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The effect of forest fragmentation on mixed-species foraging bird flocks has been poorly evaluated, particularly in African forests. We examined the consequences of forest fragmentation on such flocks in the East Usambara Mountains, Tanzania, by addressing ecological as well as behavioral components. We counted these flocks in five small (<31 ha), isolated fragments and six widely spaced continuous forest sites. Given that flock cohesion and stability might be facilitated via positive interactions of leader or nuclear species, we focused on one putative nuclear species, the square-tailed drongo ( Dicrurus ludwigii ), and using playback of its vocalisations, we evaluated (i) if its vocalisations attracted flocking birds as expected by a nuclear species, and (ii) if loss of this species in fragments contributed to flock declines. We found that flocks in forest fragments had smaller sizes, reduced species richness, a reduced proportion of understorey specialists, a higher proportion of forest generalists and non-forest species, and were more variable in size and composition compared to flocks observed in continuous forest. Furthermore, flocks in fragments were composed of a higher proportion of omnivores than insectivores. Despite lower absolute abundance in fragments, D. ludwigii was observed in 86% of natural occurring flocks in both fragments and continuous forest, and flocks with D. ludwigii were significantly larger than those without it––especially in the continuous forest. Playback vocalisations of D . ludwigii attracted flocks of similar abundance and species richness in fragments and continuous forest, but a vastly different composition, confirming (i) its nuclear role and (ii) that, in fragments, flock assemblages had a distinct composition, with a high proportion of forest generalists and non-forest species. Loss or diminished abundance of nuclear species due to fragmentation may be an important factor that affects the presence and composition of mixed-species flocks. Given that 67% of flocking species forage in the understorey, and that insectivores were more negatively affected in fragments than omnivores, the implications of our findings are relevant for conservation in tropical forests. [ABSTRACT FROM AUTHOR]

Avian insectivores of the tropical rainforest understory (“understory insectivores”) are common, diverse, and often sensitive to disturbance of tropical forest, making them useful as sentinels of rainforest ecosystem change. At the 2013 joint American Ornithologists’ Union and Cooper Ornithological Society meeting in Chicago, USA, researchers convened a symposium to address the ecology and conservation of understory insectivores. This Special Issue of Biological Conservation is the result of that symposium: a collection of articles that unites our efforts to further understand and conserve understory insectivores. In this introductory paper, we review the diversity and ecology of understory insectivores, identify threats to the guild, discuss hypotheses on drivers of population declines, and make suggestions for future research. Deforestation and forest degradation are the immediate threats to this guild, with agricultural expansion (particularly oil palm plantations), urbanization, road expansion and logging leading the list. Although vulnerabilities of this guild are most evident in the Neotropics, there are few studies from Asia and fewer still from Africa—we recommend increased geographic coverage. If we are to understand the vulnerabilities of understory insectivores from a pantropical perspective, researchers should prioritize understanding the most serious threats (e.g., edge effects, deforestation, fragmentation, etc.) and standardize efforts to gauge understory insectivores’ response to these threats (e.g., via species richness, abundance, demographic metrics). A coordinated approach by researchers working in tropical rainforests across the globe can help us understand the ecology of understory insectivores and meaningfully apply conservation and management actions. [ABSTRACT FROM AUTHOR]

Abstract: This paper explores whether spatial variation in the biodiversity values of vertebrates and plants (species richness, range-size rarity and number or proportion of IUCN Red Listed threatened species) of three African tropical mountain ranges (Eastern Arc, Albertine Rift and Cameroon-Nigeria mountains within the Biafran Forests and Highlands) co-vary with proxy measures of threat (human population density and human infrastructure). We find that species richness, range-size rarity, and threatened species scores are all significantly higher in these three tropical African mountain ranges than across the rest of sub-Saharan Africa. When compared with the rest of sub-Saharan Africa, human population density is only significantly higher in the Albertine Rift mountains, whereas human infrastructure is only significantly higher in the Albertine Rift and the Cameroon-Nigeria mountains. Statistically there are strong positive correlations between human density and species richness, endemism and density or proportion of threatened species across the three tropical African mountain ranges, and all of sub-Saharan Africa. Kendall partial rank-order correlation shows that across the African tropical mountains human population density, but not human infrastructure, best correlates with biodiversity values. This is not the case across all of sub-Saharan Africa where human density and human infrastructure both correlate almost equally well with biodiversity values. The primary conservation challenge in the African tropical mountains is a fairly dense and poor rural population that is reliant on farming for their livelihood. Conservation strategies have to address agricultural production and expansion, in some cases across the boundaries and into existing reserves. Strategies also have to maintain, or finalise, an adequate protected area network. Such strategies cannot be implemented in conflict with the local population, but have to find ways to provide benefits to the people living adjacent to the remaining forested areas, in return for their assistance in conserving the forest habitats, their biodiversity, and their ecosystem functions. [Copyright &y& Elsevier]