Last Friday afternoon (23 January 2009) 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. For instance, only 16
Chestnut Teal and 2 Grey Teal were on the wetlands during the count
conducted from 1530 to 1550 hrs. By the time of the count conducted from
1930 and 1950 hrs there were 219 Chestnut Teal and 156 Grey Teal. The last
count was conducted from 2025-2050 hrs the total Chestnut/Grey Teal count
was 395 birds (by this time it was too dark to distinguish between some
individuals of these two species).
There were few migratory shorebirds on the wetland, presumably because there
was very little water in the wetland, but there were lots of Black-winged
Stilts and Red-necked Avocets. Maximum counts for these two species were 67
Black-winged Stilts and 43 Red-necked Avocets.
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.
Stephen Ambrose,
Ryde, NSW
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www.birding-aus.org
birding-aus.blogspot.com
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