Ondřej Sedláček

Comment on “High-resolution global maps of 21st-century forest cover change”

Hansen et al. (Reports, 15 November 2013, p. 850) published a high-resolution global forest map with detailed information on local forest loss and gain. We show that their product does not distinguish tropical forests from plantations and even herbaceous crops, which leads to a substantial underestimate of forest loss and compromises its value for local policy decisions.

Do Tengmalm’s Owls alter parental feeding effort under varying conditions of main prey availability?

We studied the diet composition and behavioural responses to variable food conditions in Tengmalm’s Owls (Aegolius funereus). The abundance of main prey (voles and mice) of owls was higher in the Ore Mountains, Czech Republic, than in the Kauhava region, Finland. We monitored nests continuously by a camera system to estimate the feeding frequency and to identify prey items provided to nestlings. We recorded 990 prey deliveries at six nests in the Ore Mountains and 1,679 prey deliveries at nine nests in the Kauhava region. Mice (Apodemus) and voles (Microtus and Clethrionomys) were the main foods of owls in the Ore Mountains, whereas voles (Clethrionomys and Microtus) and shrews (Sorex) were the main foods in the Kauhava region. In consequence, on average smaller prey items were brought to nestlings at the Finnish site. However, both absolute and relative (per one nestling) feeding frequency was higher in the Kauhava region, and the biomass available to individual nestlings did not differ between the two areas. Moreover, the Finnish and Czech pairs produced about the same number of fledglings. Our results suggest that male owls are able to maintain the amount of food required for chicks by switching to alternative prey, and to increase their prey delivery rates under conditions of reduced abundance of main food.

Sperm competition in tropical versus temperate zone birds

Sperm competition represents an important component of post-copulatory sexual selection. It has been argued that the level of sperm competition declines in birds towards the equator. However, to date, sperm competition estimates have been available mainly for avian species inhabiting the northern temperate zone. Here we apply a novel approach, using the coefficient of between-male variation (CVbm) in sperm size as an index for sperm competition risk, in a comparative analysis of 31 Afrotropical and 99 northern temperate zone passerine species. We found no difference in sperm competition risk between the two groups, nor any relationship with migration distance. However, a multivariate model indicated that sperm competition risk was highest in species with a combination of low body mass and few eggs per clutch. The effect of clutch size was most pronounced in tropical species, which indicates that sperm competition risk in tropical and temperate species is differently associated with particular life-history traits. Although tropical species had lower sperm competition risk than temperate zone species for overlapping clutch sizes, the idea of a generally reduced risk of sperm competition in tropical birds was not supported by our analysis.

A comparison of point counts with a new acoustic sampling method: a case study of a bird community from the montane forests of Mount Cameroon

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.

Geographic variation in avian clutch size and nest predation risk along a productivity gradient in South Africa

Geographic variation in avian clutch size is thought to be related to the variation in nest predation rate and food availability. We studied predation on artificial ground nests along a large-scale geographic gradient in South Africa characterised by increasing productivity from the deserts in the west to humid savannas in the east, and calculated mean clutch sizes of birds occurring in atlas quadrates surrounding our study sites. Clutch sizes generally increased with increasing productivity and seasonality. The least productive desert site was characterised also by the highest predation rate, whereas all the other sites located in savannas revealed much lower and more or less constant predation rate. We found no evidence for relationship between nest predation rates and clutch sizes of ground-nesting birds. This indicates that food availability is the major factor responsible for geographical variation in bird clutch sizes across South Africa, though high predation rate might also contribute to low clutch size in least productive arid environments.

Food niche differentiation in two syntopic sunbird species: a case study from the Cameroon Mountains

Closely related bird species can coexist in areas of range overlap due to differentiation of their ecological niches. If coexisting species have similar habitat requirements, separation of food niches presumably plays a crucial role. Theoretically, two possible food niche separation scenarios are possible: (1) use of different food resources or (2) temporal differences in feeding activity. We examined these mechanisms by investigating the feeding habits of two short-billed sunbirds (Cinnyris reichenowi and C. bouvieri) coexisting locally in the Bamenda Highlands, NW Cameroon. Daily feeding activity in both species showed a similar pattern, with two peaks (0800–0900 hours and 1500–1600 hours, respectively) and a prominent decrease in activity between 1100 and 1400 hours. However, the studied species clearly differed in their exploitation of plant resources. C. bouvieri mostly visited Lobelia columnaris, while C. reichenowi regularly visited three plant species, namely, Hypericum revolutum, Hypoestes aristata and Impatiens sakerana, with the most time spent at the second species. Such resource partitioning was probably caused by interspecific aggressive behaviour, since C. bouvieri actively repelled C. reichenowi from Lobelia columnaris plants, forcing C. reichenowi to feed on other plant species.ZusammenfassungNahe verwandte Vogelarten können in Gegenden, in denen sich ihre Vorkommen überschneiden, aufgrund einer Differenzierung ihrer ökologischen Nischen koexistieren. Falls koexistente Arten ähnliche Ansprüche an den Lebensraum aufweisen, kommt einer Trennung der Nahrungsnischen höchst wahrscheinlich die Schlüsselrolle zu. Theoretisch sind zwei mögliche Szenarien der Nahrungsnischentrennung denkbar: (1) die Nutzung unterschiedlicher Nahrungsressourcen, oder (2) zeitliche Unterschiede in der Nahrungsaufnahme-Aktivität. Wir erforschten diese Mechanismen indem wir die Ernährungsgewohnheiten zweier kurzschnäbliger Nektarvogelarten (Cinnyris reichenowi and C. bouvieri), die im Bamenda Hochland, Nordwestkamerun lokal gemeinsam vorkommen, untersuchten. Die tägliche Nahrungsaufnahme-Aktivität folgte bei beiden Arten einem ähnlichen Muster mit zwei Gipfeln (zwischen 08:00–09:00 bzw. 15:00–16:00 Uhr) und einem deutlichen Aktivitätsabfall zwischen 11:00 und 14:00 Uhr. Die beiden untersuchten Arten unterschieden sich aber klar in der Ausnutzung der Pflanzenressourcen. C. bouvieri besuchte überwiegend Lobelia columnaris, wohingegen C. reichenowi drei Pflanzenarten regelmäßig besuchte: Hypericum revolutum, Hypoestes aristata und Impatiens sakerana, dabei verbrachte sie an der zweiten Art die meiste Zeit. Diese Art der Ressourcenaufteilung hatte ihre Ursache wahrscheinlich in interspezifischem Aggressionsverhalten, da C. bouvieri und C. reichenowi aktiv von Pflanzen der Art Lobelia columnaris vertrieb und C. reichenowi dadurch zwang an anderen Pflanzenarten zu fressen.

Differences in the Nestling Diets of Sympatric Redstarts Phoenicurus phoenicurus and Black Redstarts P. ochruros: Species-Specific Preferences or Responses to Food Supply?

Abstract. We have investigated whether differences in nestling diet found between locally sympatric Redstarts and Black Redstarts are caused by species-specific preferences or by a different food supply in their territories. The diet of nestlings in a mosaic-like urban environment was studied using the neck-collar method. We found no significant difference in the length of Redstart and Black Redstart prey items. However, the two species did bring to their nestlings invertebrates of different taxa. We used the variance partitioning method based on multivariate Redundancy Analysis to test the influence of habitat, timing of breeding, and the species of redstart itself on nestling-diet composition. Most of the variance in the nestling diet (all the canonical axes explained 70.6% of the variance) could be attributed to habitat variables (34%) and the timing of breeding (8.9%), but only 8.1% to the species of redstart. We suggest that the diet of the two redstart species is influenced largely by current prey availability and, consequently, that interspecific competition is avoided primarily by territory exclusion rather than by food-niche separation. We consider the variance partitioning method to be a powerful tool for identifying the effects of various explanatory variables that could influence food composition in birds.

Evidence for an Edge Effect on Avian Nest Predation in Fragmented Afromontane Forests in the Bamenda-Banso Highlands, NW Cameroon

Habitat loss and fragmentation in tropical areas have long been presumed to reduce avian nesting success due to increased predation rates. Nevertheless, this prediction remains largely untested in tropical areas, because empirical data on the impacts of forest fragmentation on nest predation at both the landscape and patch scales in the tropics are still scarce, especially in West Africa. In this study, we examined the edge effects on nest predation rates in a large montane forest block and small forest fragments. Artificial nests used for our experiments mimicked the real nests of passerines confined to montane forest undergrowth in the Bamenda-Banso Highlands, the Northwest region of Cameroon, an endemic bird area of high conservation priority. We found equal overall predation rates in the landscape dominated by the large forest block as well as in the landscape consisting of small forest fragments, implying that the probability of nest failure was not significantly affected by habitat fragmentation on a landscape scale. However, predation rates were higher close to forest edges in the small forest remnants. Since such remnants represent the majority of local montane forests, this result suggests that the edge effect on bird nest predation may reduce nest survival and the population viability of many range-restricted bird species confined to the remaining natural habitats of the Bamenda-Banso Highlands.

Nest position and type affect predation rates of artificial avian nests in the tropical lowland forest on Mount Cameroon

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.

Signatures of diversifying selection and convergence acting on passerine Toll-like receptor 4 in an evolutionary context

Positive selection acting on Toll‐like receptors (TLRs) has been recently investigated to reveal evolutionary mechanisms of host–pathogen molecular co‐adaptation. Much of this research, however, has focused mainly on the identification of sites predicted to be under positive selection, bringing little insight into the functional differences and similarities among species and a limited understanding of convergent evolution in the innate immune molecules. In this study, we provide evidence of phenotypic variability in the avian TLR4 ligand‐binding region (LBR), the direct interface between host and pathogen molecular structures. We show that 55 passerine species vary substantially in the distribution of electrostatic potential on the surface of the receptor, and based on these distinct patterns, we identified four species clusters. Seven of the 34 evolutionarily nonconservative and positively selected residues correspond topologically to sites previously identified as being important for lipopolysaccharide, lipid IVa or MD‐2 binding. Five of these positions codetermine the identity of the charge clusters. Groups of species that host‐related communities of pathogens were predicted to cluster based on their TLR4 LBR charge. Despite some evidence for convergence among taxa, there were no clear associations between the TLR4 LBR charge distribution and any of the general ecological characteristics compared (migration, latitudinal distribution and diet). Closely related species, however, mostly belonged to the same surface charge cluster indicating that phylogenetic constraints are key determinants shaping TLR4 adaptive evolution. Our results suggest that host innate immune evolution is consistent with Fahrenholzs rule on the cospeciation of hosts and their parasites.