The Biligiris are
charnockite hills, covered with
tropical dry broadleaf forest, part of the
South Deccan Plateau dry deciduous forests ecoregion. The forests range from scrub forests at lower elevations, degraded by over-use, to the tall deciduous forests typical of the ecoregion, to stunted shola forests and montane
grasslands at the highest elevations, which exceed 1800 meters. The forests form an important
wildlife corridor between the
Western Ghats and the
Eastern Ghats, linking the largest populations of
Asian elephants and
tigers in southern India. The most conspicuous mammals in the BR Hills are the herds of wild
elephants. The BR hills is the only forest east of the main Western Ghats mountain ranges in the central southern
peninsula to harbor these pachyderms in large numbers. The forests were the study area for R. Sukumar, a scientist who studied the elephants of the area in the early eighties. A recent (2017) survey has revealed the presence of 62
tigers in this sanctuary. The forests are well known for many
gaur, the largest
bovines. BR hills are a good place for viewing many other large and small animals. There are about 26 species of
mammals recorded in the sanctuary. The other mammals include
sambhar,
chital, the shy
barking deer which are quite common here and the rare
four-horned antelope. Carnivores include
tigers,
leopards,
wild dogs, lesser
cats and
sloth bears and among
arboreal mammals two species of
primates and three species of
squirrels including the
giant flying squirrel are recorded. A recent (2017) survey of tigers by
DNA analysis of
scat samples has revealed 62 tigers, although the number may be more. 254 species of birds have been recorded in the BR hills. These include the enigmatic southern population of the
white-winged tit (
Parus nuchalis), a specimen of which was collected by R. C. Morris and is now housed in the Natural History museum at Tring. A recently discovered species is the microhylid frog
Microhyla sholigari, named after the
Soligas, an indigenous tribe that inhabit these hills. ==Threats==