The House Sparrow was indeed one of the commonest urban birds in India when Salim Ali was a boy. The recent years have witnessed a perplexing decline in the number of the House Sparrow in many parts of the country (and elsewhere abroad). It is indeed a matter of concern that the population of House Sparrow has dwindled. However, the paranoia set-off by the news media has only resulted in an outburst of ill-founded speculations about the possible causes of the decline and that the decline itself is signalling an imminent ecological disaster.
Loss of tree cover, changing architecture of human habitation that has deprived the House Sparrows of nesting sites, excessive use of pesticides, lack of traditional granaries, grocery shops and storehouses that permit gleaning of grains by birds, air pollution and electromagnetic radiation2 have all been identified as the culprits. The paranoia about vanishing House Sparrows reminds me of the alarm bells that desperately rang nearly 20 years ago of ‘declining’ amphibian populations.3 The alarm bells succeeded in establishing the Declining Amphibian Population Task Force (DAPTF) as a specialized and dedicated unit within the IUCN. No sooner, global warming, UV-B radiation, outbreak of a dreaded fungus, pesticide poisoning, over-harvest (including biological collections), etc. were listed as probable causes for the decline of the amphibians3–5. Scientific investigations did support the view that one or more of the listed causes adversely impacted amphibians throughout the world, although the intensity of a specific cause varied locally.
Exclusive focus on amphibians did provide a number of new insights about their biology and ecology. It also led to the discovery of species that had not been described by taxonomists earlier. Unfortunately, however, the quest for finding ‘new’ species of amphibians soon overshadowed the primary purpose of DAPTF that in some parts of the world, especially in India and Sri Lanka (biodiversity hotspots), biologists have shifted their focus from attempting to understand and mitigate the root causes of amphibian declines to merely collecting, naming and renaming species6. The shift in focus has been justified as a ‘mission to document the species before they are lost’7.
In the absence of sound data on population dynamics and geographical distribution, it has not been possible to assert that there have indeed been declines in amphibian numbers anywhere in India. Lack of scientific information has also stood in the way of attributing apparent declines to any specific environmental cause popularly cited. A study carried out in 2002–03 in the Western Ghats, in one of the most highly pesticide-impacted tea landscapes, identified loss of habitat as the primary local threat to amphibian species5. The study brought to light major gaps in our understanding of amphibian ecology.
Ecology, especially of anurans, requires field studies of the habitat requirement, availability and use by a species throughout its life history. It is embarrassing to learn that the habitat requirement of even the most common species of amphibian is not fully understood8. Having learnt important lessons from the study of amphibians, I wish to caution that the pursuit to correlate environmental factors such as electromagnetic radiation with declining populations will sooner or later lead to intrusive experiments involving the House Sparrow and other birds.
Electromagnetic radiation is naturally emitted by the sun and reaches the earth in millions of measurable units every second. Radio waves and microwaves have been used in telecommunication for a long time. Radio-telemetry has become increasingly popular in wildlife biological research. Telecommunication involves the conversion of audio-visual (and ultrasound) signals into electromagnetic signals that travel at the speed of light.
If these signals are deleterious to birds, they should be so to a number of other animals that share urban landscapes with humans. Why must the House Sparrow be vulnerable when crows, pigeons, owls, mynas, bats and geckoes have not succumbed to electromagnetic radiation that is attributed to telecommunication? The decline of the House Sparrow can be better explained if some of the more obvious attributes are analysed. For this we may first consider its lineage. A rather diverse group of birds representing at least 8 genera are called sparrows9–11. The species of sparrows pertinent to the discussion are those belonging the genus Passer and with the exception of the House Sparrow, all are subtropical and temperate in distribution.
At least six species of Passer have been reported from the Indian subcontinent. Besides the House Sparrow, these include the Spanish Sparrow (Passer hispaniolensis), Sind Sparrow (P. pyrrhonotus), Eurasian Tree Sparrow (P. montanus), Russet or Cinnamon Tree Sparrow (P. rutilans) and Dead Sea or Afghan Scrub Sparrow (P. moabiticus)9,10. The Spanish Sparrow is a winter visitor to northern India. The Eurasian Tree Sparrow that is generally a northern species, has a small resident population in peninsular India10. Sind, Russet and Dead Sea sparrows are not known in peninsular India.