17.1 Introduction

Srivilliputhur grizzled giant squirrel sanctuary is home to the threatened, Ratufa macroura. This sanctuary is situated at the eastern slopes of the Western Ghats of south India between 9°21′ to 9°48’N and 77°21′ to 77°46′E which were declared as a sanctuary in December 1989 (Tamil Nadu Forest Department 2007). The home range of R. macroura is restricted to riverine forests occurring at an elevation below 800 m MSL. Alagar kovil valley area of this sanctuary enjoys more than 50% of their population. The present study mainly concerns about the interaction of the grizzled giant squirrel with the available forest types that prevail in their home range. The report presents the data about the ecological interaction of the squirrel like feeding and nesting site selection in this sanctuary. Despite the fact that very little is known about its population status, density, distribution and ecology, only a few studies have been carried out on this species in India (Davidar 1989; Ramachandran 1992, 1993; Borges 1992; Joshua 1992; Sharma 1992; Joshua and Johnsingh 1994; Paulraj et al. 1992; Senthilkumar et al. 2007; Baskaran et al. 2011).

17.1.1 Ratufa macroura

This species is endemic to southern India (Kerala and Tamil Nadu) and Sri Lanka (Molur et al. 2005; Herlekar 2010) and classified under the order Rodentia of family Sciuridae. The common name grizzled giant squirrel came from the grey to brown colouration highlighted with white at the top of the tail, giving it a grizzled appearance (Prater 1971). This greyish-brown squirrel weighs around 2 kg and in the size of a small cat. It measures about 735 mm from the snout to the tail with just the tail being 360–400 mm long, longer than the body length. They are most active in the morning and early evening. Midday is a time of rest, and these squirrels are often observed sleeping on a branch (Prater 1971). The giant squirrel differs from other tree squirrels in that they do not sit upright when feeding. Instead, they balance on their hind feet with their body on one side of the branch and the tail acting as a counterbalance on the other side of the branch. Both their hands and feet are equipped with large powerful claws, making them agile climbers (Nowak 1991). These squirrels have a very distinct voice and can be very vocal. Like many primates, R. macroura react to the sighting of predators by provoking a general alarm, a series of calls and barks that alert the other community members to the nearness of the predator. Each individual has a home range that extends between 0.197 and 0.611 ha. (Joshua 1992). Males have range overlap with one or more females especially during the breeding season. There is very little data available on their reproductive cycle. It has a generation time of 7–8 years. The gestation period is believed to last about 28 days. During the breeding season, they construct drays at forked branches where the crowns of neighbouring trees meet. A large nest, similar in appearance to an eagle’s nest, is constructed. Parturition occurs within the nest, and the young remain there for about 2–3 months. Each litter consists of one or two young, and the female nurses them with her three pairs of mammary glands. It has been speculated that R. macroura may raise several litters each year (Kanoje 2008). R. macroura show limited social behaviour. They are mostly solitary, sometimes live in pairs and show high territoriality. They have been observed to camouflage with the tree branches by flattening themselves against the branches and remaining motionless when frightened. Overall, Ratufa macroura are very wary and keep them well hidden in the dense vegetation. R. macroura enjoy a diverse kind of diet that includes fruits, tender leaves, seeds, insects, bird eggs and even the bark of some trees. Plate 17.1 describes the digital documentation of feeding, resting and nesting behaviour of R. macroura from Srivilliputhur grizzled giant squirrel sanctuary.

Plate 17.1
figure 1

Different activities of grizzled giant squirrel

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17.1.2 Present Status of R. macroura

According to IUCN (2010), India has only an estimated population of less than 500 mature R. macroura. Habitat loss and degradation due to agro-industry farming, small-scale logging, selective logging, increase in human settlements, forest fire, interspecific competition, competition from alien species, hunting for local consumption purposes and presence of domestic predators have been observed to be the major threats for this species (Joshua and Johnsingh 1992, 1994; Molur et al. 2005; Joshua et al. 2008; Vanitharani et al. 2011). According to the IUCN red list of threatened species (Version 2014.2), the grizzled giant squirrel is facing a high risk of extinction in the wild. Information on the exact population size and density of grizzled giant squirrels in India is lacking.

17.1.3 Habitat the Determinant of Species Survival

Spatial and temporal changes of a forest are an important factor that determines the availability of the habitat for any species (Wilcox and Murphy 1984; McGarigal and McComb 1995). Many aspects of the behavioural ecology of animals in nature like dispersal, home range sizes, territoriality, dietary patterns and time-activity budgets are fundamentally linked to the amount of space used in a habitat and movements within it (Koprowski 2005; Verbeylen et al. 2009). The extensive canopy connectivity facilitates the movement and dispersal of arboreal mammals (Datta and Goyal 2008; Nandini and Parthasarathy 2008).

Grizzled giant squirrel being an arboreal mammal depends on forests and also possesses many other co-evolutionary relationships with the forest plants for the survival. The habitat of R. macroura requires the specific tree composition for their survival. They are critically dependent on mature forests that provide tree tissues and seeds as food, stems and canopies as launch sites and cavities and canopies as nest sites. Arboreal mammals are dependent on the spatial structure of the forest for nesting (Umapathy and Kumar 2000). These squirrels are known to prefer areas with good food availability and canopy connectivity to live and build their nests (Ransome and Sullivan 1997; Kumar et al. 2002; Kumara and Singh 2006; Srinivas et al. 2008). Individuals will have a better chance to thrive when they were more successful at finding food, mating and avoiding predators. Presence of nests in an area reflects the quality of the habitat around it and also indicates the degree of usage of the area by the species (Getty 1981; Datta and Pal 1993). Choosing a nest site is among the important choices made by an animal as it protects it from predation, provides thermoregulation and is also important in the breeding ecology of the animal. The giant squirrel constructs globular nests or drays using leaves and twigs, multiple in numbers within their home range (Srinivas et al. 2008).

Squirrels usually prefer trees significantly larger in all characteristics with large girth at breast height (gbh) and taller height with number of branches for nest building. The nesting trees were significantly larger in all characteristics than the non-nesting ones sampled in the population. According to Ramachandran (1992) such biased selection towards matured trees with greater canopy continuity could facilitate easy movement to and from the nest in all the directions, a major advantage to escape from predators and to move to other parts of the home range for foraging and other activities.

17.1.4 Threats for Survival

Fragmentation of the canopy and associated disturbances can bring about changes in the behaviour of arboreal mammals (Umapathy and Kumar 2000) with consequences for their survival and reproduction. Owing to the increasing human pressure, the habitats of grizzled giant squirrel are threatened by fragmentation through deforestation (Tikader 1983; Joshua 1992; Joshua and Johnsing 1994; Verbeylen et al. 2009).

The study has come out with few suggestions by saying that by increasing the Giant squirrel interactive tree species canopy in the affected/fragmented forest cover of the sanctuary will conserve the endangered squirrel as well as other dependent biodiversity of sanctuary.

17.2 Methods

Field survey was carried out to determine the plant-squirrel interaction in the Srivilliputhur grizzled giant squirrel sanctuary using the line transect method (Cox 1990). Each transect had a length of 2.0 km within the quadrates (5 km2). Grizzled giant squirrel interactive tree species vegetation sampling was done by using quadrate method in all the forest habitats of grizzled giant squirrel. In this study, mostly the riparian areas of the sanctuary are considered potentially suitable for the conservation of the grizzled giant squirrel, and hence the surrounding matrix habitat was ignored. The grizzled giant squirrel interacting tree species are identified as ‘focal plant’ species. A small sample of plant twig from the focal plant species was collected, and a herbarium is maintained in the Zoology Department Research Centre of Sarah Tucker College. The vernacular names of the tree species were recorded, and their scientific names were ascertained by Dr. Chelladurai, (Retd.) Botanist, Government Siddha Medical College, Palayamkottai, and Dr. Gopalan, (Retd.) Scientist, Botanical Survey of India, Coimbatore. Grizzled giant squirrel’s interaction with the focal tree species were directly observed during the active forage time and during breeding seasons. The observations were recorded from a spot about 10.0–20.0 m away from the focal plant using a pair of binoculars. Extended watches (a minimum of 1.0 h) were done near the focal plant. During the extended watch, feeding and nest building activities with the focal plants were documented.

17.3 Result and Discussion

Being an arboreal, diurnal giant squirrel inhabits tall larger trees of the sanctuary for food, shelter and movement. Understanding the species distribution and its resource requirements is essential for its long-term conservation plans. R. macroura interact predominantly with 35 tree species that prevail in the sanctuary, mainly for their survival. 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 (Ramachandran 1992; Paulraj and Kasinathan 1993; Paulraj et al. 1992; Molur et al. 2005; Vanitharani et al. 2011). Nesting and foraging interactive focal trees species of the grizzled giant squirrel at Srivilliputhur Wildlife Sanctuary were documented in Table 17.1.

Table 17.1 Nesting and foraging trees of grizzled giant squirrel Ratufa macroura in Srivilliputhur Wildlife Sanctuary
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17.3.1 Foraging Interactions

The grizzled giant squirrel (Ratufa macroura) plays an important role as a seed disperser to their foraging trees via dropping seeds as they cruise over the canopy; the key tree species dependent are Artocarpus heterophyllus, Artocarpus hirsuta, Ficus benghalensis, Ficus religiosa, Ficus racemosa, Tamarindus indica, Mangifera indica, Lannea coromandelica, Morinda tinctoria, Syzygium cumini, Eriodendrum pentandrum, Polyalthia suberosa, Aglaia elaeagnoidea, Chassalia curviflora and Sapindus emarginatus distributed in the dry deciduous forests of Srivilliputhur Wildlife Sanctuary. During the extended watch near some of these key tree species, the squirrels were observed to eat tender leaves of Tamarindus indica. Joshua (1992) and Ellerman (1961) also reported similar feeding habits of the squirrel. Ripe fruit pulp of M. indica and Artocarpus spp., fig fruits and teak flowers are also the most significant contributor of the diet of these squirrels. Overall, the present study has recorded that the squirrel feeds on a total of 35 tree species. Among their interacting trees, 37% (15 species) are used for both nesting and foraging trees. During the non-fruiting season or during the scarcity of the fruits, grizzled giant squirrel devours the bark and leaves of some key tree species. Becker et al. (1985) and Borges (1992, 2007) suggest these squirrels prefer fruits and seeds, when they are available. Squirrels usually avoid consuming fresh seeds of S. cuminii since fresh tissues (bark, fruit pulp, seeds) of these trees are known to be hypoglycaemic (Rafiullah et al. 2006; Villasenor and Lamadrid 2006).

17.3.2 Nest Selection Interaction

Grizzled giant squirrel being a canopy dweller largely depends on the tree canopy contiguity for their movement, nesting and breeding (Joshua 1992; Thorington and Cifelli 1989). Giant squirrels are known to build nests in several trees, sometimes even within a small area (Prater 1971). Of the 35 squirrel interacting key tree species within the sanctuary, the squirrels preferred only 25 of them for nest building. It is noteworthy that the tree species Pterocarpus marsupium, Stereospermum chelonoides, Schleichera oleosa, Tamarindus indica, T. arjuna and Maesa indica are seen with multiple nests. S. oleosa was the most preferred tree species for nesting followed by M. indica. These trees are mostly distributed along the rivers and streams. The dense canopy cover and higher canopy height of these trees provide contiguity that could offer better protection and way to escape from the predators. Nagarajan et al. (2011) suggested that many arboreal dwellers prefer this type of habitat.

According to Kanoje (2008) in the Sitanadi Wildlife Sanctuary, the giant squirrel’s most common nesting trees were Terminalia tomentosa and S. oleosa. The other major species of nesting trees were S. cuminii, T. indica and Terminalia spp. Kanoje also recorded 207 nesting trees and observed approximately 77.68% of the nests were found on deciduous trees (25 species), while only 5 species of nesting trees were located in the evergreen forest.

17.3.3 Threats for Survival

Human interference through various means within the sanctuary threatens the well-being of the habitat used by the giant squirrels. Threats arise as poaching, loss of habitat due to illegal cutting of trees, overgrazing by livestock, frequent forest fires in the summer season and overexploitation of non-timber forest produce (Joshua and Johnsingh 1994). Forest fragmentation is considered to be the biggest threat to global biodiversity (Wilcox and Murphy 1984). The ability of a species to persist at sites after disturbance depends on its ability to modify its behaviour, foraging and dietary patterns to withstand the changes in forest structure and composition. The observations suggest the grizzled giant squirrel really find it hard to cope with the changing habitat. Keeping this in mind, the present study has suggested the plantation of the 35 grizzled giant squirrel interacting tree species in the fragmented forest area to conserve the grizzled giant squirrel.

17.3.4 Management Recommendations

Grizzled giant squirrel shows restricted distribution mostly in riverine habitats. But the riverine habitats along the sanctuary are generally patchy in forest coverage. Restoration of the habitat in the gap and maintenance of canopy continuity through afforestation by the preferred tree species like T. indica, S. oleosa and M. indica can enhance the population size of the grizzled giant squirrel as well as the other faunal diversity.

In addition reducing commercial exploitation of T. indica fruits in large scale by the local people and government sectors can lessen the anthropogenic pressure. Strict legislation and management actions against grazing pressure along the riverine habitats will also help to achieve neutral restoration of the forest cover in the sanctuary and will also enhance the long-term survival of grizzled giant squirrel species. Still these threatened species lacks an updated comprehensive database about the distribution and population status across its habitat. Being a threatened species, it definitely deserves the attention of conservationists. Paulraj (1991) suggested that unless the species receives immediate attention for its protection and conservation, it will be a difficult task to save it from extinction.

17.4 Conclusion

Accurately forecasted impacts of disturbance on the native flora and fauna indicates, it is essential to conserve the forest habitats of the sanctuary to conserve biodiversity and the threatened Ratufa macroura, grizzled giant squirrel. The present study has identified 35 native and giant squirrel interactive tree species. At the same time, this interaction also reviews the complement and reward gained by the squirrels from the plants for their rendered propagation services. If these squirrels preferred key tree species are planted in the fragmented and degraded forest areas that will enhance natural forest restoration and also habitat for the native threatened and endangered animals.