Journal of Threatened Taxa | www.threatenedtaxa.org | 26 April 2019 | 11(6): 13720–13726

Nesting trees of the Red Giant Gliding Squirrel Petaurista petaurista (Mammalia: Rodentia: Sciuridae) in a tropical forest of Namdapha National Park, India

Murali Chatakonda Krishna ¹, Awadhesh Kumar ²  & Om Prakash Tripathi ³

1 Amity Institute of Forestry & Wildlife, Amity University, Sector 125, Noida, Uttar Pradesh 201313, India.

1,2,3 Department of Forestry, North Eastern Regional Institute of Science and Technology (Deemed University), Nirjuli, Arunachal Pradesh 791109, India.

1 mkchatakonda@amity.edu (corresponding author), 2 tpileatus@gmail.com, 3 tripathiom7@gmail.com

Abstract: The present study investigated the nesting habits of the Red Giant Gliding Squirrel in the tropical forest of Namdapha National Park, India within the time period of 2012–2013.  Gliding squirrel nest trees were located by searching for them with using spotlighting during evenings and early mornings.  For each den site we recorded data on nesting tree species, total height of tree, height of the nest on tree, tree diameter at breast height (DBH), and canopy connectivity of the nesting tree.  We observed P. petaurista using cavity nests (n=27) in eight tree species.  The majority of nest trees observed were in Altingia excelsa (40.7%) and Terminalia myriocarpa (22.2%).  Trees with less canopy connectivity were preferred for nesting where 59.3% of nest trees had <25% canopy connectivity.  Petaurista petaurista nested in trees with an average of 31.1±0.86m (Mean ± SE) height and the nests were located at a mean height of 17.8±0.89m (SE) (min & max: 9.3m & 35.2m).  Mean DBH of nesting trees was 70.6±0.98cm (SE) (min & max: 38.2cm & 168.8cm).  This data helps in filling the gaps on the denning ecology of the species and may be useful for the management and conservation purpose of forest trees.

Keywords: Arboreal nests, Arunachal Pradesh, giant gliding squirrels, canopy connectivity, northeastern India, secondary cavity nesters.

Introduction

Understanding the ecology of a species is crucial for its conservation and management.  Although mammals are among the most studied taxon groups, the ecology of nocturnal arboreal mammalian ecology remains understudied (Bonnet et al. 2002; Clark & May 2002; Jayasekara et al. 2007).  Due to knowledge gaps, nocturnal arboreal mammals, such as gliding squirrels, are underrepresented in conservation action plans (see Koprowski & Nandini 2008; Datta & Nandini 2014).

Nesting ecology of gliding squirrels is an important aspect of their biology and is pertinent to their conservation and management.  Gliding squirrels use nests for diurnal refuge, shelter from predators and adverse weather conditions, reproduction, and hoarding sites (Cowan 1936; Weigl & Osgood 1974; Weigl 1978; Lee et al. 1986; Bendel & Gates 1987; Shafique et al. 2009).  Three types of nests are used by gliding squirrels — tree-cavities, external leaf nests and subterranean nests (Carey et al. 1997; Hackett & Pagel 2003; Holloway & Malcolm 2007).  The availability of large, dying, and dead trees has been found to influence nesting strategies among gliding squirrels (Carey et al. 1997; Menzel et al. 2004).  Subterranean nests are the least common ones that are observed under the tree roots, downed logs and under rocks (Gerrow 1996; Hackett & Pagels 2003; Diggins et al. 2015).  In areas with high snag densities, cavity nests tend to be most prevalent, and in low snag areas with timber harvesting and low cavity availability high external nest use is observed (Carey et al. 1997).  At times, drey’s are even observed where the squirrels build nests in the tree branches (Hanski et al. 2000).  Of the various nesting types discussed above, cavity-nesting has evolved as an adaptation to avoid predation (Martin 1998) and such nesting is considered important for gliding mammals like gliding squirrels (e.g., Taulman 1999; Holloway & Malcolm 2007) and gliding marsupials (e.g., Traill & Lill 1997; Lindenmayer 2002).

The objective of our study was to determine nesting tree characteristics of the Red Giant Gliding Squirrel in tropical forests of Namdapha National Park of Arunachal Pradesh, India (Image 1).

Material and methods

Study Site

The study was carried out at Namdapha National Park (NNP; 27.391–27.661 0N & 96.250–96.975 0E; area  1,985km²) which lies in the eastern Himalayan region of Arunachal Pradesh, India (Fig. 1). The park contains some of the northernmost tropical rainforests of the world (Proctor et al. 1998) and the temperature in the park varies along with altitude ranging between 4–35 0C at altitudes below 2,000m and at higher elevations, the temperature often drops below the freezing point in winters (Ray et al. 2015).  Monthly precipitation ranges from a minimum of 1,400mm and maximum of 2,500mm, 75% of which falls between April and October (Kumar et al. 2009).  Details on park vegetation are reported by Ghosh (1987), Nath et al. (2005), and Ray et al. (2015).  Our study was carried out in Deban (27.4830N; & 96.3830E), Gibbons Land (27.5000N & 96.3160E) and Hornbill Camp (27.5330N & 96.4330E) (Murali et al. 2014) areas within the park and the elevation range of these three study sites range between 200m and 550m.  The study sites are dominated by tall trees ranging from 15m to 45m including common species such as Duabanga grandiflora, Neolamarckia cadamba, Biscofia javanica, Cinnamomum sp., Shorea assamica, Castanopsis sp., Ficus sp., Syzygium fruticosum, Spondius axillaris and Toona ciliata.  Our study sites were approximately 5–10 km apart from each other.  All three sites were selected based on the frequent sighting of Red Giant Gliding Squirrels and site feasibility.

Investigation of nesting cavities

The data on the squirrel nests was collected from October 2012 to September 2013.  A minimum of 4–5 days were spent in the field per month during the study period to locate the nests.  The nests were located by searching for gliding squirrels with headlamps (Energizer HDL33A2E (Energizer, USA)), during the evenings (17.00h) and early mornings (04.00h) when gliding squirrels usually leave and return to their nests (Shafique et al. 2009).  Only those trails, however, were monitored which were marked for estimating encounter rates of the species.  Also, opportunistic sightings of the nests were also included in the data whenever a nest was sighted. Upon locating the nesting site, the following nesting characteristics were recorded: tree species, total height of the nesting tree (m), height of the nest on the tree (m), diameter at breast height (DBH) (cm) of the tree, and canopy connectivity of the nesting tree.  The height of the nest was measured using laser distance measurer (Bosch GLR225; accuracy ±1m (Robert Bosch GmbH, Germany).  We followed Herlekar (2010) to determine canopy connectivity of the nesting tree, where connectivity was calculated based on the canopy shared by neighbouring trees.  If the nesting tree was covered by canopy on four sides, we considered the canopy connectivity was 100%, whereas if nesting trees canopy had canopy connectivity on three, two, one, or no sides, connectivity was considered 75%, 50%, 25%, or 0%, respectively (Herlekar 2010).  Additionally, to compare selected trees to nearby trees, we measured DBH (cm), tree height, and distance from nesting tree (m) of the four nearest trees to each individual nest tree.  The nearest trees were identified based on the four imaginary quartiles which lie around the nesting tree.  All the distances and tree heights were measured using a Nikon Rangefinder (Nikon 6x21 Forestry Pro, Nikon Corporation, Tokyo, Japan).

 The lengths of census trails ranged between 0.5km and 2km.  All the trails surveyed were pre-existing and  no fresh trails were cut in order to minimise the disturbance in the area.  Data on vegetation was collected along these trails using point centred-quarter method (Cottam & Curtis 1956).  Absolute density and relative density of the trees were calculated following Mitchell (2010) where the absolute density of a species was estimated as the proportion of quarters where the species was found.

Results

We observed Red Giant Gliding Squirrels using a total of 27 nests during the study and also found that the Red Giant Gliding Squirrel used eight tree species for nesting (Image 2): Altingia excelsa (n = 11), Terminalia myriocarpa (n=6), Castanopsis indica (n = 3), Shorea assamica (n=2), Syzygium fruticosum (n=2), Cinnamomum bejolghota (n=1), Cinnamomum glaucescens (n=1), and Artocarpus chaplasha (n=1).  The nest trees exhibit low canopy connectivity, where most trees had <25% canopy connectivity (59.3% of nest trees), followed by 25.9% of nests with 50% canopy connectivity, and 14.8% of nests with connectivity >75%.  The mean measurements of the nesting tree species are presented in Table 1.

Of the neighbouring trees (n=108) observed adjacent to nesting trees, ~93% (100 trees belonged to 25 species) were living trees and 7% (8 trees) were dead snags.  And among the 25 species, nine species (n=61) were observed as feeding trees (Table 2).  Of the 27 identified nesting trees, 24 had canopy connectivity with feeding trees.  12.5% of nesting trees were surrounded by four feeding trees, 33.3% were connected with three feeding trees, 45.8% were connected with two feeding trees, and 8.3% were connected with a single feeding tree.

Discussion

Studying the life history traits and ecology of gliding squirrels is difficult due to their nocturnal habits and secretive nature.  Our study is the only document presenting the nesting preferences of the Red Giant Gliding Squirrel in India till date.  During the study period we observed Red Giant Gliding Squirrels nesting only in the cavities.  This may be due to availability of tree cavities for nesting at our study site.  Firstly, cavities may provide better protection than drey from predators, such as arboreal civets (Krishna et al. 2015).  Secondly, the study area receives heavy rainfall during monsoon and thus cavity nests may offer more protection from inclement weather than drey nests.  The Japanese Giant Gliding Squirrel Petaurista leucogenys drey’s are observed in areas where there was scarcity of tree hollows (Haneda 1955; Tachibana 1957).  Also, it was noted that the species preferred large trees with higher DBH for nesting.  Similar observations were reported earlier in many other studies (see table 3).  In general, gliding squirrels are reported to need tall mature forests for nesting as they are cavity nesters (Ransome et al. 1997) and are critically dependent on mature forests for food, and movement (Verbeylen  et al. 2009).  The gliding squirrel nests usually were several meters off the ground and located much lower from the point where branches originated (nearly 5–7 m), which may enable unobstructed access to the nest tree.  Also, trees with less canopy connectivity were occupied more when compared to trees with more canopy connectivity which might be a reason to avoid predation pressure as discussed above.  Gliding squirrels are predated by an array of mammals and birds (Taulman et al. 1998; Fan & Jiang 2009; Sun et al. 2009) and variables such as cavity height, entrance size, and condition of cavity trees are especially important factors for predator avoidance.  To decrease predation risks, gliding squirrels select high cavities with small entrances in live trees (Wesolowski 2002; Ruczynski & Bogdanowicz 2005; Mitrus & Socko 2008; Kosinski et al. 2011).

In the present study, it was observed that the Red Giant Gliding Squirrel typically had one or more feeding trees located adjacent to a nest tree.  During our study, it was observed that the individuals groomed initially after emerging from the nest and then glided to the nearest food tree for feeding unless the nesting tree is not a feeding tree.  In a study conducted on Grizzled Giant Squirrel Ratufa macroura in southern India, gliding squirrels preferred nesting in areas with higher food tree availability (Herlekar 2010).  In the Sierra Nevada Mountains, USA, Northern Gliding Squirrels Glaucomys sabrinus were reported to select specific tree species for nesting due to greater availability of hypogeal fungi food items associated with that tree species (Meyer et al. 2005).  Red Giant Gliding Squirrel preference of nesting in Altingia excelsa and Terminalia myriocarpa in the present study could be due to high abundance of the listed two tree species and larger height of these tree species in the study area. Additionally, the branching of Altingia excelsa occurs higher on the trunk versus other species, providing tall naked trunks which provide easier access to nest cavities.

Though we compared the present study to various studies with regard to nesting habits of the giant gliding squirrels, understanding forest composition and structure, habitat quality, and anthropogenic disturbance, frequency of use of nests by species, duration of use need to be studied for better understanding of the nesting preferences.  Also, from the present data, we cannot conclude the exact nesting preferences of the study species statistically due to smaller sample size.  Habitat management, however, aimed at conserving cavity trees may be needed to conserve gliding squirrels, and those cavities and cavity trees that they selectively use should be preferentially conserved (Suzuki et al. 2013).  Although our study indicates that large old trees of Altingia excelsa and Terminalia myriocarpa were typically selected, our small sample size has limited inference for making recommendations to forest management, however, it has to be noted that the species prefers old trees with natural cavities for nesting.  On the whole, stress on additional studies to examine long-term nest use by the species and to compare characteristics between nest trees and a random sample of forest trees is highly recommended to better understand the nesting preference of the species.

Table 1. Characteristics of nesting trees used by Red Giant Flying Squirrels in northern India during 2012-2013 (Data are mean±SE).

Table 2. Tree species observed nearby P. petaurista nesting trees and their absolute and
relative density and mean basal area in northern India during 2012–2013.

* Feeding trees (as per Krishna et al. 2015).

^# The data was not enumerated as the species did not lie in the vegetation plots.

Table 3. Comparison of nesting characters of Petaurista species globally.

For images/ figures –click here

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