Birds are one of the most valuable bioindicators and biomonitors in an ecosystem. The population levels of birds, their breeding practices and habit changes are being studied in a number of countries across the world. While a number of these studies are aimed at the conservation of birds, a substantial number are aimed at understanding the effects of pollution. And perhaps providing an early warning system on the possible fallouts. A clear example of this is the story of the ban on ddt in the us. Birds of prey were declining, and there was increased incidence of eggshell breakages as a result of the thinning of shells. This led to observation of the effects of ddt on wildlife, and its eventual identification as an environmental contaminant.
Essentially, birds are important cogs in the working of the ecosystem. Some species of birds, for example, are the pollinating agents for flowering plants and fruit bearing trees. Also, insectivorous birds are natural pest and insect controllers. They play an important role in maintaining the balance of the ecosystem by consuming pests that prey on plants. It is in this role that they are particularly useful agents for farmers. In a space where the right balance between birds and their environment is maintained, farmers would spend much less on pesticides and insecticides. This also reduces the rate of soil degradation.
This aspect, in particular, has fascinated me. I have been studying the relation between birds, pests, insects and pesticides in Malda district, West Bengal, for years. It is evident that the use of pesticides and insecticides reduces the role of our insectivorous avian friends. What is less studied in India is the role pesticides play in directly or indirectly killing pollinator and insectivorous bird species. My studies in Malda have led me to conclude that there is a direct link between increased use of pesticides and increased incidence of bird deaths.
Mango trade is one of the most important businesses in Malda. The district is famous for the quality and taste of its many varieties of mangoes -- gopalbhog, amrapali, khirsapati, langra, fazli. Mango production depends on temperature, seasonal rainfall and proper maintenance of flowering trees. In Malda, the flowering season begins in November-December, and goes on until June-July. In these eight to ten months, traders at every level need to maximise their profits. The health of these trees, therefore, becomes a secondary concern. The only prevailing plan is that of short-term gain; to sell the fruits to the next prospective buyer at the highest possible profit. The fact that a large number of birds die during these months, especially during the mango-harvesting season, goes virtually unnoticed.
Insects and small birds that feed on the sap of mango blossoms either die instantly or become drowsy during the spraying of pesticides. I witnessed many such instances in the mango orchards in Malda during this season. There were also a number of instances where small and medium-sized birds fed on dead insects covered in a film of pesticides. These died within the space of a few hours after the spraying operation was complete. If these birds consume even a few insects, they become drowsy and cannot fly, falling an easy prey to stray dogs and cats.
Year after year, I recorded the recurrence of this phenomenon during the pesticide-spraying season. The indiscriminate use of pesticides has also caused the quality of mangoes to decline over a period. The popular Malda mangoes are today smaller in size than they were, and they don't quite taste the same. Over the last few years, the production of mangoes has declined, and traders are beginning to explore other areas of business. There is a hypothesis that this could be the long-term effect of sustained use of pesticides.
My studies, though, have been centred on birds, and I have recorded about 21 bird species that have been falling prey to pesticides in this area. These include: common iora (Aegithina tiphia), green bee-eater (Merops orientalis), small minivet (Pericrocotus cinnamomeus), dusky warbler (Phylloscopus fuscatus), red-vented bulbul (Pycnonotus cafer), red whiskered bulbul (Pycnonotus jocosus), common tailor bird (Orthotomus sutorius).
If no action is taken now, there will soon be very few bird species left in Malda. The effect of pesticides on birds also gets one wondering about what effect it could have on other animals, and the human population, of the area. Meanwhile, as we concern ourselves with saving birds from poaching, habitat loss and illegal trade, what are we doing about these silent killers?
Arunayan Sharma is an environment development researcher based in Malda