Bird Survey of the Abobo-Etetak Hill (Yaounde, Cameroon) and a Glance on the Avifaunistic Diversity of this Hill (Abobo-Etetak)

RESEARCH ARTICLE Bird Survey of the Abobo-Etetak Hill (Yaounde, Cameroon) and a Glance on the Avifaunistic Diversity of this Hill (Abobo-Etetak) Billy Nguembock, Mahamat Sali, Kemtchouan William, Azang Esther Diane Olivia, Guehoada Yollande, Factheu Clinton and Nkingop Djopmou Philippe Herve Laboratoire de Zoologie, Département de Biologie et Physiologie Animales, Université de Yaoundé I, BP 812 Yaoundé, Cameroun Département de Sciences Biologiques, Université de Montréal, C.P. 6128, succursale du Centre-ville, Montréal, QC, H3C 3J7, Canada


INTRODUCTION
More generally until now, avifaunistic studies performed in the Yaounde city did not particularly investigate the avifaunistic diversity of the sites in which birds have been caught and yet, there is a correlation between the food areas and the presence or absence of birds [13]. Thus, expressed through a diversity index, a quantitative measure could reflect for instance how many different taxa (families, genera, species, etc.) are in a dataset, and simultaneously takes into account how evenly the basic entities (individuals) are distributed among those taxa [14,15].
In this study, which was realized in the Abobo-Etetak hill during eight months, we mainly followed two aims: firstly, we thoroughly investigated the avifauna of this hill from base to tip and secondly, we tried to understand the distribution of this avifauna in their life environment.

Investigation of the Abobo-Etetak Avifauna
In order to investigate the avifauna, we used an appropriate method: the mist-netting method. According to this method, an inconspicuous mesh net is erected vertically on poles and deployed in areas of high activity to intercept birds as they go about their normal daily routines (Fig. 1).
We used dark-coloured nylon nets and smaller mesh for smaller species. Our mist nets were fixed with the mounting poles which were chosen carefully and the choice of an appropriate mist-netting site was important for the capture success (Fig. 1). To ensure the capture success, we mainly identified their preferred flight paths, feeding areas, roosting and shaded sites and that along the hill from the base to tip.
We began our capture very early in the morning (5: 00 AM) and we finished very late in the evening (sometimes 6: 30 PM). We used the same eight mist nets in our different field study and we did nine field studies during eight months.

Method for the Calculation of the Relative Abundance of the Abobo-Etetak Avifauna
In order to calculate the relative Abundance, we considered to use the Statistical Analysis System [16]. Otherwise, we used a software program Excel to obtain our histograms and curves [17].

Method for the Calculation of the Occurrence of the Abobo-Etetak Avifauna
In order to calculate the occurrence, we used the same software, the Statistical Analysis System [16]. The obtained results are frequencies as well as graphics.

Shannon Index (H')
The Shannon's diversity index represents the measure of the sum of degree of the uncertainty when it suggests predicting to which species would belong to an individual taken by chance in a collection of S species and N individuals. H' = 0 if the community has only one species; H' takes the maximal value log 2 S only when all species are represented by the same number of individuals. This index is determined by the relationship: Where pi = proportion of the individuals of the species "i"; S = total number of species of environment. The Shannon index (H') increases when the number of the species of the community grows and, theoretically, it can reach elevated values. The value of H' varies from 1 to log 2 S. In our study, the Shannon index was calculated with the Software PAST [18].

Simpson Index (λ)
The Simpson index represents the proportion of abundance of the species "i" [18]. This index measures the degree of concentration when individuals are classified into types. It is determined by the relationship: Where ni = number of individuals of the species "i"; n = total number of the individuals of the sample.
Nevertheless, the most popular of such indexes have been the inverse Simpson index (1/λ) and the Gini-Simpson index (1 -λ) and both have also been called the Simpson index in the ecological literature. In our study, the Simpson index was calculated with the Software PAST [18].

Equitability Index
The Equitability index measures the distribution of the individuals within species independently to the specific richness. Its value varies from 0 (supremacy of one species) to 1 (equal distribution of the individuals in species).
Thus, the Equitability index of Pielou (J') is determinated by the formula: H' max = log 2 S (S = the total number of the species).
In our study, the Equitability index was calculated with the Software PAST [18].
All these indexes have been obtained with a confidence threshold of 95%.

Familial Abundance of the Abobo-Etetak Avifauna
We caught 311 individuals belonging to 21 birds' families ( Table 1). The most representative family is the Ploceidae family with 119 of the 311 individuals (38.26%) with the Pycnonotidae family being second most abundant (14.79%; Table 4 and Fig. (2)). We found that 84.55% of the captures were from Passerine families and 15.45% from Non-Passerine families ( Table 1). The Ploceidae family was represented by four genera and eight species whereas the Pycnonotidae family was represented in the Abobo-Etetak avifauna by four genera and six species.

Diversity Index
The Shannon index was 2.24 at the familial level, 3.11 at the generic level and 3.34 at the specific level ( Table 5).
The Simpson index values were of 0.81 at the familial level, of 0.93 at the generic level and of 0.95 at the specific level ( Table 5). As for the Shannon index, the general tendency is the same as the Simpson index with the obtained values which are also high ( Table 5).
The equitability index values were 0.73 at the familial level, 0.85 at the generic level and 0.85 at the specific level ( Table 5). As for the two first indexes, the obtained values also appear far from 0 ( Table 5).

Avifauna of the Abobo-Etetak Hill
The survey accomplished on the Abobo-Etetak hill permits to highlight that Passerines birds were the most representative birds in this area with regard to Non-Passerines birds. Our study moves toward several surveys performed in Cameroon [1,6,7].
Thus, this study permits to highlight new families in the relic Centre Region of Cameroon and particularly in the Abobo-Etetak hill. Comparatively to previous records, we newly recorded species representatives of the non-passerines families (Lybiidae) as well as the passerines families (Motacillidae, Nectariniidae, Hirundinidae, Nicatoridae, Ploceidae and Monarchidae) in this area ( Table 1). Within the Abobo-Etetak avifauna, the most representative family is the Ploceidae family ( Table 1 and Fig. 2). The Ploceidae family commonly called 'weavers' gets this name because of their meticulously woven nests; these small passerine birds are gregarious, breed colonially and occur in several habitats (woodland, forests, forest edge, lowland forests, wet habitats, gardens, open or semi-open habitats, human habitation, grassland, etc.) [19,20]. Contrary to several other passerine families, their closest relatives still remain unknown and a future study in keeping with their phylogeny is long-awaited.
We found two new genera until now not encountered in this relic Centre Region, Cinnyris (the Nectariniidae family) and Terpsiphone (the Monarchidae family) ( Table 2). Except for these genera, most genera we found have been already recorded in this Region [1,6,7]. Among the genera met in this relic area, the genera Ploceus and Cyanomitra have obtained an occurrence frequency of 100% ( Table 2). The genus Ploceus is a representative of the Ploceidae family (see above) and the genus Cyanomitra is a member of the Nectariniidae family; African sunbirds are very small passerine birds which feed on nectar but in their youth feed on insects [19,21,22].
Among species collected in this area, we noted a lot of sedentary birds which are rarely dispersed more than a few kilometres from their natal sites (Eurillas latirostris, Camaroptera brachyura, Turdus pelios, etc.), seasonal birds which appear only seasonally in another part (Anthus brachyurus and Chrysococcyx caprius), intra-African migrant birds which breed in one part of Africa and spend the post-breeding season in a different area (Ceyx pictus) and vagrant birds which are outside their normal range (Hirundo fuligula) ( Table 4). Among the captured species, we highlighted two species of the Monarchidae family, the genus Terpsiphone, which are not found in the Guide [21] and they are probably new species; for this, we will do a molecular study in the future to clarify their situation.

Distribution and Diversity of the Avifauna in the Abobo-Etetak Hill Area
The Abobo-Etetak hill shows high avifaunistic diversity (see Table 5), with an absence of the supremacy of one species (H' = 3.34; Table 5). According to some authors [2,23], the montane vegetation grows on hills near Yaounde (at elevations of only 800-900 metres) and these semi-montane biomes offer the same feeding favourable conditions for all birds visiting or living in this relic area. Otherwise, it is documented that the distribution of many tropical bird species is closely related to a particular vegetation type [1] and more generally a correlation between food areas and birds is well established [13]. The Abobo-Etetak hill appears with the same vegetation from base to tip (secondary forest with in some places farmland). The distribution of the Abobo-Etetak avifauna corroborates practically this principle with the obtained value of the Equitability index (J'= 0.85; Table 5) which establishes the equal distribution of the individuals inside species.
The Simpson diversity index of 0.95 (1 -D = 0.95; Table 5) shows that the diversity within the Abobo-Etetak avifauna is established and this result goes in the same direction that the absence of the supremacy of one species as well as the equal distribution of the individuals of the species. Thus, all obtained values show that the Abobo-Etetak avifauna appears diversified; the diversity of this avifauna could be explained by luxuriant vegetation in this relic area all year round and this would have been favoured by a lesser competition between the individuals living in this hill. Otherwise the transformation of this area by human activities (particularly farmland) would have had an impact on the diversity of this avifauna with some genera captured in this hill (Ploceus, Passer, Estrilda, Pycnonotus and Spermophaga).

Scientific Interest of the Abobo-Etetak Hill Area
Contrary to several African regions, this relic Centre Region shows the Montane district at very low altitude (an altitude of less of 800 to 900 metres) whereas generally it begins in other African regions at an altitude of 1600 to 1800 metres [1, 2, 24 -26]. Thus, several new and endemic species have been described [3 -5] in this relic Region and certainly the two new taxa not found in the Guide [21] could be new species. Otherwise in spite of the urbanization as well as climatic changes, this Region preserves its originality in keeping with the fresh climate in an Equatorial area thus offering favourable conditions to birds all year around and receiving many European migrants' birds during the winter.