canberrabirds

RE: Grey Butcherbirds in gardens??

To:
Subject: RE: Grey Butcherbirds in gardens??
From:
Date: Fri, 18 Feb 2005 16:24:36 +1100
Thanks Philip for that explanation. I don't get to COG meetings so it is hard 
for me to get books. The explanation of competition reducing grey butcherbirds 
I think could be a factor. However, currawongs and kookaburras are common down 
the coast (eg Ulladulla and Malua Bay) and in Sydney where butcherbirds are 
also common. I would say kookaburras are more common in those areas whereas 
currawongs may be less common. I like Geoffrey Dabbs explanation the best, I 
hope he doesn't mind me mentioning it, but he implies Canberra's lack of 
reptiles are the reason 'The Atlas notes that the low GB numbers have been 
linked to the city's poor lizard fauna and refers to Roberts CBN 14(2): 34'. 
This makes most sense to me. It may also have something to do with habitat or 
predation by cats.
A dramatic increase of grey butcherbirds in the last 3 years cannot be 
explained by changes in competition, but could be explained by changes in the 
legislation on cats with curfews and tougher compliance, less people keeping 
cats and more keeping them inside. Changes in cats and habitat (maturing of 
bushes and trees) may have also led to an increase in lizard numbers over the 
same period. 


Benj Whitworth 

-----Original Message-----
From: Philip Veerman  
Sent: Friday, 18 February 2005 4:14 PM
To: ; 
Subject: Grey Butcherbirds in gardens??

Benj and all: See this Extract from my book: "Canberra Birds: A Report on the 
first 21 years of the Garden Bird Survey" as follows as usual most issues have 
been addressed:

Grey Butcherbird Cracticus torquatus
This is a common species in major east coast cities, yet it is rare in 
Canberra. This would suggest that it is not the urban environment itself that 
causes the scarcity. In our area it occurs in woodland and along the 
Murrumbidgee river corridor. Maybe it is the competition from the abundant Pied 
Currawong that impacts adversely on this bird (see also the Laughing Kookaburra 
text). Records are mostly of isolated individuals and not many have repeat 
observations. So the bird passes through, rather than stays in the urban area. 
Numbers are much higher from February to June, than July to January. This may 
reflect dispersal during the non-breeding period. Its distribution suddenly 
increased from an average of 4.47% for the first 18 years to 10%, 18% then 22% 
for the last three years, which created the huge recent abundance increase.
Graphs on page: 103, Rank: 102, A = 0.00310, F = 6.21%, W = 5.1, R = 0.303%, G 
= 1.02.

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