Some aspects of the ecology of the Indian Giant Squirrel Ratufa indica (Erxleben, 1777) in the tropical forests of Mudumalai Wildlife Sanctuary, southern India and their conservation implications
Nagarajan Baskaran 1, S. Venkatesan 2, J. Mani 3, Sanjay K. Srivastava 4 & Ajay A. Desai 5
Bombay Natural History Society, Bear Bungalow, Kargudi, The Nilgiris, Tamil Nadu 643211, India Present Address: Asian Nature Conservation Foundation, Innovation Centre, Indian Institute of Science, Bengaluru, Karnataka 560012, India 4 Tamil Nadu Forest Department, Panagal Building, No. 1 Geenis Road, Saidapet, Chennai, Tamil Nadu 600015, India 5 Present Address: BC 84 Camp, Belgaum, Karnataka 590001, India Email: 1 baskar@ces.iisc.ernet.in (corresponding author), 4 sks2700@yahoo.co.in, 5 ajayadesai.1@gmail.com
1,2,3,5 1
Abstract: The Indian Giant Squirrel Ratufa indica, an endemic species to India, is widely distributed from the evergreen to moist and dry deciduous forests of Western and Eastern Ghats and the central Indian hills. We studied its population distribution, activity, feeding, ranging and nesting behaviour across three major habitats in the tropical forests of Mudumalai Wildlife Sanctuary, southern India, during 1998–2000 to manage the species effectively. Extensive survey of the three major habitats—tropical moist, dry deciduous and dry thorn—in the sanctuary shows that its distribution is continuous in moist and dry deciduous forests with good canopy contiguity and patchy along riverine areas in dry thorn and dry deciduous forests with sparse trees and broken canopy. Density estimates using 55 direct sightings from 199 km line transects show a mean of 2.9 (± 0.313) squirrels/km2. Daylight activity and feeding patterns assessed through 24,098 minutes of focal sampling reveal that animals feed and rest equal amounts of time. The diet constitutes seeds, bark, petioles, leaves and fruits from 25 plants, with Tectona grandis as the principal food source (41%). Its home range size varied from 0.8–1.7 ha with a mean of 1.3ha. Nesting characteristics assessed through 83 nests surveyed along 54km transects showed that the squirrel uses 15 of the 33 tree species found, with higher preference to Schleichera oleosa and Mangifera indica. Nest trees are significantly larger in height, gbh and canopy contiguity than nearest non-nest trees, which are attributed to better protection and escape from predators. Maintenance of diverse natural habitats and reduction in anthropogenic pressure are measures suggested for the conservation of giant squirrel populations in the study area. Keywords: Breeding, diet, ecology, feeding, population, ranging, Ratufa indica.
INTRODUCTION The Indian Giant Squirrel Ratufa indica is a large arboreal squirrel endemic to India (Image 1). The species is widely distributed in peninsular India (Abdulali & Daniel 1952; Corbet & Hill 1992) from the evergreen to moist and dry deciduous forests of Western (Ramachandran 1988, 1992; Rout & Swain 2005), and Eastern Ghats (Kumara & Singh 2006) and central Indian Hills (Agarwal & Chakraborty 1979). The species is listed as Least Concern in Red List of IUCN (Rajamani et al. 2009) and of Schedule I (Part I) of the Indian Wildlife Act (1972). The species, like many other squirrels of its genus, is a top canopy dweller, which occasionally comes to the ground (Ramachandran 1988), mostly to overcome breaks in canopy continuity. The species mostly feeds on seeds, leaves, flowers and bark from trees. It is a solitary living species, constructs globular nests or dreys with leaves and twigs (Borges 1989; Thorington & Cifelli 1989; Ramachandran 1992). Considering its arboreal nature and dependence on
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Journal of Threatened Taxa | www.threatenedtaxa.org | July 2011 | 3(7): 1899–1908
trees for food, shelter and movement, it is apparent that the composition of tree species and structural attributes of the forests play a major role in the use of the habitat by the giant squirrel (Borges 1989; Ramachandran 1992; Datta & Goyal 1996). Understanding the species distribution and its resource requirements are essential for its long-term conservation plans. Ratufa indica centralis is very common in parts of Nilgiri Biosphere Reserve; yet no published ecological data essential for the management of the species is available from this region. This paper addresses the basic ecological aspects such as population, factors influencing its distribution, foraging, nesting and ranging behaviour of the Indian Giant Squirrel in the tropical forests of Mudumalai Wildlife Sanctuary, which is part of the Nilgiri Biosphere Reserve.
METHODS Study area: The study was carried out in Mudumalai Wildlife Sanctuary (presently a Tiger Reserve) during 1998–2000. The sanctuary lies between 11032’–11045’N and 76020’–76045’E, and is a part of the Nilgiri Biosphere Reserve. It is bounded on the north by Bandipur Tiger Reserve, to the west by Wayanad Wildlife Sanctuary and to the south and east by Nilgiri North Forest Division. The terrain is undulating with an average elevation of 900–1000 m. Only the Moyar River and a few bigger streams that drain into it are perennial. Additionally, several large manmade water holes act as water sources during the dry season for wild animals. The study area has two
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wet seasons (the southwest monsoon: May–August and northeast monsoon: September–December) and a dry season (January–April). The rainfall has a marked east-west gradient with eastern areas receiving 600– 800 mm of precipitation annually and the western regions 1800–2000 mm. Temperature ranges from 80C in December to 350C in April (Baskaran 1998). The vegetation follows a gradient similar to the rainfall, with dry thorn forests dominating the eastern side of the sanctuary followed by dry deciduous short grass and dry deciduous tall grass forests in the middle, and moist deciduous forests to the western side. There are also a few patches of semievergreen forest along the western side of the sanctuary. We selected four sites for detailed behavioural data collection on giant squirrels in four different habitats, which include moist deciduous forest, a dry stream in the dry deciduous forest, a riverine habitat and a teak plantation. Distribution pattern: We mapped the distribution of giant squirrel based on the presence and absence of squirrel direct sightings and their nests walking along 65 transects laid across the sanctuary covering all major and microhabitats used for density estimation of squirrel and their nests. In all the major habitats, an effort was made to sample the riverine (along river and stream) microhabitats as they are distinct from surrounding areas in terms of tree species composition and canopy contiguity, especially in the dry deciduous and dry thorn forest. Population density: We used the line transect method (Burnham et al. 1980) to estimate population density. In total, 65 transects with length varying from 2–4 km, laid systematically covering all the habitats and microhabitats across the sanctuary were sampled once partly (16 transects) during May 1998 and rest in May 1999. The transects were walked during morning (0600–1000 hr) or evening (1600–1800 hr) and at every sighting of squirrel we recorded the perpendicular distance, using range finders and group size of the squirrel. In total, 55 sightings were recorded from 199.3km line transect walk. Mean group (cluster) size (G) and its standard error (SE) was estimated based on data where complete counts of individuals were obtained on transects. Population density was estimated using distance-sampling techniques following the software DISTANCE version 6.0 (Buckland et al. 2004; Thomas et al. 2005). Grouping the data into 10-m perpendicular intervals,
Journal of Threatened Taxa | www.threatenedtaxa.org | July 2011 | 3(7): 1899–1908
Ecology of the Indian Giant Squirrel
N. Baskaran et al.
squirrel cluster density (C) and its SE was estimated evaluating different models of detection probability, viz. uniform, half-normal and hazard-rate with three series adjustment terms and used the minimum Akaike Information Criteria (AIC) as the standard model selection procedure to select the best model for estimating density. Individual squirrel density (D) was arrived at multiplying the mean group size (G) by the squirrel cluster density (C). Standard error of individual squirrel density (seD) was calculated using standard error of cluster density (seC) and standard error of mean group size (seG) using Goodman’s (1960) formula: (seD) = C (seG) + G (seC) – (seC) (seG) and used the same to work out the 95% confidence limit of individual squirrel density. Activity pattern and feeding: Data on activity and feeding were recorded through direct observation using the focal animal sampling method (Altmann 1974). Observations were made for a period of two days (six hours per day: either 0600–1200 hr or 1200–1800 hr) per month from each site. Daylight hours from 0600 to 1800 hr were divided into 12 one-hour blocks for sampling and an attempt was made to sample each one-hour block at least once a month. Focal sampling was made at 15min interval (of 10min observations and 5min break). Thus, observations started at nearest 1st or 15th or 30th or 45th minute of any hour of sighting time. At every focal sampling, the subject was continuously observed for a period of one minute and recorded its activity (feeding, resting, moving and others: inter and intraspecific activities, drinking/ water licking (from tree holes and leaf surfaces), urination, defecation and nest construction) at every minute interval for a period of 10 minute; in case of feeding, plant species and parts consumed. While on feeding, the squirrel often goes to the tip of branches and collects (cuts) the food items (fruits, seeds, leaves etc) with its mouth and moves to the thick horizontal branches by holding the food items mostly in the mouth and some time in the forelimb, where branch is stronger and it is convenient for the squirrel to sit and feed. In the present study, such movements over small distances within the same tree while on feeding (with the food materials in mouth or forelimb) were clubbed with feeding activity. Time spent on various activities and feeding of different plant species was computed season-wise for each habitat separately from the 12 month observations.
Nesting characteristics: Nest site characteristic features were collected along 25 transects covering three major habitats in the sanctuary. For each nest located along the transect, we have recorded variables such as tree species used for nesting, their height, girth at breast height (GBH), number of main branches, canopy heights, canopy contiguity on all four directions, height of nest from ground. Squirrels jump from one tree to another and gaps between trees of
