Chemical catastrophe

Pesticides can render birds sterile. Migratory birds can lose sense of direction. The recent history of the world is full of many such examples ess

Published: Friday 15 January 1999

Chemical catastrophe

Pesticides are essentially products of urbanisation and agricultural modernisation. As cities began growing, lands -- once home to birds -- were put to intensive agricultural use. To increase crop yield, farmers used pesticides liberally. Owing to the formidable gap between their intake and effect, it took scientists more than half a century to realise that these chemicals were being far from benign in their effects.

Silent wings
Today, scientific literature is full of instances of the adverse effects of pesticides on birds. Take ddt , once the most popular pesticide, for instance. Its most use occurred in California where, between 1949 and 1957, it was applied just thrice in Clear Lake to control gnats. It not only eliminated its intended targets, but brought the population of Western Grebes ( Aeschmorphorus occidentalis ) from a thousand breeding pairs to zero as well. It then went on to suppress the bird population for years to come.

l There are many such instances of organochlorines and endocrine disrupters affecting birds. In the 1980s, experts discovered that since 1950, sex ratios in certain population of North American gulls and the Caspian Tern (Sterna caspia ) became skewed, favouring females. Homosexual pairings accounted for less than 10 per cent of the breeding pairs on Santa Barbara Island, California, between 1972 and 1980.

These pairs were associated with abnormally large number of eggs laid. After much research, scientists found the unbalanced sex ratio to be the result of feminisation of male embryos through exposure to ddt and its metabolics. The most disproportional sex ratios and the highest incidence of homosexual pairing in Western Gulls occurred in a local ddt 'hot spot' in Los Angeles, California.

l In the mid 1980s Black-billed magpies (Pica pica ) suddenly suffered local population declines for no apparent reason in many parts of the us . However, extensive research revealed the true story: the birds were suffering from contamination by a organophosphate pesticide called femphur. The pesticide was usually used to control warbles or fly larvae in cattle. Poured on backs of cattle, it kills the larvae in the cattle's bloodstream. It was an effective way to eliminate the insects. The only problem was that it remained active long after its application.

The magpies were its first or primary victims. It claimed Red-tailed Hawks ( Buteo jamaicensis ) that fed on the magpies as its secondary victims. Soon, reports of many such primary and secondary bird deaths poured in from all parts of the country. Research soon proved that as a pour-on, femphur would pose severe risks to the birds and it was described as a chemical with "extreme toxicity" ( Ecological Applications , Vol 7, No 4).

l In migratory birds, organophosphates can interfere with their ability to orient themselves in the proper direction for migration. When consumed, these chemicals are stored along with the birds' fat reserves. During the long migratory flights, the fat reserves are used up and the chemicals are 'liberated', disorienting the birds.

l The Californian condor, once common in California and its suburbs, lost a formidable percentage of their population, and by 1982, there were just 20 left. Now, none exist in the wild and only 50-60 in captivity. Accumulation of pesticide content in body tissues, lead poisoning through gun-shot carcasses and poisoning through baited rodent pests have been forwarded as some of the primary causes of this drastic decline.

l The us 's national bird and a long-standing symbol of power and elegance, the bald eagle, now classified endangered, continues to fall prey to endocrine disrupting chemicals through their food sources such as contaminated fish. As in all their victims, these chemicals led to premature cracking of the bald eagle egg shells.

l The uk , like its transatlantic neighbour, suffers from similar afflictions. The uk 's indigenous grey partridge is a bird of arable landscape. Nick Sotherton, research manager for the Farmland Ecology Unit of the uk -based Game Conservancy Trust, writing in Pesticide News , says that in the last 40 years, these birds have suffered drastic population losses. These chicks feed on insects. Pests, contaminated by pesticides and herbicides, are believed to be the main factor in chick losses.

l Reports of bird deaths due to pesticide intake pour in from all corners of the world. In another such instance, the uk reported a drop in the last 20 years of more than 75 per cent in song thrush population, found mainly on its lush farmlands. The culprits -- an easy guess -- are pesticides used against slugs and snails -- food thrushes depend on.

l In Vienna, a massive bird mortality accident occurred in Tuleca County from late December 1991 to early January 1992. Thousands of birds died, and an autopsy of 943 bodies revealed carbofuran, a maize seed dressing, as the cause of death.

l South Africa ( sa ), too, has reported several pesticide-related bird deaths. "Cranes and other bird species are being affected by extensive use of these chemicals," reported the sa newsdaily Antidote in 1993. "Farm workers in Overberg, South-Western Cape, scatter grain soaked in pesticide to kill guinea fowl.

This has proved to be a major factor behind numerous blue crane ( Anthropoides paradiseus ) deaths," it reported. The paper listed the organochlorine dieldrin as one of the major killers.

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