A baseline estimate of population size for monitoring the Endangered Madagascar giant jumping rat Hypogeomys antimena R ichard P. Young,Anselme T oto V olahy,Robert B ourou,Richard L ewis, J oanna D urbin,Tim J. Wright,Tim D. Hounsome and J ohn E. Fa Abstract The Endangered Madagascar giant jumping rat, Introduction Hypogeomys antimena, has suffered a major decline in dis- tribution and is now restricted to two seemingly uncon- eciduous, seasonally dry forest in western Madagascar nected sub-populations in the largest remaining fragment of Dharbours high numbers of animal and plant endemics deciduous, seasonally dry forest in Menabe, western Mada- but has been dramatically reduced in extent and become gascar. In a previous study a rapid decrease in numbers of highly fragmented through encroachment by subsistence H. antimena was observed in relatively intact forest, suggest- agriculture and timber harvesting. This habitat is now ing a factor of population decline additional to habitat loss, one of the highest conservation priorities in Madagascar 2001 and provoking fears of a negative trend occurring across its (Ganzhorn et al., ). Dry forest once covered much of 1990 3 remaining range. In the current study we conducted exten- western Madagascar but by only an estimated c. %of 1997 sive line transect surveys to estimate active H. antimena the original cover remained (Smith, ). As a result, many burrow density in 2004 and 2005 as an index of population species associated with this habitat have suffered concom- size, and trapping to estimate mean group size, as a multiplier itant declines in their distribution and population size and for population size estimation. Within the surveyed areas we are now lost or threatened with extinction. estimated the combined size of the two H. antimena sub- The Menabe region of central western Madagascar, populations in 2005 to be c. 36,000, considerably larger than between the Tsiribihina and Tomitsy rivers, contains one previously assumed. There was no evidence that active of the largest remaining tracts of deciduous dry forest. Until burrow density across the species’ known range changed recently the Menabe forest was largely unprotected and over 1995 2000 4 between 2000 and 2005. H. antimena was not uniformly – c. % was being lost per annum through clear- distributed, with higher densities of active burrows found in felling and burning, or was heavily degraded through human forest with the highest canopy in areas furthest from forest disturbance, including timber extraction (Sommer et al., 2002 2000 edges. These core forest areas are vital for the species’ ). However, since , local and international conser- conservation and the recent declaration that the Menabe vation partners have intensified measures to arrest defores- 2006 forest will receive statutory protection provides hope that tation. In the forest was given protected area status H. antimena may be safeguarded. However, given its re- by the Madagascar Government as a move towards imple- stricted range and low reproductive output, among other menting a long-term management plan for biodiversity con- factors, H. antimena remains threatened and requires close servation and sustainable use of the area’s natural resources. future monitoring. The Madagascar giant jumping rat Hypogeomys antimena is a large rodent, endemic to the Menabe forest (Cook et al., Keywords Distance sampling, dry forest, habitat fragmen- 1991) and considered a flagship species for the dry forest tation, Madagascar, population monitoring, status survey. habitat. It has probably one of the most restricted ranges of any Malagasy mammal (Goodman & Rakotondravony, 1996) and is categorized as Endangered on the IUCN Red List (IUCN, 2007). The extent of occurrence of the species was estimated to have declined by 52%over1985–2000 RICHARD P. YOUNG* (Corresponding author), TIM J. WRIGHT and JOHN E. 2002 FA Durrell Wildlife Conservation Trust, Les Augre`sManor,Trinity, (Sommer et al., )andH. antimena is now thought to be Jersey, JE3 5BP, UK Channel Islands. E-mail [email protected] limited to two of the least modified blocks of the Menabe ANSELME TOTO VOLAHY, ROBERT BOUROU, RICHARD LEWIS and JOANNA forest, known as the Kirindy/CFPF and Ambadira forests, 2 DURBIN Durrell Wildlife Conservation Trust-Madagascar, BP8511, which are c. 200 km in area (Sommer & Tichy, 1999; Antananarivo 101, Madagascar. Sommer & Hommen, 2000). A global H. antimena pop- TIM D. HOUNSOME Biocensus, 3 All Saints Fields, Summer Street, Stroud, 9 000 2000 2001 Gloucestershire, GL5 1NE, UK. ulation of c. , adults was estimated from a – survey (Sommer et al., 2002). Based on these data a pop- *Also at: Department of Biology & Biochemistry, University of Bath, Bath, BA2 7AY, UK. ulation viability analysis predicted that if past deforestation Received 25 April 2007. Revision requested 11 June 2007. rates continue the species would become extinct within Accepted 30 August 2007. 24 years (Sommer et al., 2002). ª 2008 Fauna & Flora International, Oryx, 42(4), 584–591 doi:10.1017/S0030605307000816 Printed in the United Kingdom Downloaded from https://www.cambridge.org/core. IP address: 170.106.202.58, on 24 Sep 2021 at 22:11:49, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0030605307000816 Monitoring giant jumping rats 585 Observations from an intensive study of H. antimena in distribution information, we delineated areas of potentially the Kirindy/CFPF forest suggested that the species may be suitable habitat. We estimated there is 17,202 ha of poten- declining even in relatively undisturbed forest (Sommer & tially suitable habitat in the Ambadira forest and 15,599 ha Hommen, 2000). Between 1992 and 2000 the study pop- in Kirindy/CFPF forest, and these areas of forest were ulation fell by c. 55% (Sommer & Hommen, 2000). Because defined, for the purposes of this study, as the northern and H. antimena is an obligate monogamous species, with a low southern survey areas respectively (Fig. 1). Because of a lack reproductive output of 1–2 offspring per year (Sommer, of field data during the design phase the delineation of the 2001), these declines were perceived not as part of a pop- survey areas was subjective, and therefore it is possible that ulation cycle but of a long-term negative trend that may be we did not cover the entire range of H. antimena. occurring across its range (Sommer & Hommen, 2000). The main proposed explanation was predation by domestic Methods dogs belonging to tenrec (Tenrecidae) hunters (Sommer & 2000 Hommen, ), although disease was also suspected. Estimation of active burrow density However, the decline reported in H. antimena (Sommer et al., 2002) was largely based on one study site, and may H. antimena live together as adult pairs with one or two not therefore be representative of the entire population. young, and use underground burrows to rest during the day To determine more accurately the current size of the and to avoid predation (Cook et al., 1991). Regularly used H. antimena population and any short-term trends, we burrows (hereafter referred to as active) are clearly identifi- carried out extensive line transect surveys across its known able from inactive ones by the presence of recently dug soil range in 2004 and 2005.Wepresenttheresultsofgener- and often by the absence of leaves, twigs or cobwebs in the alized linear models to assess the relationship between general burrow entrance. Recently dug soil is distinctive as it differs habitat characteristics and the distribution and numbers of in colour and structure to the surface soil. An intensive the species. We also make recommendations for the design mark-recapture study (Sommer & Hommen, 2000)in- of an ongoing monitoring programme for H. antimena. dicated that family groups use only one burrow for exten- sive periods of time, and thus the density of active burrows Study area can be used as an index of population size of H. antimena (Sommer et al., 2002). The deciduous dry forests of Menabe are characterized by A plot sampling survey of active burrows was previously the presence of baobab trees (Adansonia spp.) and occur carried out during April–November in 2000 and 2001 2 primarily on sandy and lateritic soils. The region’s climate is (Sommer et al., 2002). Each plot was 1 km in area and dominated by a dry season (April–November), with a hot, was surveyed by teams of five people walking systematically wet season in the intervening period. Average total annual across the plot and counting and marking all active and rainfall is c. 800 mm (Sorg & Rohner, 1996). inactive burrows observed (as active burrows are relatively H. antimena is thought to occur in two sub-populations, easily detected in the forest during the dry season it was one each in the two main blocks of the Menabe forest, the considered likely that few were missed). Four and six plots Ambadira forest in the north and the Kirindy/CFPF forest were surveyed in the northern and southern study areas, in the south (Sommer & Tichy, 1999; Fig. 1). From surveys respectively. Full details of the survey design and data conducted by Sommer et al. (2002)in2000, the northern collection protocols are provided in Sommer et al. (2002). and southern sub-populations were estimated to be dis- Seven of these 10 plots fell within the area of the 2004–2005 tributed over c. 4,000 and 15,000 ha, respectively, of suitable survey and these data were used to estimate retrospectively habitat. These surveys revealed that H. antimena had mean active burrow density for 2000–2001. The remaining probably disappeared from dry forest to the west of the three plots, in which no active burrows were recorded in main road that runs south to north through the Menabe 2000–2001, fell outside the 2004–2005 survey area and were region, and from the forest corridor that connects the therefore not included in the present analysis.