I agree with the gist of comments by Lawrie Conole (12 Nov) regarding
behaviour of the three crake species found in southern Australia.
As demonstrated by Tony Palliser (13 Nov) in regard to Lewin's Rail,
calls can be helpful in locating crakes and rails that might otherwise
be overlooked.
As an example, my recent investigation of a lignum/coobah swamp in the
Bulloo Lake system (SW Queensland) is typical of what I have
experienced around Australia at different times. The swamp lacked any
exposed mud in the section that I explored and thus could have been
written off as crake-less. However, Australian Spotted Crakes gave
excited yelps and cackles from within lignum shrubs as I waded around
in the 0.3-0.5 m deep water, needing no enticement to call. On two
occasions, Spotless Crakes gave their diagnostic rattle calls, but
also were not seen.
Two separate Baillon's Crakes were seen at the Bulloo swamp: they were
walking on floating mat of duckweed (Azolla) at the edge of lignum
shrubs, but were not heard calling. (Which recalls a Baillon's seen on
algal mat around the stems of a spreading coobah shrub in 2 m deep
water in the woodland part of Nongra Lake, NT: this species is
versatile!) The point here is of course that lack of calls does not
necessarily imply lack of birds, particularly for less vocal species.
Regional differences seem to apply. In south-western Australia
generally Spotless Crake appears to be the most abundant of the three
crakes. I suspect Baillon's Crake has a higher (relative) reporting
rate in eastern Australia than in most of SA or WA.
Then there is the complication of seasonal movements. There is a view
(Atlas, 1984) that Baillon's Crake moves north during April-September,
whereas the case for regular movements by the two other species is
less convincing. All three seem to be opportunistic in exploiting
ephemeral habitat. This seems especially true of Australian Spotted
but that conclusion may be biased because the species is relatively
vocal and conspicuous.
In conclusion, I believe it is extremely difficult to draw valid and
consistent conclusions about the relative abundances of crakes and
rails. Perhaps systematic searches over an extended period (at least 5
years) may yield some useful results/trends but most data sets not
generated this way could be misleading.
regards,
Roger Jaensch
Wetlands International - Oceania
GPO Box 636 Canberra ACT 2601 Australia
tel: +61-6-2500779 fax: +61-6-2500799
email:
|
