Mekonnen Et Al 2012
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American Journal of Primatology 00:1–10 (2012) RESEARCH ARTICLE Newly Discovered Bale Monkey Populations in Forest Fragments in Southern Ethiopia: Evidence of Crop Raiding, Hybridization With Grivets, and Other Conservation Threats ADDISU MEKONNEN1∗, AFEWORK BEKELE1, PETER J. FASHING2, JEAN-MARC LERNOULD3, ANAGAW ATICKEM4, AND NILS CHR. STENSETH4 1Zoological Sciences Program Unit, Faculty of Life Sciences, Addis Ababa University, Addis Ababa, Ethiopia 2Department of Anthropology and Environmental Studies Program, California State University Fullerton, Fullerton, California 3Conservation des Esp`eces et des Populations Animales (CEPA), Schlierbach, France 4Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biology, University of Oslo, Blindern, Oslo Norway Until recently, the Bale monkey (Chlorocebus djamdjamensis), an arboreal primate endemic to the southern Ethiopian highlands, remained virtually unstudied, and its distribution pattern inadequately documented. To broaden our knowledge of the species’ distribution and abundance, we carried out interviews with local people and total count surveys for Bale monkeys across 67 fragmented forest sites in human-dominated landscapes in the Oromia and Southern Nations, Nationalities, and People’s Regions, Ethiopia. From January 2010 to May 2011, we discovered 26 new Bale monkey populations inhabiting forest fragments at elevations ranging from 2,355 to 3,204 m asl. Across these populations, we recorded 37 groups ranging in size from 9 to 29 individuals (Mean = 19.5, SD = 4.5), for a total of 722 individuals. Black-and-white colobus monkeys (Colobus guereza) were sympatric with Bale monkeys at all sites, while grivet monkeys (Chlorocebus aethiops) were found only at sites where Bale monkeys did not occur. All of the newly discovered Bale monkey sites once contained bamboo forest, though at 35% of the sites bamboo forest had been eliminated during the past two decades. The persistence of Bale monkeys at fragmented sites lacking bamboo suggests greater habitat flexibility for the species than previously thought, though the long-term viability of populations both with and without bamboo remains uncertain. Human hunting in response to crop raiding, a behavior the monkeys engaged in at all sites, represents a major threat facing the newly discovered Bale monkey populations. Furthermore, despite their current lack of sympatry, apparently hybrid individuals between Bale monkeys and grivets were noted at three sites, posing yet another potential obstacle to Bale monkey conservation. Community conservation programs aimed at (1) protecting remaining habitat fragments, (2) planting bamboo and trees within and between fragments, and (3) reducing crop raiding represent the only hope for survival of the newly discovered Bale monkey populations. Am. J. Primatol. 00:1–10, 2012. C 2012 Wiley Periodicals, Inc. Key words: Chlorocebus djamdjamensis; conservation; crop raiding; distribution; forest fragmen- tation; hybridization INTRODUCTION for conflict between hungry primates and peo- Nonhuman primates face a variety of an- ple [Campbell-Smith et al., 2010; Cowlishaw and thropogenic threats including habitat destruction, Contract grant sponsor: Conservation des Especes` et des Pop- hunting, infectious disease, and climate change ulations Animals (CEPA); contract grant sponsor: Zoologis- [Chapman et al., 2006; IUCN, 2010]. The most se- che Gesellschaft fur¨ Arten- und Populationsschutz, Germany (ZGAP); contract grant sponsor: Le Conservatoire pour la Protec- rious immediate threat to the survival of many tion des Primates; contract grant sponsor: La Vallee´ des Singes primate species is habitat destruction for timber, Primate Park. ∗ agricultural land, and human settlement [Isabirye- Correspondence to: Addisu Mekonnen, Zoological Sciences Pro- Basuta & Lwanga, 2008; IUCN, 2010]. Habitat loss gram Unit, Faculty of Life Sciences, Addis Ababa University, PO has forced many primate populations to live in small Box 1176, Addis Ababa, Ethiopia. E-mail: [email protected] fragments isolated from one another by human- Received 25 August 2011; revised 17 November 2011; revision accepted 19 November 2011 dominated landscapes [Marsh, 2003]. Conversion of primate habitats into agricul- DOI 10.1002/ajp.21999 Published online xx XXXX xxxx in Wiley Online Library tural land, in particular, creates the potential (wileyonlinelibrary.com). C 2012 Wiley Periodicals, Inc. 2 / Mekonnen et al. Dunbar, 2000; Oates, 1996]. Crop raiding is an lion to 74 million. The resulting increasing human increasing source of human-wildlife conflict and demand for natural resources in Ethiopia has led many primate species living adjacent to agricul- to an alarming rate of deforestation. While initially tural land are known to engage in this behavior possessing 40% forest cover, the most recent esti- [Campbell-Smith et al., 2010; Hill, 1997; Lee & Pris- mates suggest that only 2.4% of Ethiopia remains ton, 2005; Marchal & Hill, 2009; Priston & Under- forested today [FDRE, 1998; Waktola, 1999]. Most down, 2009; Warren, 2008]. Local communities are of this forest clearance has been carried out to facil- likely to develop negative attitudes towards primate itate shifting agriculture, fuel wood collection, and species that crop raid, thereby further endanger- livestock production [FDRE, 1998; Waktola, 1999]. ing primates already at risk because of human en- From January 2010 to May 2011, we carried out croachment upon their habitat [Campbell-Smith et surveys to (1) improve our knowledge of the distri- al., 2010; Hill, 1997]. bution and abundance of Bale monkeys across the Habitat disturbance may also result in increased southern Ethiopian highlands and (2) document the chance of hybridization between taxa. For example, conservation threats the species faces because of the species previously separated by large tracts of for- degradation and loss of its habitat. Prior to our sur- est may encounter one another in agricultural areas veys, Bale monkeys were known primarily from sev- once forest has been cleared, leading to hybridization eral sites in and around Bale Mountains National [Chapman & Chapman, 1996; Detwiler et al., 2005]. Park in the Bale Mountains, Oromia Region (Fig. 1). Unfortunately, the conservation threats posed to pri- Here, we report the presence of newly discovered mate species by hybridization remain relatively lit- Bale monkey populations at 26 localities consisting tle studied [though see the excellent recent review of of forest fragments far to the W and SW of most pre- what is known on the topic by Detwiler et al., 2005]. viously known populations. At all 26 localities, Bale Species with limited distributions and narrow monkeys were directly observed or reported by lo- ecological niches are especially susceptible to extinc- cal people to engage in crop raiding. Furthermore, at tion caused by habitat disturbance [Yu & Dobson, three additional localities we recorded the presence 2000; Harcourt, 2006]. For example, the Bale mon- of likely hybrids between Bale monkeys (C. djamd- key (Chlorocebus djamdjamensis), an arboreal pri- jamensis) and grivet monkeys (C. aethiops). We sug- mate endemic to the southern Ethiopian highlands, gest strategies for conserving fragmented Bale mon- is at risk of extinction (IUCN classification: Vulner- key populations and expect that the new information able) because of rapid clearance of its bamboo for- on Bale monkey distribution, abundance, and con- est habitat [Butynski et al., 2008; Mekonnen et al., servation threats presented here will prove helpful 2010a]. While the full extent of the Bale monkey’s in updating the categorization of the species on the distribution remains unknown, its apparent dietary IUCN Red List. specialization on bamboo [Mekonnen et al., 2010a] suggests the species may lack the ecological flexi- bility to cope with disturbance to its habitat. Fur- METHODS thermore, Kingdon [1997] suggested that hybridiza- From January to June 2010 and December 2010 tion of Bale monkeys (C. djamdjamensis)withother to May 2011, Addisu Mekonnen and a team of more widespread and adaptable Chlorocebus spp. trained field assistants carried out surveys in 67 for- [e.g., grivets (Chlorocebus aethiops)orvervets(C. est fragments separated from one another by at least pygerythrus)] represents a potential threat facing 1 km of cultivated land and human settlement in two the species as its habitat is cleared for agricultural neighboring administrative regions, Oromia Region purposes. While the Bale monkey is unique among (West Arsi and Guji Zones) and Southern Nations, Chlorocebus spp. in its specialization on bamboo and Nationalities, and People’s (SNNP) Region (Sidama mostly arboreal lifestyle [Mekonnen et al., 2010a], and Gedeo Zones) (Fig. 1). We identified areas to sur- destruction of its habitat for agriculture could lead vey as those presently (or until recently) containing to crop raiding and spatial overlap and hybridiza- at least some bamboo and occurring at elevations tion with other more terrestrial Chlorocebus taxa. ranging from 2,000 to 3,300 m asl (i.e., the approxi- Indeed, J.-M. Lernould [pers. obs.] (who kept a tame mate range of elevations at which Bale monkeys are young male Bale monkey at home in Goba, Ethiopia known to occur). These areas generally consisted of at a time when the species was only known from some combination of bamboo-dominated forest, tree- the holotype) noted possible Bale monkey × grivet dominated forest, cultivated land, and human set- hybrids