The squirrels are included under family Sciuridae and order Rodentia whose descendants are known to be living since last 30 to 40 million years ago. Members of Sciuridae family comprises of a variety of diverse species such as the terrestrial chipmunks, marmots, semi-fossorial Praire dogs and arboreal tree and flying squirrels. The Sciurids are capable of occupying different niches from temperate to tropical regions of the world. They are diurnal and chiefly herbivorous feeding on plants, seeds, fruits, leaves and occasionally on small vertebrates and insects (Thorington et al 2012).
Earlier, squirrels were classified in two subfamilies: Sciurinae and Pteromyinae that included tree, arboreal and flying squirrels respectively. However with recent findings based on molecular evidences, squirrels are classified in 5 sub-families: Ratufinae,Sciurillinae, Sciurinae,Xerinae, andCallosciurinae(Stephan and Shawn 2006). Large-bodied squirrels belong to the Ratufinae family. Among the terrestrial squirrels, the largest ones are marmots of North America and Asia while the largest arboreal squirrels are the giant squirrels from South and South-East Asian countries.
Although arboreal squirrels are known to damage fruits in orchards, feed on crops (Thorington et al 2012), and cause injuries to trees by debarking, they also provide certain valuable ecosystem services and therefore have an important role in biodiversity conservation. Ecological studies on Indian giant squirrel Ratufa indica have pointed out the importance of canopy connectivity, tall trees, contiguous forest patches and presence of lianas for supporting viable population of the species (Ramachandran 1988, Borges 1989, Ramakrishnan 1990, Datta and Goyal 1996, Srinivas 2008, Kankoje 2006). Apart from being an indicator species for structurally diverse forests, arboreal squirrels play an important role in seed-dispersal. Seeds form a majority portion of their food item (Ramachandran 1989, Borges 1992), bark, pith, flowers, fruit pulp and figs were consumed as per the availability (Borges 1993).
Although scatter-hoarding and larder–hoarding is best known most among temperate squirrels, it has been observed recently in arboreal Malabar giant squirrel (Somanathan et al 2007). Squirrels are known to assist in germination of a few hardwood species by terrestrial seed hoarding and also provide food resources to avian furgivores in the vicinity. Fungi also forms a part of the squirrels diet and thus assists in dispersal of fungi in the forests.
Members of Genus Ratufa
Giant squirrels belong to Genus Ratufa that consists of 4 species of canopy-dwelling squirrels generally restricted to sub- canopy with diet comprising mainly of fruits, seeds, bark and leaves of tropical trees (Borges 2007, Thorington et al 2012). All the four species of Ratufa are on Appendix II of CITES and Schedule I of Indian Wildlife (Protection) Act 1972.
Ratufa affinis is a brown giant squirrel inhabiting rainforests of south-east Asia. Nine sub-species have been identified. The species is included under near-threatened category of IUCN.
Ratufa bicolor is a black and white giant squirrel of North–east India and South-East Asia with eleven sub-species. It occupies broad-leaf evergreen forests and is listed as near-threatened by IUCN.
Ratufa indica is a maroon and buff colored giant squirrel endemic to India with four sub-species. Widely distributed from semi-evergreen, moist deciduous to riparian forests in drier areas, this species is now under the least concern category of IUCN.
Ratufa macroura has ablack brown and buff coat, prefers evergreen forests. It has three sub-species, of which one is confined to southern India and other two are in Sri Lanka. The species is near-threatened as per the IUCN status.
1.5 The Indian Giant Squirrel R. indica
Of the four species described above, R. indica has been studied extensively in the country. The species is widely distributed in Indian peninsula (Abdual Ali and Daniel 1952) and is almost totally arboreal and very rarely come down on the ground (Ramachandran 1988, Borges 1989). Their feeding activity is mainly in top to mid-canopy (Ramakrishnan 1990, Borges 1989, Kumara and Singh 2006); they prefer higher GBH (> 150 cm) and taller trees (> 15 m) for feeding and nesting (Datta and Goal 1996, Baskaran et al 2011). Leafy trees with canopy continuity and liana growth are preferred for nesting (Ramachandran 1988, Datta and Goyal 1996, Umapathy and Kumar 2000, Kankoje 2008, Baskaran et al 2011) and many times large nesting trees also served as feeding trees (Kankoje 2008, Baskaran et al 2011).
Giant squirrels are found across a range of natural forests from moist deciduous to dry deciduous forests types, riparian forests (Borges 1989, 1992, Datta and Goyal 1996, Srinivas et al. 2008, Kankoje 2008, Jathana et al 2008, Baskaran et al 2011), old mature teak forests (Ramachandran 1988) and teak-mixed forests (Kumara and Singh 2006) R.indica has five recognized sub-species based on their pelage color (Moore and Tate 1965).
The palest and albinistic form R. i. dealbata (Blanford, 1897) from Gujarat Western Ghats
R. i. bengalensis (Blanford, 1897) from wet crestline forests in Brahmagiri in Karnataka Western Ghats and to its eastern sides
R. i. centralis (Ryley 1913) from drier teak associated forests of Central India
R. i. maxima (Schreber 1784) from Malabar region in Kerala and
R .i. indica from the Sahyadri-Konkan region of Maharashtra, Goa and northern parts of Karnataka Western Ghats (Prater 1980).
Studies on R. indica have been carried out in the Protected Areas in Western Ghats and Central India. Even within the Western Ghats, the southern Western Ghats have been extensively studied for its ecology and distribution status.
Prachi Mehta Ecological Studies on R. indica
An ecological study on R .i .maxima in Parambikulum Wildlife Sanctuary (WLS) in Kerala Western Ghats in south India was carried out from 1983 to 1985 by Ramachandran (1988). The study focused on the home-range, diet and breeding behavior of giant squirrels in the area. The study reported that giant squirrels require tall trees with interlinking crowns for nesting and feeding. Primarily, they feed on seeds but during the non-availability of seeds they also feed on leaves barks and twigs. The study reported a density of 31 individuals for 100 km2in the area
Renee Borges studied the resource use and foraging ecology of R. indica in Bhimashankar WLS in Maharashtra Western Ghats during 1983 to1988 (Borges 1989a, b). The study revealed that 95% of the daily giant squirrel diet was contributed by lianas and stressed the importance of liana conservation. The home range of squirrel was reported to be around 0.8 to 1.0 ha in the study area. The density of squirrel in Bhimashankar Rai (riparian area within Bhimashankar) was reported to be 100 individuals / km2 (Borges 1989 Unpublished Report to USFWS)
Borges (1990, 1992) studied the nutritional analysis and foraging strategies of giant squirrels. The study revealed that squirrels have adapted to a generalist feeding strategy owing to its large body size and constraints in availability of highly nutritious food items throughout the year (Borges 1992). Figs as fruits are taken by those individuals who have them in their territory as squirrels are sedentary and have small home ranges (Borges 1993).
During 1992, Datta and Goyal (1996) carried out a short-term study on R .i .centralis comparing habitat use in a riparian forests and dry deciduous forests in Bori Wildlife Sanctuary in Central India. The study reported preference of squirrels on tall (> 15 m) and higher GBH (> 150 cm) trees for feeding and nesting.
Baskaran et al (2011) carried out ecological study of R. indica in Mudumalai Wildlife Sanctuary in Tamil Nadu. The squirrel diet showed high percentage of teak seed, bark, leaf and flowers in their diet. Tall trees with interlinking canopy were preferred for nesting.
Kankoje (2006) studied nest site selection by R. i. centralis in Sitanadi WLS in Central India. The study revealed squirrel’s dependence on tall trees with interlinking crowns as nest trees.
Somanathan et al. (2007) reported an interesting record of seed storage in the nests of R. indica in Bhimashankar. While arboreal larders are useful in supplementing diet to individuals facing food storage in lean fruiting season and is common in temperate regions, it has not been observed in tropical forest so far. Also, terrestrial seed hoarding assists in plant germination, while arboreal hoarding of seeds had no clear role for plant germination therefore making this observation more intriguing.
Studies on Distribution Status of R. indica
A status survey of R. indica by Mali et al. (1998) was carried out from 1992 to 1993 in Western Ghats and Central India in Protected Areas and intervening Reserved Forests. The survey confirmed local extinction of R. i. dealbata from Gujarat and vulnerable status of R. indica from Maharashtra Western Ghats. The study also compared the home range and density of R .indica in Bhimashankar WLS that was studied earlier by Borges (1989). After a gap of 10 years, the home range had doubled and a decline of 30 % in the population was recorded from the intensive study area. The cause of this decline was mainly habitat degradation in Bhimashankar WLS.
From 1994 to 1996, Umapathy and Kumar (2000) examined the occurrence of arboreal mammals including giant squirrels in rain forest fragments in Indira Gandhi WLS in southern Western Ghats. The authors reported an increase in density of giant squirrels from disturbed and smaller fragments of forests. The explanation for this was that since giant squirrel has smaller home range it could occupy in smaller fragments and in absence of other arboreal mammals from smaller fragments, the squirrels had less resource competition and could survive in moderately disturbed areas.
Madhusudan and Karanth (2000) compared densities of nine mammals including R. indica from Alkeri and Nalkeri sites of Nagarhole National Park in South India. Although both the sites were within the PA and had similar size and forest types, Alkeri had significantly lower density of R. indica (5.5. km2) than Nalkeri (8.5 /km2). Intensive hunting at Alkeri was the main reason for the difference in the R. indica density between the sites.
Between 1998 to 2000, Baskaran et al (2011) estimated the population of giant squirrels from Mudumalai WLS in Tamil Nadu. A density of 2.9 individuals /km2 was reported from the study area with an estimated mean home range to be 1.3ha.
From 2001 to 2004, Kumara and Singh (2006) assessed the status of R.indica in 3 Protected Areas of Western Ghats of Karnataka namely. Pushpagiri, Brahmhagiri, Nagarhole, and forests of Sirsi–Honavar. The squirrel encounter rate was higher in Nagarhole National Park and in moist forests of Srinegri Forests. Giant squirrels were detected only from the narrow crest-line forests of Western Ghats but were found to be absent from plains of costal Karnataka and eastern Karnataka.
Between 2002 to 2003, Jathana et al. (2008) used line transect sampling method to estimate population density of R. indica in 3 Protected Areas of Bhadra Tiger Reserve, Nagarhole Tiger Reserve and Bandipur Tiger Reserve in Karnataka. The encounter rates and densities were highest in moist forests. The encounter rates ranged from 0.18 to 0.79 in dry to wet evergreen forests respectively.
From 2004 to 2008, Molur and Singh (2009) carried out a survey of non-volant mammals in Kodagu District in Karnataka and recorded the presence of giant squirrels in large undistributed fragments of Western Ghats.
Molur et al (2005) carried out a detailed assessment of non-volant mammals in India. The giant squirrel was placed in the category on Vulnerable in 2003 because of habitat degradation due to increase in agro-industry, large scale monoculture plantations, timber harvesting and hunting for meat.
In 2005, Srinivas et al. (2008) carried out an occupancy assessment of giant squirrels in Kalakad Mundantharai Tiger Reserve (KMTR) in Tamil Nadu in South India. The occupancy rates of squirrels were higher in contiguous patches of evergreen and moist forests and lowest in drier, degraded and disturbed forests.