Vertical stratification and seasonal changes of the avian community in Mount Cameroon lowland rainforest

Abstract

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.

Changes in Bird Community Structure on Mount Cameroon Driven by Elevational and Vertical Gradients

“…For detailed distribution of mist-netting sites within each elevation belt, see Supplementary material, Figure S1. Ground-to-canopy mist nets were used to study the vertical stratification and the distribution of forest bird species along a vertical vegetation gradient on Mount Cameroon (for a description, see [24]).…”

“…We sampled birds at two elevations (Figure 1 . Ground-to-canopy mist nets were used to study the vertical stratification and the distribution of forest bird species along a vertical vegetation gradient on Mount Cameroon (for a description, see [24]). At each locality, we established 17 mist-netting sites with known GPS coordinates where five to seven nets of 3 m height each were superimposed on each other, resulting in a continuous panel assembly of mist nets reaching a height of 15 or 21 m above ground.…”

“…The structure of vegetation cover within forests represents an essential component determining bird community structure [14], especially due to the distribution of food resources [15]. The vertical stratification of bird communities has already been studied in both temperate and tropical forests [16][17][18][19][20][21][22][23][24]. Meanwhile, the structure of the vegetation changes considerably with elevation [25,26], due to changes in abiotic (temperature, wind; [27]) and biotic conditions (predator, foliage density, food resources, high parasitism rate; [28]).…”

Long‐term capture data uncover shifts in the daily activity patterns of Amazonian birds

“…Compared to their temperate counterparts, tropical forest birds are more highly specialized, selecting more restricted microhabitats and foraging heights – together, this horizontal and vertical specialization results in reduced niche breadth (Marra and Remsen 1997). Although vertical stratification has been described for forest birds around the world (Orians 1969, Pearson 1971, Cody 1974, Pearson 1977, Terborgh 1980, Bell 1982, Fitzgerald et al 1989, Walther 2002, Chmel et al 2016, 2021), the tall rainforests of the tropics are widely believed to have the greatest vertical stratification (Allee et al 1949, MacArthur et al 1966, Smith 1973). Within these finely subdivided forests, birds that forage on or near the ground have the narrowest bands of vertical activity (Orians 1969, Cody 1974, Terborgh 1980).…”

An environmental habitat gradient and within-habitat segregation enable co-existence of ecologically similar bird species

“…Alternatively, Eltonian variables are affected by the presence of the species, operate at fine scales, and are density dependent. Ecologically similar bird species could partition their niches through attributes that characterize the Eltonian niche such as vertical stratification of feeding zones [ 21 ], variation in activity pattern [ 22 ], differences in diet and foraging behaviour [ 23 ], interspecific territoriality [ 19 , 24 ], body size variation [ 25 ] and within-habitat segregation [ 26 ], and/or through factors that characterize the Grinellian niche such as climate and habitat variables [ 27 ].…”