In the forests of Sikkim and Arunachal Pradesh, there is an occasional rustling high up in the canopy. One looks up to catch glimpses of brown and chestnut through the leaves. If it is a particularly lucky day, we may see a large furry rodent launch itself into the air, extending the webbing between its legs to glide downhill, a long bushy tail following behind. This is a giant flying squirrel.
Ready for a challenge? Click here to take our quiz and show off your knowledge!
A recent study modelled the distribution of two giant flying squirrels from the Eastern Himalayas using reports of sightings and environmental data. It found that only a fraction of the squirrels’ currently designated range harbours suitable habitat for these mammals; furthermore, this habitat is expected to drift westwards and break into small and isolated patches due to climate change. These findings raise alarms about the future of these poorly studied gliding mammals, calling for more research that can inform their conservation.
Enigmatic gliders
There are over 50 species of flying squirrels in the subfamily Sciurinae. These mammals glide between trees by stretching parachute-like membranes along their bodies to generate lift. Adapted to an arboreal life, flying squirrels play an important role in pollination and seed dispersal.
“We know about flying squirrels found in the Americas, Europe and Japan,” says Nandini Rajamani, who leads the Sciurid Lab at the Indian Institute of Science Education and Research, Tirupati.
Ready for a challenge? Click here to take our quiz and show off your knowledge!
“The diversity of flying squirrels is highest in the tropics. Unfortunately, the number of studies on flying squirrels here has been very low,” says Rajamani, about the lack of information about their habitat requirements and distribution. “In the more diverse regions, we somehow know less,” she adds.
“Tropical forests are tall and multi-layered and nocturnal research is very challenging in landscapes like these because you simply don’t see these animals,” says Rajamani. “All it takes is one glide and they are gone.”
Namdapha Tiger Reserve. Tropical forests have a complex structure, making it difficult to observe and study flying squirrels high up on the trees. Image by Rohit Naniwadekar via Wikimedia Commons (CC BY-SA 4.0).
An additional challenge in studying flying squirrels is the species conundrum. Many of the larger flying squirrels belong to the genus Petaurista, a taxonomic puzzle with a dozen or more species distributed across Asia. “They are very polymorphic, so you see incredible variability in coat colour even within a single species,” explains Rajamani.
“Northeast India and the Himalayas have several flying squirrel species, but we know very little about their phylogenetic relationships, ecology and even their distribution,” Rajamani says.
Predictions of distribution and decline
The eco-spatial modeling study assessed the Hodgson’s giant flying squirrel and the Bhutan giant flying squirrel which are distributed in the Indo-Burma biodiversity hotspot. The two species vary in their elevational and geographic occurrences, though they overlap in the Eastern Himalayas of Sikkim and Arunachal Pradesh in India, Nepal, and Bhutan. Based on habitat and climate data from specific locations where each of these flying squirrels occurs, the researchers, built machine learning models to predict habitat suitability within the broad distribution range for each species. They used these models to forecast habitat suitability for future climate scenarios. The researchers used projections from two different climate models, one assuming intermediate greenhouse gas emissions and the other considering very high emissions. For both these scenarios, they used climate predictions for 2041-2060 and 2061-2080 to model habitat suitability for flying squirrels. Finally, the team used model predictions to assess how habitat shape and connectivity would vary because of climate change.
“Species distribution modelling tells us about the ecological envelope of a species based on existing knowledge,” says Imon Abedin, a Ph.D. student at Bodoland University, Kokrajhar and one of the lead authors of the study. “It tells us if a habitat is similar to where the species is known to be present. As a first step, the results can help us identify areas to start surveying.”
The Bhutan giant flying squirrel (Petaurista nobilis) is distributed across the borders of Bhutan, India and Nepal. A recent study modelled its habitat suitability using known occurrence records and forecasted species distribution under climate change. Image by Umeshsrinivasan via Wikimedia Commons (CC BY-SA 3.0).
The study shows that only a small fraction (4%-14%) of the currently known range of these species, as designated by the International Union for Conservation of Nature (IUCN), harbours suitable habitats. Presently, areas in Nepal and the India-Nepal border are important for habitat connectivity for the Hodgson’s giant flying squirrel, whereas the borders of Arunachal Pradesh and Sikkim with Bhutan are important corridors for the Bhutan giant flying squirrel.
The model’s forecasts of habitat suitability under different climate change scenarios show significant declines from the present. For the Bhutan giant flying squirrel, which is found in isolated montane forests, the models predict habitat declines of >85% in two to six decades. For the Hodgson’s giant flying squirrel, which has a broader elevational range in evergreen forests, models show variable predictions (10%-80%) of habitat loss. Both species, however, show a westward shift in their geographic range because of climate change, with fewer and more isolated patches of suitable habitat.
The study’s authors, however, point out that evaluating species distribution models trained using few or unreliable species records can be challenging.
“Reports of species presence are likely to be few and far between for narrowly distributed cryptic species. What is used as input is key,” adds Rajamani. On-ground surveys can help researchers verify species presence in predicted areas of habitat suitability and gather additional occurrence locations that can iteratively improve the model.
No flying squirrels without trees
These predictions are alarming, given the existing threats of habitat loss and degradation in the Eastern Himalayas. “Some of it is because of conversion to cash crop monocultures, illegal logging in low elevation forests, and infrastructure development,” says Aparajita Datta, a scientist at the Nature Conservation Foundation who studies plant-animal interactions in the Eastern Himalayas. Land-use changes have led to habitat loss in the region, but their effect on biodiversity can vary based on the type of change. Shifting cultivation receives the blame for a lot of forest loss in this region, but recent research shows that it creates a mosaic of landscapes that can be better for biodiversity compared to complete conversion to monoculture, says Datta.
“Some flying squirrels are quite adaptable and can thrive in modified habitats such as fruit plantations,” says Rajamani, based on observations in the Western Ghats. “But flying squirrels in the genus Petaurista need tall forests, and the absence of tall trees spells habitat loss,” she adds.
The modelling study calls for field surveys for flying squirrels where model predictions can help researchers prioritise areas for monitoring. Maps of habitat suitability can even be used to assess the conservation status of species as has been done for the clouded leopard in Southeast Asia and the Himalayas, Abedin says. However, on-ground conservation efforts can be challenging for flying squirrels, as they often spill over international boundaries and cooperation across borders is needed to conserve habitats from crashing under climate change.
This article originally appeared on Mongabay. Read the original article here