University of Groningen The role of breeding range, diet, mobility and body size in associations of raptor communities and land-use in a West African savanna Buij, Ralph; Croes, Barbara M.; Gort, Gerrit; Komdeur, Jan Published in: Biological Conservation DOI: 10.1016/j.biocon.2013.06.028 IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 2013 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Buij, R., Croes, B. M., Gort, G., & Komdeur, J. (2013). The role of breeding range, diet, mobility and body size in associations of raptor communities and land-use in a West African savanna. Biological Conservation, 166, 231-246. 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Download date: 11-02-2018 Biological Conservation 166 (2013) 231–246 Contents lists available at SciVerse ScienceDirect Biological Conservation journal homepage: www.elsevier.com/locate/biocon The role of breeding range, diet, mobility and body size in associations of raptor communities and land-use in a West African savanna ⇑ Ralph Buij a,b, , Barbara M. Croes b, Gerrit Gort c, Jan Komdeur a a Behavioural Ecology and Self-organization, Centre for Ecological and Evolutionary Studies, University of Groningen, Centre for Life Sciences, Nijenborgh 7, 9747 AG Groningen, The Netherlands b Institute of Environmental Sciences, Leiden University, Einsteinweg 2, 2300 RA Leiden, The Netherlands c Biometris, Wageningen University, PO Box 100, 6700 AC Wageningen, The Netherlands article info abstract Article history: To provide insight into raptor declines in western Africa, we investigated associations between land-use Received 2 August 2012 and raptor distribution patterns in Cameroon. We examined the role of breeding distribution, species’ Received in revised form 18 June 2013 migratory mobility, diet, body size, and thus area requirements, on 5-km scale patterns of raptor richness Accepted 21 June 2013 and abundance. We recorded 15,661 individuals, comprising 55 species during road surveys, spanning four annual cycles. Results revealed evidence for the importance of National Parks (N.P.’s), natural vege- tation, humans, and cotton in shaping raptor assemblages, but responses differed between functional Keywords: groups and biogeographical zones. Human populations and natural habitat, interacting with zone, were Raptor functional groups important predictors of Afrotropical raptor richness, and N.P.’s of Palearctic raptor richness. Areas cleared Land-use change Natural habitat of natural habitat in the Guinea zone had comparatively rich and abundant large, small sedentary and Human populations migratory Afrotropical raptor assemblages, but humans limited positive effects. Palearctic raptor abun- Cotton dance peaked at higher levels of human land-use than Afrotropical raptors. Vertebrate-hunting Palearctic Palearctic and Afrotropical raptors raptor richness was positively associated with cropland, while cotton and human land-use in the Inun- Cameroon dation zone had a stronger negative impact on insectivorous Palearctic raptors. Richness of large seden- tary raptors declined with increasing distance to N.P.’s, contrary to communal scavenger richness, which increased with human populations. Humans, habitat loss and cotton in the Inundation and Sudan zones had similar, negative effects on small sedentary and small migratory Afrotropical raptor assemblages. We conclude that increasing human populations, natural vegetation loss, and expanding cotton will nega- tively affect the majority of Afrotropical and insectivorous Palearctic raptors, while vertebrate-hunting Palearctic raptors may benefit from cropland expansion. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction stitute the last refuges for the most threatened species, West Africa’s protected areas are often small and inadequately protected In Africa, rapid human population growth drives overexploita- (Brashares et al., 2001; Newmark, 2008). Consequently, the long- tion of the land and is a major cause of past, present and future bio- term persistence of many species of indigenous plants and animals diversity loss (Biggs et al., 2008), reflected by a decrease in species is highly dependent on land-use in the human-dominated land- richness as land-use is increasingly dominated by human activities scapes and on their capacity to survive within these (Benton (Homewood et al., 2001; Sinclair et al., 2002; Söderström et al., et al., 2003; Martin et al., 2007). 2003; Blaum et al., 2007). Compared to the rest of the continent, One of the most dramatic illustrations of the loss of diversity in West Africa’s biodiversity stands out for being most severely threa- West African savannas is the widespread impoverishment of its tened (Newmark, 2008; Craigie et al., 2010). This was attributed to raptor populations during the past 40 years (Thiollay, 2006a,c, human population densities and rates of habitat conversion, which 2007b). Raptor population declines in Africa have been linked to have been higher in West Africa’s sub-Sahelian savannas than else- disturbance of nests and persecution by humans (Virani and Har- where on the continent (Brink and Eva, 2009). Although they con- per, 2009; Bamford et al., 2009), loss of woodland and nest sites due to firewood cutting, expanding and intensifying cultivation, ⇑ Corresponding author at: Behavioural Ecology and Self-organization, Centre for with increased pesticide use (Thiollay, 2001, 2006a,c, 2007b), and Ecological and Evolutionary Studies, University of Groningen, Centre for Life overgrazing (which depresses important prey resources; Sciences, Nijenborgh 7, 9747 AG Groningen, The Netherlands. Mobile: +31 6 Herremans and Herremans-Tonnoeyr, 2000). Despite high human 40466362. population densities on a continental scale, not all raptor species E-mail address: [email protected] (R. Buij). 0006-3207/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biocon.2013.06.028 232 R. Buij et al. / Biological Conservation 166 (2013) 231–246 in West Africa declined sharply, few apparently remaining stable 2. Methods (Thiollay, 2001, 2006a), pointing to variation in species-specific re- sponse to environmental alteration. Afrotropical raptors, defined 2.1. Study area here as the assemblage of sedentary, nomadic, and intra-African migratory raptors breeding in sub-Saharan Africa (Thiollay, 1977, Surveys of diurnal raptors (order Falconiformes) along roads 1989), depend on West African savannas during the greater part were conducted in the Far North Province, North Province and of their annual cycle, including breeding and non-breeding sea- Adamawa Province of Cameroon (7°120N–12°050N and 13°0E– sons. Consequently, their vulnerability to land-use changes is likely 15°100E; Fig. 1). The climate is semi-arid, with rains occurring be- to be greater than that of more mobile Palearctic raptors, the tween April and October, peaking between June and September in majority of which visit the region for several months during the the north and between May and October in the south. A cool dry non-breeding season. Among Palearctic raptors, those that feed season (November–January) precedes a hot season (February– on vertebrates may even have profited from expanding sorghum May) during which the first rains occur (several weeks earlier and rice cultivation with seasonally-abundant diurnal rodents and ending later in the southern part of the study area). Mean (Buij et al., 2012; Buij and Croes, 2013), while granivorous birds annual temperature is 24–28 °C and peaks in March–May when seasonally attracted to small-grain cereal crops (Dyer and Ward, temperatures of 47 °C are reached in the north. 1977; Elliott, 1989) constitute another major food source (Thiollay, Road surveys covered three biogeographical zones, which are 1989). Conversely, the bulk of the food for primarily insectivorous representative of three main savanna types between the 450 and Palearctic raptors in West African savannas (medium- and large- 1600 isohyets in western Africa (White, 1983), differing in produc- bodied grasshoppers) are most common in mosaics of fallow, crop- tivity and vegetation composition (Fig. 1). Zone 1. Sudano-Sahelian fields, and deforested land, or productive grasslands, rather than Inundation zone. Located at the transition of the Sahel and the Su- large-scale or intensive cultivation, although croplands may be- dan climatic zones (rainfall: 450–700 mm/annum) in the southern come heavily infested particularly during acridid outbreaks (Mullié part of the Lake Chad Basin. The vegetation consists of partly- and Guèye, 2010). Like most insectivorous Palearctic raptors, flooded grasslands with communities of Acacia