Preliminary Assessment of Avian Diversity of Ayede Wetland in Ekiti State, Nigeria

Introduction

The Nigerian Avifauna is rich and diverse as the environment itself. This is because Nigeria is such a large country, stretching from the beaches and Mangrove swamps of the Gulf of Guinea through the remnants of the rainforest to the Savannas and thorn scrub of the North, which provides habitat for a fascinating variety of birds. Birds are important component of many ecosystems, even though their biomass is usually less than that of mammals. Nigeria has some of the most beautiful and interesting birds in the world. Ogunyemi & Olujobi [1] reported that Nigeria possesses high diversity of birds in West African sub-region and that the various ecosystems provide niche for diverse species of birds. In Ekiti State, Nigeria, the vegetation and wetlands contain a diverse avifauna resource. Although formerly abundant, many species have become rare and may be threatened with extinction. In physical terms, the last two decades have witnessed an accelerated rate of habitat destruction. This results principally from a combination of population expansion and direct government action. Birds’ population and distribution especially in the wetlands have been affected by this unprecedented rate of habitat destruction. Clergeau, et al. [2] asserted that rapid increase in the alteration of natural habitats is the main threat to the forests and wetlands biodiversity. Many specialist species inhabiting an ecosystem are unable to adapt to disturbed environment [3]. The preparation of checklist of birds inhabiting an area is basic to the study of bird diversity [4, 5]. It is a well-known fact that the concentration of threatened bird species is greater in the tropics than in other continents of the world. Of the 1,029 threatened species, 884 occur in developing countries [6]. Thus the conservation of threatened bird species has to be properly addressed in the development nations of the world, if the threatened species are to continue their existence. The objective of the present study was to investigate the species composition, abundance and distribution of bird species inhabiting the Ayede wetland, Ekiti State, Nigeria in order to facilitate the development of comprehensive management plans for efficient and effective conservation of birds in the area.

Materials and Methods

The wetland of Ayede is the specific site where the present study was carried out. Ayede Ekiti lies within the tropics and geographically located between 7o 40’ N to 5o

15’ East of Greenwich meridian. The climate of the wetland area is tropical, with average temperature of 25°C all year round and high relative humidity. The annual rainfall varies from about 2500mm to 4000mm in the area. The pattern of rainfall distribution is unimodal with a long rainy season between April and October with a peak in August. The area is not protected and cultivation is carried out around the wetland. The wetland is typified by woodland vegetation and is characterized by remnants of forest, savanna tree and shrub species which co-exist side by side. The herb layer is dominated by grass and scattered trees. The trees are small with twisted boles. As a result of the arrival of savanna species, especially grassy materials which are highly inflammable in dry season, bush burning has become a major factor around the wetland. The most frequently occurring grass species in the wetland are Aristida kerstingii, Eleusine coracana, Eragrotis tenella, Sporobolus paniculatus. A preliminary survey was carried out in the month of January 2008. The physical features of the study area were assessed using ground survey. The geographical coordinates of the study site was taken. The study was conducted from January, 2008 to December 2009, which includes wet and dry seasons in the area.

Results and Discussion

Ayede wetland is situated in the Northern part of Ekiti State, Nigeria. It ranges from 597km (length) to 536km (width). It is typified by woodland vegetation and is characterized by remnants of forest, savanna tree and shrub species which exist side by side. The wetland is surrounded by agriculture fields, where different crops are grown throughout the year. The remnant of plant and cereal grains left in the area after harvesting attracts bird species to the wetland. The dam premises of the wetland support various species of fishes, amphibians and water insects which serves as food for wetland birds.

A total of 73 bird species belonging to 15 orders and 24 families have been recorded from the study wetland (Table 2). Details such as common and scientific names, status and abundance of the bird species observed in the wetland are presented in Table 1. Water birds constitute 20.55% of the total number of birds observed while 79.45% were terrestrial birds. The order Passeriformes constituted the predominant group, representing 23.3% of families (n=7) and 31.9% of species (n = 23) (Figure 1). The families with the largest number of species were Accipitridae (n=12). It represented 16.4% of the total number of bird species inhabiting the wetland of Ayede (Table 2). Out of the totality of 73 bird species observed in the wetland, 66 (90.4%) were resident and 7 (9.6%) were migrant species (Table 3). Three (3) of migratory species were observed during the wet season while the remaining four (4) migratory species were recorded at the peak of dry season of the study period. Four bird species such as Slender-Billed Weaver (Ploceus pelzelni) African Black kite (Milvus migrans), Shelley’s francolin (Francolins shelleyi) and Black-Headed Weaver (Ploceus cucullatus) ranked highest in number in the wetland, while Little Sparrow Hawk (Accipiter minullus), African Marsh Harrier (Circus ranivorus), Lizard Buzzard (Kaupifalco monogrammicus), Yellow Spotted Barbet (Buccanodon duchaillui) and Red Bishop (Euplectes orix) were rarely observed (Table 1). The birds observed were found to inhabit varying habitat types surrounding the wetland. A

total of 959 individual bird species were counted during the study period of the year 2009 in the wetland. The fairly large number of bird species recorded in Ayede wetland may be as a result of the vegetation heterogeneity which invariably bring about the variation in food, cover availability, and micro-climatic variations. This agrees with the conclusion of Afolayan and Ajayi (1980) and Crowel [10, 11] that variation in species composition, abundance and diversity of animals are strongly influenced by the availability of food, water and cover in the habitat. The element of habitat disturbance is not pronounced in Ayede wetland which might be one of factors responsible for high value of bird species diversity recorded in the wetland. Moenting [12] asserted that habitat disturbance creates increased habitat edge, resulting in loss of habitat specialist species from the habitat. Water birds being generally near the top of most wetland food chains have been reported by Jayson and Matthew [13] to be highly susceptible to habitat disturbances and are good biological indicators of general condition of aquatic habitats. Further analysis of the bird species abundance in the wetland indicated that of the bird species that inhabits the wetland, 6 were rare, 1 was common, 39 were uncommon, and 27 bird species were in frequent category (Table 3).

Ayede wetland accommodates more of Waders water birds than swimmers and divers. Tak [14] asserted that Waders water birds represent the greatest species diversity among the water birds. Wader bird species like Little Grebe (Podiceps ruficollis), Night Heron (Nycticorax nycticorax) and Little Bittern (Ixobrychus minutus), that belong to the family Ardeidae were observed regularly wading through the water surface of the wetland.

The wetland dependent bird species such as white faced Tree Duck (Dendrocygna viduata), African fish Eagle (Haliaetus vocifer) Long-crested Eagle (Lophaetus occipitalis) and king fishers were observed throughout study period around Ayede wetland.

The tree species of Lophira alata, Combretum molle, Cola acuminate, Garcini afzelli Phizophora racemosa, Baphia nitida, Parkia biglobosa, Albizia zygia and Spondias mombin present in the wetland environment provide cover to terrestrial residential birds inhabiting the wetland environment.

R = Resident, I = R = Resident, I = Immigrant, RA = Rare, C = Common, UC = Uncommon, f = frequent Table 1: Wetland Birds Recorded Around Ayede Wetland.

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