Most of the tropical rainforests are subject to both anthropogenic and natural disturbances. Forest elephants (Loxodonta cyclotis) cause forest clearings within the tropics. This study was conducted at mid-elevations (1100–1700 m a.s.l.) in Mount Cameroon National Park. We assessed the difference in the structure of bird communities in the forest and areas located nearby affected by elephant activities. We used the point-count method; 22 points were established within each habitat. The vegetation was visually estimated within a 50 m radius surrounding each counting point. In total, 1603 birds from 85 species were recorded. The vegetation cover from 3 to 5 m at points with elephant activity was significantly lower compared to points without elephant activity. Bird species richness was significantly higher around points in pasture compared to points in intact forest. Habitat type and the percentage of vegetation layer from 3 to 5 m significantly impacted the bird community structure. The points in the pasture were especially characterized by the increased abundance of some open habitat species (e.g., Chubb’s Cisticola chubbi). Few studies have documented the effects of elephant activity on other species, although the effects are widely stated as important drivers of habitat diversity in tropical forests. In conclusion, disturbance caused by elephants leads to increased bird community diversity due to the increased heterogeneity of the environment, which documents the high importance of elephants as ecosystem engineers.
While birds are known to show preferences for distinct vertical strata in forests, detailed studies on the vertical distribution of whole communities are still scarce. Furthermore, of those conducted, most have used ground‐based methods, including in both tropical and temperate forest. Here, we utilised ground‐to‐canopy mist nets to explore the vertical distribution of birds within lowland forest of Mount Cameroon National Park in both dry and wet seasons. In total, 908 birds from 83 species were caught. Species richness was highest in the understory and decreased towards the canopy as did bird abundance. We sampled more species during the dry season, with some species showing substantial seasonal changes in overall abundance. No seasonally driven stratal shifts in abundance were observed, while species richness increased in denser strata in the wet season. Although frugivoro‐insectivorous birds represented the most species‐rich foraging guild, their total abundance was unrelated to height above the ground, season and vegetation cover. This was also applied to gleaning insectivores, the second most species‐rich foraging guild. Omnivores, insectivoro‐nectarivores, sallying insectivores and frugivores typically showed a preference for higher vertical strata, while ground‐foraging insectivores preferred low forest strata with dense vegetation. Seasonal variation was most profound in frugivores and sallying insectivores.
The distribution of birds in the tropical mountains is important not only for testing fundamental scientific hypotheses, but also for bird conservation. In order to obtain knowledge on bird community structure within the tropical highland ecosystem, we used ground-to-canopy mist nets to assess bird species distribution along a vertical ground-to-canopy gradient for two elevational bands on Mount Cameroon. The study area included lowland forest (Drink Garri, 650 m a.s.l.) and montane forest (Mann’s Spring, 2200 m a.s.l.). We mist netted a total of 2658 individuals, including recaptures, belonging to 118 species from 50 genera. NLAG (net location above the ground), vegetation cover and locality significantly affected the bird communities. The composition of avian communities strongly differed between the two elevational bands. Species diversity considerably decreased with NLAG in both localities and increased with increased vegetation cover at the low elevation site. Species dietary guilds were significantly influenced by the seasonality, elevation, NLAG and vegetation cover. For most of the feeding guilds included in the study (frugivores, omnivores, insectivores, granivores and nectarivores), we found a negative correlation between the abundances and vegetation cover. Meanwhile, percentages of abundance of frugivores, nectarivores and omnivores showed a positive correlation with NLAG. We discuss the substantial changes in feeding guild structure along a vertical gradient and between two elevational bands. In conclusion, Mount Cameroon’s forest vegetation structure differs between two elevational bands and along vertical gradients from ground to canopy, considerably affecting the bird community structure.
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