Thursday, 22 March 2012
Modern Life and Old Enemies (Cats and Crows) Reduce Sparrow Populations
Song of the sparrow
Mar 20, 2012:
The World Sparrow Day, being observed today, reminds us of the need to welcome sparrows back into our cities. There are many reasons for the disappearance of this tiny bird, including a change in farming practices, architecture and lifestyles, writes Antony P U
The house sparrow (Passer domesticus) has become a rarity over the years due to various reasons. Noisy and gregarious, this cheerful exploiter of man’s wastefulness is a Red List species today. Human-altered habitats, particularly farm areas, are preferred by them. House sparrows are granivorous and 96 per cent of the adult diet is made up of livestock feed, plant materials like grain, fruit, seeds, and garden plants. G arbage, bread crumbs and refuse from fast-food restaurants can support sparrow populations in urban habitats. The current worldwide distribution of this bird is a result of this commensal relationship of it with humans.
As agriculture and human civilisations expanded, house sparrows experienced a correlated and massive expansion in range and numbers. Due to their abundance, ease to raise and general lack of fear towards humans, the house sparrow has proved to be an excellent model for many avian biological studies. To date, there have been nearly 5,000 scientific papers published with the house sparrow as the study species.
They are persistent and fairly intelligent. House sparrows are aggressive and social, both of which increases their ability to compete with most native birds. Sparrows do not migrate. While house sparrows are tolerant of disturbance by humans, they can in no way be considered tame. Their success lies in their ability to exploit new habitats, particularly those influenced by humans.
House sparrow numbers have fallen significantly since they peaked in the 1920s, when food and wastes from horses furnished an unlimited supply of food. One question of considerable interest concerns the catastrophic house sparrow population declines in several urban centres of the world.
Possible reasons proposed are changing agricultural practices such as a shift to monoculture crop plantings and sealing grain stores to reducing access and spillage, increased pollution, use of herbicides/pesticides and its impact on food sources. There are various other causes for dramatic decrease in their population, one of the more surprising being the introduction of unleaded petrol.
Denis Summers-Smith who is recognised as a world expert on sparrows presumes that the unleaded 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. The insecticidal nature of the byproducts makes the food for those birds feeding on insects scarce. Though adult sparrows can survive without insects in their diet, they need them to feed their young. With fewer insects to feed on, the infant mortality rates of sparrows went up.
Reduction in areas of free growing weeds or a drop in the number of badly-maintained buildings, which are important nesting opportunities for sparrows, have also contributed to the disappearance of the bird. The widespread use of chemical pesticides in farmlands has resulted in the killing of insects on which these birds depend. Seed-eating birds like sparrows have to depend on soft-bodied insects to feed their young ones.
Predation by crows and cats
The other possibility could be increased predation by crows and cats. Crows have grown in number as a result of garbage accumulation in the city. Changing lifestyles and architectural evolution have wreaked havoc on the bird’s habitat and food sources. Modern buildings are devoid of cozy nesting sites for sparrows like ventilators, eaves and crannies. This, coupled with disappearing home gardens, are playing a part in the sparrow’s disappearing act.
My casual observations in selected areas of Bangalore to correlate the abundance of the bird with architecture of the buildings, commercial activities going on, human population and their lifestyle, etc convey that sparrows are not totally extinct from Bangalore, but there are still areas where significant populations of this bird exists. Some such areas that I came across in the southern and eastern parts of Bangalore are the Rajendra Nagar slum in Koramangala, Anjaneya Temple Street and AR Colony in Adugodi, S G Palaya, Ejipura, New Tippasandra in Indira Nagar, wholesale fruit market in Huskur, etc.
A moderate number was observed in churches like Infant Jesus Church in Vivek Nagar and St. Mary’s Basilica in Shivajinagar. They were active even in the vicinity of various small old temples buildings in Adugodi and Ejipura. It is very interesting to note that sparrows are mostly the companions of poor and middle income groups in slums and old villages within the city where people have still retained their thatched houses and their old lifestyles and food habits. Shops and other establishments like flour mills, grocery shops, where they store grains in open bags, etc, invite more sparrows in slums and villages. Even the old-styled electric poles with all the wires strewn out haphazardly form ideal roosting places for the birds here.
Architecture makes a difference
Not even a single sparrow was noticed in any of the posh, planned residential layouts like Koramangala, Jayanagar, BTM Layout, Indira Nagar, etc. or even in the outskirts of Bangalore with organised apartments. Living in close proximity with humans, sparrows used to build their nests below tiled roofs. With contemporary architecture making a clean sweep in Bangalore, tiled roofs have become a thing of the past, and sparrows have lost many a nesting spot. Also, the birds were used to pecking at grain in the backyards of homes where people 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 polythene packaging taking over from gunny bags, there are no handy spills, and neither are there twitters.
In recent times, sparrows are not the only birds that have moved out from cities. In Bangalore, one used to see a lot of warblers, barbets, bee-eaters, kingfishers, golden orioles and sun birds. Today, most of them have given way to scavenger birds like crows, mynahs and kites which feed on the large amount of garbage generated in the City. Our smoky and unfriendly cities may be forcing birds to take wing and head elsewhere. The challenge is to arrest that and to bring back some of these little winged beauties that were common not so long ago. This requires giving up on luxurious lifestyles that allow harmonious living with other species. The World Sparrow Day reminds us of this need.
Posted by Stephanie Jones at 05:22