total absence of birds from an area may be considered as pollution indication or human disturbance such as excessive hunting or human pressure [7]. Submerged vegetation can attract a higher number of migratory birds in freshwater bodies [8]. According to the relation between wetlands and birds is shaped by many factors [9]. These include the availability, depth, and quality of water; the availability of food and shelter; and the presence or absence of predators. Birds have daily and seasonal dependencies on wetlands for food and other life-support systems. Niemi stated that avian adaptations to utilize wetlands and other aquatic systems are diverse and include anatomical, morphological, and behavioral changes [10]. James et al. stated that because numerous bird taxa depend on these critical habitats, wetlands are important components in the conservation and management of continental populations of ducks, shorebirds, and other wetland -dependent species [11].


Introduction
Birds have been considered as useful biological indicators because they are ecologically versatile and inhabit all kinds of habitats [1]. Wetlands are fringe habitats between terrestrial and aquatic ecosystems [2]. Many authors, notably Wilkinson, Berg, Beury, Ramsar believed that wetlands are highly important habitat for diverse fauna including mammals, birds, fishes, reptiles, amphibians, and aquatic invertebrates [2][3][4]. However, the importance of wetlands depend on many factors namely; wetland size, connectivity to surrounding areas, diversity of vegetation, water quality, food resources and topography [5]. According to James et al. the use of wetlands and their resources is widespread among many diverse bird taxa of the world. Birds use wetlands for breeding, nesting and teaching young, as a source of drinking water, for feeding, resting, shelter and for social interaction [6]. Wetlands provide food for birds in the form of plants, vertebrates, and invertebrates [4]. The aquatic avifauna is quite susceptible to the changes in wetlands. This helps us to know whether the area is ecologically healthy or getting polluted, as total absence of birds from an area may be considered as pollution indication or human disturbance such as excessive hunting or human pressure [7]. Submerged vegetation can attract a higher number of migratory birds in freshwater bodies [8]. According to the relation between wetlands and birds is shaped by many factors [9]. These include the availability, depth, and quality of water; the availability of food and shelter; and the presence or absence of predators. Birds have daily and seasonal dependencies on wetlands for food and other life-support systems. Niemi stated that avian adaptations to utilize wetlands and other aquatic systems are diverse and include anatomical, morphological, and behavioral changes [10]. James et al. stated that because numerous bird taxa depend on these critical habitats, wetlands are important components in the conservation and management of continental populations of ducks, shorebirds, and other wetland -dependent species [11].
In all the three types of wetlands (marine/coastal, inland or manmade), the most significant point of reference is water management. The water demand in Ondo State, Nigeria increased tremendously over the years rendering the facility to become grossly under-dimensioned for the intended towns and villages, a development that called for a much larger supply scheme. Consequently, the Ondo State Government in 1976, commissioned the design of the Owena River Dam with the objective of supplying raw water from the resulting reservoir for the existing water scheme, but taken over by the Federal Government of Nigeria (through Benin-Owena River Basin Development Authority) and converted it to a multipurpose use in line with the functions of the River Basin Development Authorities. The design was reviewed to include in addition to provision of potable water, usage for irrigation of 3000 hectares of farmland, fisheries, as well as generation of hydroelectric power. The dam, sited on the Owena River about 14 km upstream of the old Owena water scheme, was designed to create an impoundment of 36.25 million cm 3 gross capacity, covering an area of approximately 7.38 km 2 at the normal water level [12].
Construction of large dams have led to the extinction of many aquatic species, the disappearance of birds in floodplains, huge losses of forest, wetland and farmland, erosion of coastal deltas, and many other immitigable impacts. Consequently, habitat loss and alteration causes the degradation of breeding sites, water level stabilization, sedimentation, nutrient inputs, invasion of exotic plants and animals [13][14][15]. Therefore, species' responses to habitat loss are a central issue of contemporary conservation biology [16]. This study will make comprehensive baseline information of the birds in this area for the future as well as to create awareness for their conservation in the area.

Materials and Methods
The study area The dam is about 300 m long and 9 m in its deepest part. It covers an area of about 790 sqkm. The dam is supplied with water from the Owena River and it covers an appropriate surface area of 7.8 sq km. Currently, the water from the dam is to feed the 60,000 m 3 /day capacity water treatment plant built beside the dam. Fishing activities by registered local fishermen are also presently taking place within the dam lake [12]. The annual mean temperature is 27.3ºC, annual rainfall ranges from 1150 mm-2000 mm. Some common plant species in the area includes, nymphaea alba, eichhornia crassipes, ludwigia peploidies, panicum rapens, anacardium occidentale, ficus capensis, albizia zygia, polygonum lanigerium and also have different species of reptiles and amphibians.

Data collection
The line transect method as described by Bibby et al. was adopted for the survey. A total of five transects were placed at existing paths, tracts, and the river bank in the study area [17]. The length of each transect varied and ranged from 350 m-1000 m depending on the prevalent situation in the area. The transects were visited thrice. During each visit, transect were walked slowly and at every 50 m interval the observer stop for some minutes (10 minutes) to observe bird species. Readings were taken at intervals of each point with the help of Global Positioning System (GPS).
Surveys were carried out during early mornings (7.00-10.00 hr) and the evenings (16.00-18.30 hr.). The start time and end time for each transect was recorded. All birds observed or calls heard and recorded including those in flight were identified. A pair of binocular (Barska 8 × 32 with 8MP Digital camera) was used to aid in the identification of birds sighted while voice recorder (Sony digital voice recorder) was used to record bird calls and later played back to confirm through the call of birds downloaded. Birds recorded were categorized to species, family and order with the aid of field guide book on West African Birds by [18].  [19,20].

Calculations
Relative abundance (%) of bird species was calculated using the expression: Where n=Number of recorded bird species N=Total number of birds observed [21].
Diversity Index: Shannon-Weiner diversity index was calculated using PAST ((Paleontological statistics software package for education and data analysis) statistical software [v. 16]. The equation is given as:

Statistical Analysis
Data obtained were analyzed by both descriptive and inferential analysis. Diversity indices were determined using the PAST ((Paleontological statistics software package for education and data analysis) statistical software [v. 16] [11]. Significance in mean bird density in the two seasons was determined using T-test while One-Way ANOVA was used to test for significance in bird diversity indices in the four transects.

Results
A total of 35 bird species belonging to 20 families and 10 orders were identified and recorded in the study area. The common species in the study area includes Great egret (Ardea alba), Spur winged lapwing (Vanellus spinosus), Grey heron (Ardea cinerea), Great cormorant (Phalacrocorax carbo), Black Kite (Milvus migrans), Squacco heron (Ardeola ralloides), African jacana (Actophilornis africanus), Long Tailed Cormorant (Microcarbo africanus) and Cattle egret (Bubulcus ibis) as shown in Table 1. However according to IUCN 2015 status categorization all the bird species recorded were in the Least Concern (LC) category. The table also shows that bird species were categorized into seven feeding guilds; Insectivores, Frugivores, Omnivores, Nectariivores, Granivores, Piscivores and the Carnivores. The order Passeriformes had the highest number of families (9) and species (17). This was followed by Pelecaniformes and Charadriiformes with 2 families each, (4) and (2) species respectively. The Columbiformes, Coraciiformes, Suliformes, Accipitriformes, Cuculiformes, Galliformes and Anseriformes had one family each as shown in Table 2.
The hirundinidae family (Figure 2) had the highest number of species (6)  The total mean number of bird was 428 ± 5.75 individuals per observation (Table 3). However Fire finches (Lagonosticta sanguinodorsalis) had the highest mean number (156.4 per observation) and relative abundance of 36.54% (n=782). This was followed by village weaver (Ploceus cucullatus) with mean number of (136.6 per observation) and relative abundance of 31.92% (n=683). In contrast, grey heron (Ardae cinerea) and great cormorant (Phalacrocorax carbo) had the lowest mean number (0.2 per observation) and relative abundance of 0.05% each.
The result of the diversity index (Table 4)

Discussion
Wetlands are of great variety and birds' adaptation as well as usage of wetland environment varies greatly from species to species. Differences in resources availability between habitats such as breeding sites, roosting materials, cover, food and water restricts some species to certain type of habitat while allowing others to be widely distributed.
The study recorded 35 species of birds some of which are dependent on wetland such as jacana, herons, spur winged lapwing, egrets, white faced whistling duck, cormorants. Others such as weavers, finches, swallows, bee-eaters, whydahs, and mannikins are not wholly dependent on the dam. Though all the bird species recorded were under the Least Concern category of IUCN Red Data List, however, there is the need to ensure that the birds are conserved so that the local population will not decline. Bird species diversity index was low in the area but higher number of bird species and individuals were recorded in transect 1 and 5 which is located in open areas where structures such as buildings, electric poles and wires, and farmlands which have more grasses and shrub cover than in the other three transects (2, 3 and 4) along the banks of the dam. This agrees with the finding of Clergeant et al, Chale, Wash, Sandstorm et al [22][23][24]. that human disturbed areas provide heterogeneous habitats which attracts human tolerant bird species. Species that can co-exist with humans such as mannikins, swallows, pied crow, village weaver, common bulbul, finches etc. were recorded in the two transects.
Birds like white faced whistling duck were found on the vegetation on the water while spur winged lapwing were found at scattered shores. The grey heron recorded was found on a tree. The squacco heron were found during the survey majorly on the bare ground feeding along the mudflats on fishes and other vertebrates. However, African  jacanas' were found mostly around shallow area of the dam walking on floating vegetation to pick up insects and vertebrates from the floating vegetation. This can be attributed to the heterogeneity of the habitat which is in support of what Weins stated in his research that the species composition of a specific area is inter-linked to the available resources in the area which includes physical structures of the habitat, food availability and biotic factors [25].
The granivores, insectivores and canivores were more abundant than the nectarivores and frugivores. This is as a result of the disturbance/alteration to the ecosystem through the construction of the dam. This is in agreement with the findings of Odewumi et al. who reported that infrastructural development can lead to changes in bird species composition and abundance [19][20][21][22][23][24][25][26].
During the late dry season, the river level was extremely low and more birds were sighted especially black kite and white-faced whistling duck but in the rainy season, the water level was high and few birds were sighted. It was also observed that the population of black kite has reduced drastically as a result of their migration which may be due to them not having access to their prey. This may also be connected to reduced fishing activities in the rainy season in the area.    The finding of this study revealed that construction of dam in the study area has led to the presence of species associated with different habitat types and with different feeding habit. The vegetation along the banks of the dam provides food, nesting place and hide out for some bird species recorded in the area. It is therefore recommended that the management programme for the Owena dam should incorporate avian conservation in the area. Human activities that could be detrimental to the conservation of bird should be discouraged in the area. Regular monitoring of the sites should be carried out so as to control changes in the state of wetland ecosystem.