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Djomo Nana E.,Charles University | Djomo Nana E.,International Research and Training Center | Sedlacek O.,Charles University | Vokurkova J.,Charles University | Horak D.,Charles University
Ostrich | Year: 2014

Nest predation is the leading cause of reproductive failure in birds and thus it shapes their life history strategies. Intensities of nest predation appear to differ among nest locations and types in both temperate and tropical regions. However, there is limited knowledge of factors influencing susceptibility of avian nests to predation in Africa. The aim of our study was to investigate artificial nest predation rates of different ground and shrub nests located at different heights in the rainforest undergrowth. We placed artificial avian nests within a homogeneous lowland forest interior with sparse forest undergrowth in the Mount Cameroon National Park, Cameroon. We exposed three sets of nests: 50 bare-ground, 50 cup-ground and 50 cup-shrub nests, for 10 d. Predation was higher for cup-ground nests compared to cup-shrub nests, and bare-ground nests were more depredated than cup-ground nests. We concluded that the presence of a cup as well as higher nest position significantly increased probability of artificial nest survival. The results of this study suggest a potential selection pressure on nest type and placement in lowland forest birds for a poorly known tropical region. © 2014 Copyright NISC (Pty) Ltd.


Ferenc M.,Charles University | Fjeldsa J.,Copenhagen University | Sedlacek O.,Charles University | Motombi F.N.,Mount Cameroon National Park | And 4 more authors.
Oecologia | Year: 2016

The usual positive inter-specific relationship between range size and abundance of local populations can have notable exceptions in Afrotropical montane areas, where range-restricted bird species are unusually abundant. We tested how the area occupied locally by passerines and their geographic range size relate to local abundances along a tropical elevational gradient of Mt Cameroon, West-Central Africa. Data on bird assemblages were collected at six forested elevations (350, 650, 1100, 1500, 1850 m, 2200 m a.s.l.) using a standardised point count at 16 locations per elevation. Elevational ranges of birds were compiled from published sources and their geographic range sizes were determined as the occupancy of 1° x 1° grid cells. The observed relationship between local abundance and geographic range size within the entire passerine assemblage on Mt Cameroon disagrees with the most frequently reported positive pattern. However, the patterns differ among elevations, with positive trends of the abundance-range size relationship in lowland changing to negative trends towards higher elevations. Interestingly, the total assemblage abundances do not differ much among elevations and population size estimates of species occupying different parts of the gradient remain relatively constant. These patterns are caused by relatively high abundances of montane species, which might be a result of long-term ecological specialization and/or competitive release in species-poor montane locations and possibly facilitated by an extinction filter. Our data suggest that montane species’ abilities to maintain dense populations might compensate for less area available near mountain tops and help these populations to circumvent extinction. © 2016 Springer-Verlag Berlin Heidelberg


Sedlacek O.,Charles University | Vokurkova J.,Charles University | Ferenc M.,Charles University | Djomo E.N.,Charles University | And 4 more authors.
Ostrich | Year: 2015

Acoustic signals are frequently used for estimating avian species richness, abundance and community composition. However, sampling by traditional methods of bird surveys is often limited by availability of experienced researchers in the field, especially in the tropics. New bioacoustic approaches offer some solutions to such limitations and provide opportunities for more extensive spatial and temporal sampling. In our study, we compared results of traditional point counts with simultaneous acoustic samples obtained by automated soundscape recording units in the montane forest of Mount Cameroon. We showed that the estimates of species richness, abundance and community composition based on point counts and post-hoc laboratory listening to acoustic samples are very similar, especially for a distance limited up to 50 m. Species that were frequently missed during both point counts and listening to acoustic samples were typically those with relatively quiet songs. Abundances were rather underestimated by listening to acoustic samples in the most abundant species, including those occurring in flocks and species with low singing activity. Despite some possible biases, we demonstrated that the method based on listening to acoustic samples is relatively effective and offers a useful alternative approach for surveying Afromontane bird communities. © 2015 NISC (Pty) Ltd.


Nana E.D.,Charles University | Nana E.D.,International Research and Training Center | Munclinger P.,Charles University | Ferenc M.,Charles University | And 4 more authors.
African Zoology | Year: 2014

The western mountain greenbul, Andropadus tephrolaemus, is a poorly-known monomorphic forest greenbul. We investigated whether morphological measurements could be used to discriminate between sexes of this species, with a sample of birds captured in two forest types on Mt Cameroon. We used discriminant function analysis based on a combination of traits to develop models to discriminate between sexes. The sex of birds predicted from these models was compared with molecular sexing of the same individuals. Discriminant analysis revealed that a discriminant function incorporating wing length, tail length and bill height allowed 74% of western mountain greenbuls to be sexed correctly based on morphometric measurements alone. Sex ratios varied between montane and lowland forests, with the former having a higher proportion of males (70.5 and 54.6%, respectively), but the difference was not statistically significant. Cloacal sizes did not differ between males and females, and males do not develop large cloacal protuberances while breeding. This is in agreement with low predicted levels of sperm competition in this species. We show that sexing based on morphology has its limitations, but can still provide some insight if DNA analysis is not available.


Nana E.D.,Charles University | Nana E.D.,International Research and Training Center | Sedlacek O.,Charles University | Bayly N.,SELVA Investigacion Para la Conservacion en El Neotropico | And 6 more authors.
Biodiversity and Conservation | Year: 2014

The Cameroon volcanic line montane forests host specific avian assemblages with many endemic species. Such unique bird assemblages deserve adequate description for proper protection. For this purpose, we sampled birds in the upper montane forests of Mts Cameroon and Oku situated at ~2,250 m. We combined point counts and continuous observations to describe species composition and estimate densities of particular species. In total, we recorded 106 species; 45 only on Mt Oku, 21 only on Mt Cameroon, and 40 common to both mountains. The higher species richness on Mt Oku was due to non-forest species that invade the forest interior due to recent human disturbance. Endemic species of the Cameroon volcanic line and montane non-endemic species had higher abundances than widespread species in general. As a result, we did not find a positive abundance-range-size relationship for both locations. Our findings support a previously made observation that montane species of the Cameroon volcanic line have higher densities compared to widespread species. However, we also show that the structures of avian assemblages vary between sites as species spatial turnover was lower on Mt Cameroon than on Mt Oku and species common to both were more abundant on Mt Cameroon. This could be attributed to the more pristine forest on Mt Cameroon, with higher annual rainfall but also due to lower human impact and the existence of a continuous forest. Conservation action within the broader landscape context is thus necessary to secure diverse montane forests in West-Central Africa in the future. © 2014 Springer Science+Business Media Dordrecht.

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