On the Kerala coast the annual and daily range of temperature are small, normally remaining within the range 21 0C to 32 0C. At the base of the hills the temperature may be slightly higher and lower than these limits. Up on the Western Ghats the climate varies with altitude and aspect but is generally similar to that of a moist temperate region. In winter the temperature may drop to freezing at night, and rise to 20 0C during the day.
Despite these variations one feature dominates climate in the region and that is the monsoons. Most of the rain in the region falls between June and September during the southwest monsoon season. During this time cool, moisture-laden winds from the Indian Ocean bring heavy, intermittent rains. Typically, the monsoon begins in Kerala in late May or early June and moves north and west to extend over northern India by the end of June. On reaching the Western Ghats the air rises and cools and the moisture condenses, providing abundant rainfall along this range. The monsoon begins to retreat from the northwest at the beginning of September and usually withdraws, completely by mid-October. Rain continues, however, in the southern peninsula, and in the southeast around half the annual rain falls between October and mid-December. This is brought by winds coming from the northeast during the northeast monsoon. The amount of rain varies from year to year, especially over areas of poor rainfall, where it may be as little as 30 to 40 per cent of a normal year. Even when the total monsoon rain in an area is about average, it may fall over a very short period, bringing floods and drought in the same year.
The bird habitats of southern India can be roughly divided into forests, scrub, wetlands (inland and littoral), marine, grasslands and agricultural land. There is overlap of some habitats, for example mangrove forests can also be considered as wetlands, as can seasonally flooded grasslands. Many bird species require mixed habitat types.
There is a great variety of forest types in the region. Tropical forests range from coastal mangroves to wet, dense evergreen, dry deciduous and open thorn forests. The forests of the region are vitally important for many of its birds, including both globally threatened and restricted-range species.
Tropical deciduous forests once covered much of the plains and lower hills of the sub-continent, including moist and dry sal and teak forests, riverine and dry thorn forests. Several widespread species endemic to the subcontinent are chiefly confined to these forests, including the Plum-headed Parakeet, which has a preference for moist deciduous forests, and the White-bellied Drongo, which favours open, dry deciduous forests.
Scrub has developed where trees are unable to grow in the region, either because soils are poor and thin, or because they are too wet, such as the edges of wetlands or in seasonally inundated floodplains. Scrub also grows naturally in extreme climatic conditions, such as in semi-desert. In addition, there are now large areas of scrubland in the region where forests have been over-exploited for fodder and fuel collection or grazing
Wetlands in the region are abundant and support a rich array of waterfowl. As well as providing habitats for breeding resident species, the subcontinent's wetlands include major staging and wintering grounds for waterfowl breeding in central and northern Asia. The region possesses a wide range of wetland types distributed almost throughout, including freshwater and brackish marshes, large water-storage reservoirs, village tanks, saline flats and coastal mangroves and mudflats. Small water storage reservoirs or tanks are a distinctive feature in India. Aggregations of those tanks provide important feeding and nesting areas for a wide range of water birds in some places.
Some grasslands still exist, especially on the eastern side of the Western Ghats.
Seabirds in the region compromise mainly gulls and terns, with a few truly pelagic species (e.g. petrels and shearwaters).
The region is remarkable for the abundance of birds in agricultural habitats in many areas, as a result of non-intensive agricultural systems and low levels of hunting and persecution. Shrikes, Indian Roller, Common Hoopoe, parakeets and birds of prey, for example, can appear abundant on road and rail journeys. This is changing though, as farming becomes more intensive and higher levels of pesticides are applied.