Mammalia 2017; aop
Short Note Andrew M. Kittle* and Anjali C. Watson
Density of leopards (Panthera pardus kotiya) in Horton Plains National Park in the Central Highlands of Sri Lanka DOI 10.1515/mammalia-2016-0139 Received September 20, 2016; accepted March 29, 2017
Abstract: Quantitative ecological data needs to inform management of the endangered, endemic Sri Lankan leopard. Estimating habitat-specific leopard density and prey availability provides important baselines and improved understanding of the island-wide population. We used remote cameras in a spatially explicit capture-recapture framework to estimate leopard density (11.7 adult individuals/100 km2) and distance sampling to estimate prey density, within Horton Plains National Park. Sambar density was 178/km2 within the central grasslands, which represent a spatially anchored resource for sambar and in turn, a highly clumped, abundant resource for leopards. This study represents the first robust estimate of leopard density in Sri Lanka’s montane zone. Keywords: camera traps; density; leopard; spatially explicit capture recapture; Sri Lanka. The Sri Lankan leopard (Panthera pardus kotiya, Deraniyagala 1956) is an endemic sub-species currently listed as endangered by the International Union for the Conservation of Nature (Kittle and Watson 2015, IUCN 2016). It has been Sri Lanka’s top predator since the island separated from the Indian sub-continent ~5000– 10,000 ybp (Deraniyagala 1992, Yokoyama et al. 2000, Manamendra-Arachchi et al. 2005), with this extended absence of dominant intra-guild competition unique for the species (Turner 1997). A recent review of the global status and distribution of leopards and research effort expended across their range, indicated that five of the nine recognized sub-species (Miththapala et al. 1996,
*Corresponding author: Andrew M. Kittle, The Wilderness and Wildlife Conservation Trust, 130 Reid Avenue, Colombo 04, Sri Lanka, e-mail:
[email protected] Anjali C. Watson: The Wilderness and Wildlife Conservation Trust, 130 Reid Avenue, Colombo 04, Sri Lanka
Uphyrkina et al. 2001), including the Sri Lankan leopard, were particularly threatened due to their occupation of few, typically small and isolated, forest patches (Jacobson et al. 2016). Research effort was perceived to be inversely correlated with threat level, with the data deficiency most acute for those sub-species in greatest need of urgent attention (Jacobson et al. 2016). In Sri Lanka, recent research has revealed the leopard as extant across much of the island including arid and dry lowlands and pockets of the lowland wet zone extending into the sub-montane and montane forests of the central hills (Watson and Kittle 2004, Kittle et al. 2012, Jacobson et al. 2016). Given this wide distribution, this apex carnivore has the potential to exert profound influence on the structure and composition of Sri Lanka’s varied ecosystems (Ripple et al. 2014). Furthermore, on a 65,610 km2 island which is home to >20 million people (density 332/km2; Department of Census and Statistics 2012), the potential for wide ranging top predators to interact with the expanding human population puts these species at greater risk (Inskip and Zimmerman 2009). As such, it is important to develop a more complete understanding of leopard ecology and behavior in Sri Lanka to preserve both its ecological role in the system and mitigate potential conflicts arising through interactions between humans and leopards (Jacobson et al. 2016). Few published leopard abundance estimates exist for Sri Lanka, with those that do based on incidental daytime observations in protected areas in the island’s dry (Eisenberg and Lockhart 1972) and arid zone (Santiapillai et al. 1982, DeSilva and Jayaratne 1994). A recent spatially explicit capture-recapture density estimate from the Ruhuna (Yala) National Park in the south-eastern arid zone suggests Sri Lankan leopard density varies in accordance with prey availability (Kittle et al. 2017), a pattern previously suggested for leopards in Sri Lanka (Eisenberg and Lockhart 1972, DeSilva and Jayaratne 1994), documented for leopards more widely (Marker and Dickman 2005) and broadly observed for carnivores globally (Carbone and Gittleman 2002). Assessing leopard densities and
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2 A.M. Kittle and A.C. Watson: Sri Lankan leopard density in Horton Plains determining prey abundance in other regions of the island is necessary to gain a more nuanced appreciation of the ecology and therefore, conservation and management requirements, of this apex predator. Furthermore, this can provide a baseline for future reference and is a useful way to increase the precision of island-wide leopard status assessments (Santiapillai 1986, Kittle and Watson 2008, 2015). We used remote cameras (Trailmaster TM1550, Goodson and Associates, Lenexa, KS, USA) in a capturerecapture framework to estimate the leopard population in Horton Plains National Park (HPNP). HPNP is a 3160 hectare protected area (PA) and World Heritage Site on the southern plateau of the island’s central hills which ranges in elevation from 1200 to 2300 m (Figure 1). It is characterized by rugged mountains swathed in dense montane forest and interspersed with large open grasslands through which course numerous streams. The Park is bordered to the north-west, east and south by tea estates and on the west by contiguous forest in the form of the Bogawanthalawa and Agra-Bopats forest reserves. Rainfall is high (>2000 mm annually) and frequent mist has allowed the establishment of Sri Lanka’s largest tract of cloud forests in the upper reaches of the PA (Green 1990). This small park is of great importance given that
it encompasses the island’s 2nd and 3rd highest peaks – Kirigalpoththa (2389 m) and Thotupola Kanda (2357 m) – as well as the headwaters of three of Sri Lanka’s largest rivers, the Mahaweli, Kelani and Walawe. The leopard population within this PA has never been quantitatively assessed. Potential prey available to leopards in HPNP include Rattus species, porcupine (Hystrix indica, Kerr 1792), blacknaped hare (Lepus nigricolis, Cuvier 1823), yellow-striped chevrotain (Moschiola kathygre, Groves and Meijaard 2005), Indian muntjac (Muntiacus muntjak, Rafinesque 1815), purple faced langur (Trachypithecus vetulus monticola, Erxleben 1777) and sambar (Rusa unicolor, Kerr 1792). Sambar are abundant in HPNP, congregating in large herds in the open grasslands. Using line transects, sambar crude density has been estimated as 66.5/km2 and ecological density as 223.5/km2 (Rajapakse 2003). Sambar appear to compose the largest proportion of leopard diet here with >75% of scat containing sambar remains (n > 30; Ranawana et al. 1998, Rajapakse 2003). To ensure a closed population, this capture-recapture study was conducted across 3 months from mid-February to mid-April 2012 (Karanth and Nichols 1998). This intermonsoonal period is typically dry and settled in the Central Highlands (De Silva 1997), and thus appropriate
Figure 1: (Left side) The location in Sri Lanka of Horton Plains National Park (HPNP) with reference to the area of occupancy and extent of occurrence of leopards (Kittle and Watson 2008). (Right side) The remote camera array within HPNP with park boundary, park office and prey transect locations also shown. Dark green denotes forest, and light green, grasslands. Note that prey transect locations were predominantly in grassland areas. Remote camera locations are indicated by the zone letter (A, B or C) and the camera number (1–7).
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A.M. Kittle and A.C. Watson: Sri Lankan leopard density in Horton Plains 3
for this kind of survey. Several pre-survey visits were made to HPNP to determine potential camera locations and monitor visitor flow and trail use. Due to heavy visitor use of HPNP roads and walking trails, the survey necessarily balanced effective study area coverage with practical aspects such as ensuring films were not filled with visitor images or cameras lost to theft. We therefore divided the study area into three zones, each encompassing seven remote camera locations, for a total of 21 study area camera traps (Figure 1). Each zone was active for six nights before cameras were moved to the next zone. This process was repeated until each zone had been covered three times. Thus the total trapping effort was [(3 zones × 7 locations) × 6 nights] × 3 sessions (or “occasions”) = 478 trap nights (Efford et al. 2009). Camera trap locations were divided into high and low tourist use areas (Table 1) with high use area cameras (n = 8) removed every morning and re-set every evening to avoid films being filled with images of visitors and/or their vehicles. Low use area cameras (n = 13) were always active and regularly checked for disturbance, dead batteries and finished film rolls. As a result there was varying effort at the camera locations
Table 1: Coordinates (UTM – Kandawala Grid), trail type, habitat description and human usage level for the 21 remote camera locations utilized during survey in Horton Plains National Park (February to April 2012). Detector A1 A2 A3 A4 A5 A6 A7 B1 B2 B3 B4 B5 B6 B7 C1 C2 C3 C4 C5 C6 C7
X 479742 479910 480247 478302 481656 479020 480663 477749 475936 474913 477356 478868 476690 478504 476187 476846 477680 478673 479848 478398 478496
Y Trail type Habitat 751903 752395 752944 751703 751580 751765 750902 751418 751767 751751 749798 752182 750539 750874 754252 753832 753107 755058 755317 753050 754448
Walking Walking Walking Walking Walking Paved Paved Walking Walking Walking Walking Animal Walking Walking Jeep Jeep Jeep Paved Walking Paved Paved
Grassland Grassland Grassland Grassland Forest Grassland Grassland Grassland Grassland Forest/grassland Forest Grassland Grassland Forest Forest Forest/grassland Forest Forest Forest Forest Grassland
Usage Low Low Low Low Low High High Low Low Low High Low High High Low Low Low High Low High High
Detectors are defined by zone (ABC) and camera number (1–7). Locations of low human usage had cameras set for 24 h, those of high usage had camera set for 13 h (18:00–7:00).
with low use area cameras recording images for 24 h and high use area cameras for 13 h (18:00–7:00). Camera traps consisted of two cameras, one on each side of the trail to ensure both flanks of photo-captured animals were documented. Leopard home range size in HPNP is unknown and adult female core areas in Sri Lanka’s prey-rich Yala National Park are
