re: Crakes and Rails

Subject: re: Crakes and Rails
From: (Roger Jaensch)
Date: Thu, 13 Nov 1997 18:02:49 +1000
     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.
     Roger Jaensch
     Wetlands International - Oceania
     GPO Box 636 Canberra ACT 2601 Australia
     tel:  +61-6-2500779     fax:  +61-6-2500799

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