Like Peter Ormay, I think Martin’s work on this is interesting
and valuable - including his note on ‘tight-arrival’
migrants in this months Gang-gang. However, I sometimes think it can be misleading
to focus, like the figurative eagle-eyed contributor to The
Times, on the ‘first arrival’ of migrants - in
relation to so-called partial migrants. For one thing it diverts
attention from the true migrants, whose movement variation might conceivably reflect
climate shift and not just local food availability.
Clearly enough, the GBS records movement of birds through the suburbs.
Thus there is clearly a seasonal element to the garden appearance of
Grey Fantails for example. With such birds there is quite likely (a) an
altitudinal element and/or (b) a vegetation element eg to/from woodlands.
Taking ‘Canberra’ as including its woodlands, it
seems to me that insufficient work has been done to be certain of the annual movement
pattern of birds that are present in our area during Winter, although in much
reduced numbers: eg Noisy Friarbird, Dusky Woodswallow, Olive-backed
Oriole (remember Graeme Clifton’s report in July). The second BA
atlas, with the first COG atlas, is a start. Other movers that can be
present in Winter in reasonable numbers include Welcome Swallow, Black-faced
Cuckoo-shrike, Rufous Whistler, Yellow-faced and White-naped Honeyeaters and
Fan-tailed Cuckoo. I have difficulty with the idea that any of those
birds have ‘just arrived’ when they are reported in Spring.
The term ‘partial migrant’ seems to me to be
confusing shorthand. It might suggest that some members of a population migrate
only a short distance, or that some members do not migrate at all. With
regard to the species in question it may be that Canberra is properly regarded
as at the fringe of the Winter range and a few members of more southerly
populations range about our area.
To me the ‘true migrants’ among our land birds are
those that are absent from South-east Australia in Winter, eg Koel, Bee-eater,
Dollarbird. Significantly, it is these that seem to have ‘tight’
arrival schedules (which makes all the more interesting the ‘early Koel’
reports). I would also include the Painted Honeyeater, which you can set your
calendar by at Cocoparra.
From: martin butterfield
[
Sent: Monday, 1 September 2008 5:04 PM
To: COG-L
Subject: [canberrabirds] Dusky Woodswallows
This afternoon a flock of about 6 Dusky Woodswallows were
hawking along Whiskers Creek Road (about 200m outside my GBS site).
In terms of GBS observations this coincides nicely with the expected upturn in
number of observations. A graph is attached: note that this shows the raw
number of observations rather than the F% value, since the two lines are
similar and this one is slightly simpler to plot. I have also extended
the graph to show that the observations (after the initial 'surge") are less
consistent than was the case for the Noisy Friarbird.
