Mammals of northeastern India : an updated checklist

A systematic review was carried out to prepare a checklist of the mammalian species of northeastern India. The region is located between two prominent biodiversity hotspots, Himalaya and Indo-Burma. Though it is only 8% of the country, it supports almost half of the country’s total wild flora and fauna. Ongoing developmental activities such as the construction of roads, electrification, and mining in and around the wildlife habitats have threatened the survival of many species of wildlife. A lot of literature has been checked to understand the status and distribution of wildlife in the region and the present manuscript is prepared from existing literature. A total of 267 species representing 11 orders and 38 families from the region have been reported. A state-wise updated list of species along with their status as per IUCN, WPA (Wildlife Protection Act) of India, 1972 and CITES has been provided which is intended to serve as a baseline data for further research in mammalian fauna of the region.


INTRODUCTION
The northeastern region (NER) of India (21.57°-29.30°N & 88°-97.30°E) consists of eight states, namely, Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, Sikkim, and Tripura, covering an area of 262,185km 2 (NEDFi 2020) (Figure 1). NER shares 5,182km international border with China in the north, Bhutan in the north-west, Myanmar in the east, Bangladesh in the south-west, and Nepal in the west. The region constitutes approximately 7.9% of the geographic area of the country. Almost two-third (approx. 70%) of the area is hilly comprising most parts of Arunachal Pradesh, Meghalaya, Mizoram, Nagaland, Sikkim, about half of Tripura, one-fifth of Assam, and nine-tenth of Manipur (NEDFi 2020). Physiographically, the region can be categorized into eastern Himalaya, the Patkai, and the plains of the mighty Brahmaputra Valley, the Barak Valley, and the Imphal Valley. The climate of the region is predominantly subtropical with hot and humid summers, severe monsoons and mild winters (Jain et al. 2012). The rainy season generally begins from the end of March and continues till September. Annual average rainfall varies 1,577-6,002 mm, and temperature ranges 5-40°C with mean relative humidity remaining between 70% and 85% throughout the year (Jhajharia et al. 2009).
The region has large areas of rainforest that supports the habitats of diverse biota. The region supports a wide variety of flora and fauna due to its diverse habitats and favourable climate. Numerous research groups, including the Zoological Survey of India (ZSI), the Bombay Natural History Society (BNHS), and the Field Museum of Natural History (FMNH), have carried out systematic surveys in different regions in NER, including the mammalian fauna.
Taxonomic accounts of different mammalian fauna have been carried out by various researchers. Hinton & Lindsay (1926) described the distribution of mammals in northeastern India (Report No. 41, Assam and Mishmi Hills), Ellerman & Morrison-Scott (1951) published checklist of mammals in India and Palaearctic region, Ellerman (1961) emphasized the detailed records of rodents in India, Myanmar, and Sri Lanka. Corbet & Hill (1992) reviewed the distribution of Indo-Malayan mammals including mammals in northeastern India. Molur et al. (2002Molur et al. ( , 2005 reviewed the status of Chiroptera and the non-volant small mammals in southern Asia. These are important records of mammals in the region. At the beginning of 21 st century, ZSI documented mammals of the region under various state series reports such as by Das et al. (1995) for Meghalaya, Bhattacharya & Ghosh (2002) for Tripura, Mandal et al. (2005) for Manipur, De et al. (2006) for Arunachal Pradesh, Mandal et al. (2007) for Mizoram, Chattopadhyay et al. (2006) for Sikkim, and Srivastava et al. (2006) for Nagaland. All these are significant contribution as they mostly published reports from the field study with detailed verification. Many recent studies (Kumar 2011;Kumar 2014;Kakati & Kabra 2015) reported the records of mammals in particle areas while mammals of southern Asia by Srinivasulu & Srinivasulu (2012), mammals of northeastern India by Choudhury (2013), the checklist of mammals of India by Sharma et al. (2013) are the records of the whole region. The book "Mammals of northeastern India" by Choudhury (2013) is the most valuable for the taxonomic and geographic distribution of the mammalian species in the region. Most recent records like distribution list of the bat fauna of Assam by Boro et al. (2018), distribution of Mammals in the Indian Himalayan region by Kamalakannan et al. (2018), mammals in Arunachal Pradesh by Kumar (2018), bat fauna of Meghalaya by Saikia et al. (2018), mammalian fauna in Meghalaya by Lyngdoh et al. (2019), review of the bacular morphology of some Indian bats by Srinivasulu et al. (2020), and some other recent discovery of mammals in the region shows the importance to update the mammalian records of the region. In addition, taxonomic revisions especially of the lower mammalian orders are one of the reasons for updating of the checklist.

METHODS
The present checklist is based on a review of existing literature on the mammalian fauna of northeastern India. Literature sources include online repositories, like Biodiversity Heritage Library, DeLCON, Google Scholar, PubMed, ResearchGate, and offline journals, articles, and books. Taxonomic arrangement of the mammals is primarily based on Srinivasulu (2019). Comments are added for the presence of more than one subspecies in the region to clarify their distribution in the respective states. Also, IUCN Red List database, Schedules of Indian Wildlife Protection of India, 1972 (IWPA), and appendices of the Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES) were checked to verify the current conservation, and protection (national and international) status of the species.

RESULTS AND DISCUSSION
The current checklist enumerates a total of 267 mammalian species under 139 genera, 38 families, and 11 orders within the political boundary of northeastern India. A state-wise breakup revealed the presence of 166 species in Arunachal Pradesh, 161 species in Assam, 113 species in Manipur, 169 species in Meghalaya,116 species in Mizoram, 119 species in Nagaland, 154 species in Sikkim, and 74 species in Tripura (Table 1). Among the 267 species, the order Chiroptera represents highest number of species (87), followed by rodents (60). These two orders jointly constitute 54.8% of the total mammal diversity of the NER. The order Carnivora is also diverse in the region having 46 species, followed by the orders Artiodactyla (26), Soricomorpha (18), Primates (13), and Lagomorpha (9); while the rest of the orders contain one or two species (Figure 2).
Based on recent taxonomic revisions (Benda & Gaisler 2015;Saikia et al. 2017), Pipistrellus pipistrellus, Pipistrellus kuhlii, and Philetor brachypterus are omitted from the present checklist. Similarly, species such as Hipposideros ater, Ochotona nubrica, and Scotozous dormeri are indicated as doubtful in the checklist due to lack of proper evidence. Of the 267 mammal species in the region, three species, namely, Assam Mole Shrew Anourosorex assamensis, Namdhapa Flying Squirrel Biswamoyopterus biswasi, and Manipur Bush RatHadromys humei are the endemic to the region. Five extinct species from the region, namely, Red Deer Cervus elaphus, Cheetah Acinonyx jubatus, Banteng Bos javanicus, Sumatran Rhinoceros Dicerorhinus sumatrensis, and Javan Rhinoceros Rhinoceros sondaicus are also included in this list. Red Deer was earlier recorded from Sikkim which is now locally extinct there but present in other regions of India; while other species are considered to be extinct from India. Species such as Pteropus giganteus, Barbastella leucomelas, Plecotus auratus, and Miniopterus schreibersii have been substituted with Pteropus medius, Barbastella

Threat Status
The current conservation status of the mammals in the NER as per IUCN Red List of Threatened Species 2020, CITES 2019, and IWPA 1972 are presented in the checklist ( Table 1). Analysis of IUCN Red List categories   Table 2.
The northeastern region of India harbours numerous wild mammalian fauna (Images 1-8). Many new species are recently reported which are important to the incorporated in the regional account, especially taxa like Chiroptera and Rodentia. Previous studies were mainly focused on large-sized mammals; however, the recent discovery of a few mammals from the region indicates that additional studies require which might help to detect other undiscovered species.