Yesterday afternoon through to after dark I was observing the behaviour of waterbirds from the bird hide at the Waterbird Refuge, Sydney Olympic Park. Water levels at the wetland are quite low at the moment, so waterbird numbers in the early part of the afternoon were also quite low. However, from about 5 pm onwards the wetlands began to fill up with birds as they came in to roost for the night.
The main purpose of this email is to report briefly on the reactions of the waterbirds to helicopters flying low (300-400 m altitude over the wetland). During the day, the waterbirds were habituated to nearly all the disturbances around them, such as the noise from car/truck traffic flows along nearby Bennelong Parkway, Hill Road and Homebush Bay Drive, helicopters flying directly over the wetland or above the aforementioned roads, low-flying planes approaching Sydney Airport, and distant background noise from rock concerts associated with the Big Day Out Event at the nearby Sydney Showground.
The only noticeable reaction to daytime disturbances occurred when the occasional pedestrian using the nearby cycle/pedestrian path stopped and observed birds from the open shoreline, or when there was thunder & lightning. On these occasions, some species took flight and sounded alarm calls before settling back on the wetland (e.g. Black-winged Stilts), whereas others just swam or waded into deeper water near the centre of the wetland (e.g. Chestnut Teal, Grey Teal and Red-necked Avocets).
With respect to the thunder & lightning, it appeared that the birds became flighty in response to the thunder rather than the lightning. The storm was several kilometers away, so there was a gap of several seconds between the lightning and the sound of thunder.
With respect to helicopters, waterbirds did not react noticeably to helicopters flying overhead or nearby during the day. However, in the one hour that I stayed at the wetland after dusk, two helicopters flew directly over the wetland while the birds were roosting. Both helicopters had their pilot lights on, but these lights were not strong enough to illuminate the wetland. So, there was clearly a temporal change in the sensitivity of these birds to helicopter disturbance. It would be interesting to know if this was because they were roosting at the time of the disturbances, were disturbed by the helicopters’ pilot lights, are more sensitive to disturbances when it is dark, greater densities of birds on a wetland are more reactive to disturbances, or a combination of all of these things.
I’d like to hear of other peoples’ observations of background disturbances that waterbirds in urban environments have become habituated to, what background disturbances never lead to habituation, and whether there are any other observations of temporal sensitivities to background disturbances. |
