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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