Use of Foreshore Acacia nilotica Stands by Migratory Waterfowl
in
the Tanks of Bangalore, India: A Habitat Manipulation Prospect
S. SUBRAMANYA
HPHT Scheme, University of Agricultural Sciences,
Bangalore-560 065, India
Man-made irrigation tanks are the major form of wetlands in the Deccan Platen of India. These tanks have been created by building dikes across low areas to impound monsoon run-off. The water, thus accumulated, is used for irrigating rice crops in the down-stream. These tanks can be visualized as shallow basins with concentric zones of varying water depths with the deepest region close to the bund (embankment). During winter, the bird population in these tanks reaches up to 26,000 birds (x= 1,017, SD=3,474, n=96), consisting of 67 waterbird species (87% migrants) depending on the size of the tank. Five species of migratory ducks, namely Anas crecca, A. querquedula, A. acuta, A. clypeata, and Aythya ferina and a goose (Anser indica) congregate along the shoreline in the foreshore region of the tank for resting and indulging in body-maintenance activity. Overhead flights of four birds of prey, namely Haliastur indus, Circus aeureginosus, Falco perigrinus, and Aquila clanga disturb these congregations of ducks. Under the social forestry program the foreshores of the tanks are being planted with Acacia nilotica, a tree species tolerant to waterlogging. Nineteen species of waterbirds, including the five species of ducks utilize these foreshore stands as refuge during feeding, resting, and body-maintenance activities. The present study reports the effect of overhead flights of predatory birds on duck congregations in the foreshore regions in tanks with and without A. nilotica stands.
The frequency of visits by predatory birds was significantly higher in tanks without foreshore stands of A. nilotica (P<0.001). Following disturbance, the ducks moved into deeper water and on 11% of the instances ducks abandoned the tank.
A management plan of establishing several raised sandbars of varying dimensions planted densely with A. nilotica in different regions of the tank is suggested. In addition to reducing the disturbance to migratory ducks by predatory birds, the planted sandbars are expected to reduce the possible human disturbance to birds.
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