Avian habitats face numerous threats
There has been a lot of change in the physical environment of our country in the past five decades, notes eminent ornithologist Zafar Futehally. "In the early 1950s, in our gardens in Andheri, Mumbai, there were jungle babblers (
Turdoides striatus), magpie robins (
Copsychus saularis), golden orioloes (
Oriolus oriolus) and many more birds. Now there are nothing but crows in the same area," he rues.
Why are birds becoming fewer? The reasons are many and often complex. Habitat fragmentation and chemical contamination have proved hazardous for those that have a short range and also a short life span like Jerdon's courser (
Rhinoptilus bitorquatus; see box
Small range, greater threat). Other birds like the great Indian bustard which require specific habitats are threatened when their habitats get degraded (see graph
Bird killers).
Chemical scourge in wetlands
Wetlands are among the main habitats of birds in India about 20 per cent of birds depend on them. These aquatic areas are under serious pressure. During a 1999 nationwide sarus crane census, for example, many participants noted that wetlands were polluted with domestic and industrial waste, pesticides and fertilisers. "The problem gets compounded because no state in India includes wetlands in its land use statistics. So unprotected wetlands are vulnerable to land use change," says Ritesh Kumar of Wetlands International, Delhi.
Lalita Vijayan of the Salim Ali Centre for Ornithology and Natural History (
sacon), Coimbatore, notes that a study on wetlands conducted by her organisation revealed that "fish in wetlands had residues of heavy metals and pesticides, some at levels far above those prescribed by
who."
The Indian skimmer (
Rynchops albicollis), once common in the river systems of north India, is one bird whose habitat has become unsafe because of chemical contamination. It is categorised as vulnerable in
iucn's Red List. "This bird's requirements overlap dangerously with those of people," says A R Rahmani of
bnhs. Experts such as him say increased use of pesticides in cultivation of fruits like melons on the banks of large rivers is reducing the breeding sites for the skimmer.
In the Red List, the status of the falcated duck (
Anas falcata) and black-tailed godwit (
Limosa limosa) changed from 'least concerned' in 2002 to nearly threatened in 2006; that of the sociable lapwing (
Vanellus gregarius) and the spoon-billed sandpiper (
Eurynorhynchus pygmeus) changed from vulnerable in 2002 to critically endangered and endangered, respectively, in 2006. Significantly, all these are water birds.
Drugged
The chemical bane doesn't just mean pesticides. Consider the case of the white-backed vulture (
Gyps bengalensis). Decline in the bird's population was
![Down to Earth](http://cdn.downtoearth.org.in/image/20070415/43.jpg)
first documented in a breeding colony in Keoladeo Ghana National Park, Bharatpur, Rajasthan, by
bnhs researchers in 1997. Numbers of breeding pairs in the park fell steadily through the late 1990s, and by 2000 there was none left. Later studies confirmed that the decline extended across northern and central India.
Surveys confirmed that the major ecological factors usually held as responsible for a population crash--food and nest site availability--were not an issue. But it was only in 2004, that a
Nature (Vol 427, published online, January 28, 2004) study incriminated the anti-inflammatory drug, diclofenac--commonly administered to livestock whose carcasses are food for the vulture.
![Down to Earth](http://cdn.downtoearth.org.in/image/20070415/46.jpg)
There was much debate and conservation groups called for the immediate withdrawal of the drug from the market. The Indian government banned the drug in 2006.
A recent study published in the journal
PLoS Biology (Vol 4, No 3, January 31, 2006) has proposed a substitute for diclofenac--meloxicam. When administered to vultures, it did not produce any visible negative effects. Experts, however, say the larger chemical problem remains unadressed.
The shotgun
Birds are not safe in other aquatic habitats either. The protected Chilika lake in Orissa, for example, is fast becoming a death trap for migratory birds. According to an estimate, in 2003 more than 200,000 birds fell to poaching. "Poaching is rampant in almost every part of the lake. The poachers very often use chemicals. The birds are sold in cities like Bhubaneswar," says Ram Behera, an anti-poaching activist.
In Asia, exploitation of birds for human use is the second most common threat to 50 per cent of all threatened species. About 70 per cent of these are consumed and 30 per cent end up in bird markets. Many fear that the bird trade threatens many more species, even those with wide ranges. There is documentary evidence of trafficking in 450 out of the 1,300-odd Indian bird species. The ones most traded are rose ringed parakeet (
Psitttacula krameri), black-headed munia (
Lonchura atricapilla) and rock pigeons (
Columba livia).
The climate factor
Another threat is rivers getting flooded during breeding season nests in colonies on low sandbanks are destroyed. This is commonly attributed to deforestation in watersheds of major rivers and consequently rapid runoff. But another reason cannot be ruled out changing climate and consequent glacier retreat and change in monsoon patterns. "During a three-year study along Sikkim's Teesta valley, we found some birds had moved to altitudes higher than where they were found earlier," says Vijayan. "Other probable impacts of climate change can be found in the Andaman Islands. Here, sea level rise has affected coastal wetlands and the birds they host."
Exotic danger
Exotic species render habitats (both grasslands and wetlands) unfit for birds. Water hyacinths are a major problem in wetlands and lakes. The growth of lantana around Dehradun district was one factor responsible for the disappearance of the Himalayan quail (
Ophrysia superciliosa). Invasive species are particularly threatening for short-range species. For example, the domestic goat has affected regeneration of vegetation and imperilled nesting sites of the narcondam hornbill (
Aceros narcondami) in the Andaman and Nicobar Islands.
But it's not only invasive plant and animal species. Non-native bird species have become invasive for many native bird species. The rock pigeon was introduced into many parts of the world, including India, from Europe for food and as game. These birds live in human habitations such as farmlands and buildings, and are known to transmit a variety of diseases to humans, domestic poultry and wildlife.
In the mid-19th century, house sparrows were introduced into the
us from Europe to alleviate the homesickness of settlers from the old world. These adaptable birds spread their wings across North America and in many cases outcompeted native birds for nesting sites and resources. According to data collected by The Birdhouse Network--a citizen-science project initiated by Cornell University--in 2003, house sparrows account for 43 per cent of all species that take over nest boxes meant for native birds.
Similarly, the myna (
Acridotheres tristis), which Indian farmers regard as a friend because it feeds on crop pests, is loathed as a pest in Australia.Introduced in the country in 1862 to control sugarcane pests, it destroyed fruits and grains, and aggressively competed with native wildlife species for nesting hollows.