Where have all the sparrows gone?

When I was a schoolboy confined to a room with chicken pox, my mother found a simple way to keep me entertained - she left some food grain on the window sill every morning. The result was often the chirpy company of a host of sparrows throughout the day. The sparrow family in our neighborhood thrived for a number of years. But slowly that began to change as the sparrows abandoned the cities; for a while there were fewer of them to lay out food for, and eventually, none at all…

The House Sparrow (Passer domesticus) is one of the most widespread and abundant birds in the world. They are closely associated with man and his domestic animals. By the first few decades of the 20th Century the House Sparrow population had increased so much that it was considered an agricultural pest. But house Sparrow numbers over the last 30 years have fallen from 12 million pairs to fewer than 7 million pair. Assessing the causes of mortality in a bird population is itself not straightforward. For a species to decline there must be either a reduction in breeding productivity or in survival. In reality no single factor is likely to account wholly for a given population level. This is because reproduction and survival are seldom influenced by one factor alone, but by several, which may act independently or in combination. It is seen that more chicks were dying in the sparrows' second brood of the year, an observation that may help to explain the overall population decline. A number of hypotheses have been put forward as possible causes of the decline of House Sparrows in urban-suburban habitats. One of the main causes is predation by magpies, domestic cats, cabat cats, tanwy owls and Sparrow hawks. Among these cats kill most number of sparrows. The capture rates of birds were not affected by equipping cats with bells, possibly because birds rely largely on visual clues in predator avoidance behavior. Acting mainly through resources such as food, inter specific compitition is yet another factor that could limit House Sparrow numbers. An overlap in food and other resources provides the potential for competition because some of the resources removed by one species might otherwise have been available for a second .Thus individuals of a dominant species can greatly reduce the feeding rates of individuals of subordinate species. In this case house sparrows have to compete with other seed-eating larger birds such as pigeons, gulls and doves. Lack of holes suitable for nest sites on modern or renovated buildings has been proposed as a possible cause of the House Sparrow population decline. Sparrows used to build their nests below tilted roofs. With contemporary architecture making a clean sweep in cities, tilted roof became a thing of past and sparrows lost prospective nesting spots. Scarcity of food is also one of the reasons. The birds were used to peck at grain in backyards of homes where housewives cleaned paddy or wheat. Grain spills outside godowns or provision stores drew a lot of sparrows twittering over them. But now, with backyard cleaning virtually extinct, and with improved storage to meet EU regulations, polythene packaging taking over from gunny bags, there are no handy spills, and neither are there twitters. Many toxic chemicals are now added continuously to the natural environment, either as pesticides, industrial effluents or combustion emissions. Some of these chemicals are now regarded as important agents of bird population declines. Denis Summers-Smith's (recognized as a world expert on sparrows) theory was that the unleded fuel, believed to be eco-friendly, had harmful byproducts. The fuel uses Methyl Tertiary Butyl Ether (MTBE) as an anti-knocking agent. Along with byproducts of combustion, this kills small insects. Though adults can survive without insects in their diet, Chicks were more likely to starve if their diet contained a high proportion of vegetable material or ants, and less likely to starve if their diet contained a high proportion of spiders. Thus with fewer insects to feed on, the infant mortality rates of sparrow went up. It is also found that the concentrations of heavy metals such as zinc, cadmium and lead were higher in ill and dead nestlings than in healthy ones. House Sparrows may also serve as a reservoir of disease in urban and suburban areas. The infectious disease salmonella is common during winter and spring in free-living wild House Sparrows. In cases of fatality the birds show enlargement and congestion of the liver and spleen with liver, lung, muscle and skin abscesses.

In recent years, a number of studies has been conducted to find out the relationship between the increase in electromagnetic waves and the decrease in the number of sparrows. A positive correlation has been found between them and it is concluded that , these tiny birds are fast disappearing from cities "contaminated" with electromagnetic waves arising out of increased number of mobile handsets. It is also seen that sparrows are found to be disappearing from areas where mobile towers are installed. Scientists have also found very interesting difference in the birds behavior close to the phone antennae. Young birds died from unknown causes, and bird couples frequently fought while constructing their nests. Sticks fell to the ground, and the couple failed to make any headway. Some nests were never completed and the sparrows remained passively in front of the antennae. But these are all circumstantial evidences. Now we need to prove how it is exactly affecting the sparrows. Most probably this magnetic waves affect their central nervous system. Apart from this exposure to electromagnetic wave, several thousand birds die each year from collisions with telecommunications masts. Accidents happen mainly in fog, or bad weather, when birds might be using the earth's magnetic field for navigation, and could be seriously disoriented by the microwave radiation from telecommunication masts.

Thus it can be said that nest sites, cover, predators or disease can all restrict a species to only parts of an area where food is available, while predators and parasites can reduce rates of food intake and body condition, thereby enhancing the effects of food shortage. Therefore it must be acknowledged that any of the environmental factors that have been proposed as possible causes of the decline of the House Sparrow, could combine and interact as a joint limitation to the urban population. Nonetheless, one thing is clear, what has happened to the birds is a very sensitive indicator that the environment is changing. In recent times, sparrows are not the only birds whose number has decreased. We used to see a lot of bee-eaters, kingfishers, golden orioles and sun birds. There are hardly any around now. To stop this we have to take necessary steps. This includes reducing use of unleaded fuel. LPG can easily be used as an alternative. Also any measures that boost insect numbers in gardens should help nesting sparrows. Our smoky and unfriendly environment may be forcing birds to take wing and head elsewhere. The challenge is to arrest that, and to bring back some of the familiarity with the natural world that was common not so long ago.