A Preliminary Study on Land Use Effects on Birds Diversity in the Selected Agro-Ecosystems of Ekiti State, Nigeria

Introduction

The significance of land use type near wildlife habitats has been recognized globally as the major drive of biodiversity loss [1, 2, 3]. Roughly one- third of the global land area is devoted to cultivated land use system and as a consequence more area is expected to be converted to agricultural land use practices. Conservation in the tropics has its focus on pristine habitats such as rainforest [4], due to high level of biodiversity presence whereas human dominated landscape have been all but ignored in tropical ecological and conservation research as they support lower species diversity [5]. Over the last 30 years the natural habitats has been dwindling in area, which necessitates much of wildlife relocating and relies on land heavily used by humans and that the types and scale of land use types can have a marked influence on the wildlife populations’ structure [6, 7]. Consequent upon the spreading of agricultural landscapes decreasing at an alarming rate and pristine habitats shrinking, survival of many biodiversity invariably become the function of the types and patterns of land use which must be understood in order to incorporate these lands into conservation management plans. Land use can be a major source of feeding and breeding site for birds and a temporary or permanent habitat for some species [8]. Land use for agricultural purposes such as shade–grown cocoa was reported to harbour high biodiversity due to the presence of diverse high canopy forming species, complex forest structure, and absence of invasive exotic weeds [9].

Such land use type often provides suitable habitats for native fauna and were especially good for birds. In contrast, sun-grown monocultures plantation of Cocoa, coffee and oil palm were found to have adverse effects on biodiversity due to homogeneity and presence of invasive weed species [10]. Most deforestation has taken place in biodiversity rich tropical forests, these areas are expected to face even more pressures in the future, due to agricultural expansion. Conversion of natural habitats, especially intact old-growth forest to agricultural and pastoral lands is among the greatest threats to biodiversity in the recent times. Land use and its management have a major impact on natural resources including water, soil, nutrients, plants and animals and tend to vary from one country to another [11]. Land use could result into complete transformation, such as transforming a forest land to the settlement land or it could involve partial transformation through retaining the primary status of the land such as vegetation covers [12]. In most tropical forest areas, agricultural lands are predominant types of land use around native forest patches [13], but their influence alone on the persistence of fauna diversity in some tropical regions is poorly understood. Agricultural lands can be essential components in biodiversity conservation within tropical forest–agricultural landscapes if properly managed [14]. The isolation of protected areas as the sole means of protecting biodiversity is insufficient given the current trend in land use dynamics [9]. Many studies have demonstrated the potentials of diverse land uses in supporting biological diversity and stress their integration in conservation strategies [15]. Land uses when properly managed to an extent will not only support a large number of biodiversity but also serve as safe corridors that will permit dispersal of wildlife between patches [16]. Perfecto and Vandermeer [17] proposed that managed agricultural areas were equally important as the forest patches they surround. In their study, they found that species richness of ground-foraging ants in a well shaded organic Cocoa farm did not differ from that of a nearby Montane forest. Similarly, Harvey, et al. [18] confirmed the conservation value of agricultural lands, mainly areas that retained an abundant native tree cover. Such areas as suggested, often exhibited structural heterogeneity while providing habitat and resources for native fauna species [19]. It is known that tree and bird species are most sensitive to change and hence the most critical indicators of the biodiversity impact of land use conversion [20]. Ekiti state is among the areas that have severe land transformation due to various forms of human economic activities. These have resulted to intensive degradation that has transformed most of the natural environment, which in turn influence rate of biodiversity loss [21]. One of the pertinent challenges with which nature conservationist will be confronted within the nearest future will obviously be the discovering the relationship that exist between the changing environments and how land uses as the major driving force in the alteration of pristine ecosystems can be managed effectively to accommodate both human needs and biodiversity conservation. Hence there is a great need to establish the contribution of various forms of land uses on the sustainability of biodiversity.

Discussion

The species abundance in this study varies between the four land uses. The highest bird species abundance was recorded in the Gliricidia sepium plantation land use may be due to reasonable food resource availability in this land use type. The nature of arable farming activities existing within and around the Gliricidia sepium plantation may further influence and added to the diverse availability of food for different birds in the habitat. The study conducted by Soka, et al. [26] in Hombolo wetland shows that wetlands provide habitation and aided bird species abundance and richness because they serves as source of food to birds, supports the findings of this study. In regard to the structure of bird communities in the different land use types, birds’ diversity is higher in the land uses with high vegetation diversity as occurred in the natural forest. The natural forest examined in this study has mixture of vegetation features, tall large fruit bearing tree species with a wide canopy cover, trees with high diameter at breast height, dead wood stands and the greater diversity of birds in this land use type may be ascribed to these vegetation features and agedness of the habitat. The diverse vegetation flora and features play important roles in the provision of food to birds, support bird nesting, provide good cover for birds hiding place, make available variety of placements for nests, protection against predation and pleasant microclimate for bird species. Soka, et al. [26] asserted that the availability of diverse foods make birds of different feeding guild to dominate an area. Vegetation cover has been reported to have a strong influence on avifauna diversity [27]. The monoculture land use types including the gliricidia plantation present in the farming areas have reasonable bird diversity and richness but most bird species identified in the land uses were generalist with fewer forest dependent species. The overall result of this study shows consistency with the findings of Harvey and Villalobos [13] that agro-monoculture plantations harbor birds that are as abundant species rich and diverse as natural forest habitats. Fjeldsa [28] asserted that habitat disturbance creates increased habitat edge resulting in loss of specialist bird species and immigration of generalist species. The high levels of vegetation alteration as vividly observed in the mono agricultural plantation land uses may invariably be responsible for the heterogeneity in the avian order, families and species composition in the selected four land use types. Elmquist, et al. [29] asserted that nature fragmented system and habitat disturbances lead to loss of specialist species and encourage the generalist species. However, the structure of the monoculture land use types has been distinctly altered which led to the habitation of fewer forest dependent species, so bird diversity is more closely related to the structure and floristic characteristics of land use types. The land use specific relative abundance estimates vividly revealed that 17, 20, 12 and 32 bird species recorded in the Cashew, Cocoa, Gliricidia plantation and Natural forest respectively were in rare birds category and that higher percentages, 77%, 83% and 96% of birds recorded in Cashew, Cocoa and the Natural forest respectively, while extremely lower percentages fell into the uncommon and frequent relative abundance categories. The result of the relative abundance category of this study negates the findings of Cody [30] and Igl and Ballard [31] that reported that habitats dominated by woody vegetation or habitats that are structurally and floristically more diverse favours higher relative abundance categories, which was not the case in the present study because none of the bird species recorded were in common or abundance category even in the natural forest considered in this study. The foraging habits of the bird species identified in the selected land use types may explore the variation in flora composition and structural diversity of the land use types, which in accordance with the findings of Pearman [32] that variation in vegetation floristic and structure influences the distribution of bird foraging guilds. Eleven feeding guilds were identified in the study and insectivores were the most dominant group. The insectivorous feeding guild was mostly consisted of bird species from families Cuculidae and Bucerotidae such as Red chested cuckoo (13) and African pied hornbill (3) respectively. In the cashew and gliricidia plantation, the insectivore species were the most abundant species while insectivores’ species diversity was found to be highest in the natural forest land use type. This result outcome is fairly in agreement with the discovery of Blake and Loiselle [33] that insectivore’s species often rank higher in species richness and abundance in tropical forests while Rajaskekara and Verkatesha [34] reported the occurrence of higher numbers of insectivores in agroforests. The availability of a variety of food sources for both adults and young birds within and around the plantation land uses may be responsible for higher frequency of occurrence and abundance of insectivore’s species recoded in the study. On the other hand, the insectivores in the cocoa plantation recorded the same value which was obtainable in the other two plantations which is an indication that the frequency of spraying of the farm with insecticide has no pronounced effects on the activities of insects. The next predominant abundant trophic guild group in the land uses was carnivorous birds with African black kite (4), tawny eagle (4) and common kestrel (6) as the most prominent species which were mostly sighted in the cocoa plantation land use where abundance of food sources, such as frogs, snails, squirrels, rats and other small vertebrate species were readily present. Stafford, et al. [35] stated that the abundance of carnivorous bird species in rice fields may be due to the large quantity of food resources, such as polychaetes and mollusks in the rice plots during the migration season. The granivores feeding guild ranked next to carnivores and the granivorous species with higher frequency of occurrence were laughing dove (16), Red-eyed dove (14) and Black and white manikin (10). The nectarivore feeding guild were also more prominent in species richness and abundance in the gliricidia and cashew plantation than in the other land use types, this may be due to the presence of higher flowering intensity in the land use types, the most frequently observable nectarivore bird species were the sunbirds in the family Nectarinidae. Fleming [36] was of opinion that the structure and composition of avian communities changes in space and time with the availability of food resources and that variations are observed to be most visible among birds that feed on patchy and temporary food resources, like nectar and fruit. Cotton [37] found that the abundance and diversity of nectarivores are correlated with an increase in nectar availability. Fewer species of nectarivores inhabits agroecosystems negates the findings of the study. The frugivores were found only in the natural forest land use type and were completely absent in other land uses. The abundance of the available fruit resources may be one of the reasons for the high frugivore bird species richness and abundance in the natural forest. The abundance and richness of fruiting plants is crucial and relates positively with the diversity of frugivorous bird species and foraging behavior in certain habitat types [38]. Finally herbivores were the not abundant in the four land use types and were completely absent in the natural forest. The study provided findings on the effects of land uses on bird species diversity in Ekiti State and the results finding showed that the presence of diverse food sources is highly influential to the diversity and abundance of bird species in the study.

Conclusion

Birds are critically important in the ecosystem as they act as biological monitors, alerting people about what is happening in an environment. Therefore, it is necessary to have a data base for the land use effects on bird species diversity in Ekiti State. The result of this study revealed the variation in the diversity, abundance and distribution of birds in the study land uses and their most preferred land use type. The birds found were mostly insectivorous species and have the highest species composition and abundance in the natural forest and gliricidia plantation respectively. The relative abundance of birds encountered during the study fell mostly on rare category. The fact that more species of bird were not observed does not indicate that birds were totally absent in the study land use but it is an indication that the families of birds were also rare in the land use types and express the urgent need to map out effective strategy for the conservation of birds in the land use types of Ekiti State.