Large‐scale human effects on an arid African raptor community

Abstract

In the current scenario of biodiversity crisis there is a growing need for identifying causes of changes in biodiversity at large scales. Here we assess factors driving raptor community structure in the Sahel, a region suffering a wide range of environmental degradation and a vital area for European migrant birds. Using road surveys, we estimated the effects of population size, human settlement patterns (e.g. urban vs. nomadic) and land use on the raptor community, taking into account the major natural role played by productivity. Total raptor richness values were similar to those described for other steppe regions of the world, with one super-abundant migrant species, the black kite Milvus migrans; however, richness of resident raptors was strikingly lower than expected, with most large body-size African species (both eagles and vultures) absent. Raptor richness was strongly correlated with human activities in a scale-dependent fashion. At a 25 km resolution, raptor richness was driven by habitat and productivity, with a positive response to crops. At a smaller scale, human population was positively related with wintering species richness but negatively with richness of resident ones, perhaps as a consequence of non-agricultural activities such as direct harvesting and different forms of habitat degradation (e.g. overgrazing or firewood collection). Subsistence economies in systems with low natural environmental heterogeneity and with a human population over carrying capacity, such as the Sahel, may lead to exhausted biological systems even in the absence of intensive agricultural or urban land-use changes, as shown by the deeply impoverished sedentary raptor community. Our results suggest that, because habitat and productivity seem to play a relevant role in driving species richness, climate change may have a major effect on the raptor community of the Sahel.

Scavengers on the Move: Behavioural Changes in Foraging Search Patterns during the Annual Cycle

“…Interestingly, there are important differences in terms of landscape composition, climatic conditions and degree of human alteration between the European breeding grounds and the African wintering quarters [29], [37]. Food resources are sparsely distributed in the Sahel region, a transitional ecoregion between the Sahara desert and the southern tropical forest composed of semi-arid grasslands, savannahs, steppes, and thorn scrublands where traditional semi-nomad shepherds raise livestock in a system of transhumance [62].…”

“…Consequently, it is not surprising that under these conditions, Egyptian vultures chose a Brownian search strategy, thus maximizing encounter rate. Interestingly, what is remarkable is the high level of site-fidelity to wintering areas year after year [33], which can probably be related to previous knowledge of the region plus the relative homogeneity of the landscape across vast extensions [37], [62], thus substantially enhancing the vultures' ability to move in these familiar areas.…”

“…food) promotes changes in birds' behaviour, as a response to variations in environmental conditions between summering and wintering grounds [36] and between different habitats [3]. Taking into account human-induced habitat alterations and the rapid change in ecosystems management, mainly in developing countries [37], the study of the individual spatial response of migratory scavengers to changes in the distribution and availability of feeding resources during the annual cycle can help to improve our understanding about the optimal foraging strategy into a general dynamic context. To this end, using a GPS-based satellite-tracking dataset we specifically checked: i) the foraging strategies adopted by Egyptian vultures at the individual level; and ii) their variation during the annual cycle (i.e.…”

Scavenging in the Anthropocene: Human impact drives vertebrate scavenger species richness at a global scale

“…Similarly, we lack study sites on large extents of the tropical vegetation, deserts and boreal forests, so some particularities of these biomes may not be considered here. For example, there are large areas such as the Sahel, for instance, with light HFs (low road and infrastructure densities) but high human pressure on scavengers (Anadón, Sánchez-Zapata, Carrete, Donázar, & Hiraldo, 2010). Finally, it is also important to notice that most of the regions assessed in this study are located in human-dominated areas, and we lack sites from the most diverse regions in the planet.…”

Interspecific and intraspecific differences in habitat use and their conservation implications for Palaearctic harriers on Sahelian wintering grounds

“…2005), suggesting that the winter range of Eurasian raptors has been greatly impoverished. Counts along road transects indicate, however, that migratory raptors may have been less affected by expanding cultivation in the Sahel than Afrotropical species (Thiollay 2000, Anadón et al. 2010), although trends vary regionally and between species (Thiollay 2001, 2006, 2007), while long‐term comparisons are complicated by differences in rainfall patterns, which influence prey populations.…”