Hi David and others,
I am afraid that the Asian house gecko can't be placed in the category
of "self-introduced". Their success here is related to human-assisted
arrival, particularly by ships into northern Australia. Populations have
been shown to radiate from ports.
Further, this species is no longer confined to urban dwellings, it has
spread into bushland (i.e. around Darwin etc) and has the potential to
displace/outcompete native gecko species. A similar situation is
occurring here in Brisbane.
There are also now cases where the Asian house gecko has been recorded
feeding on native skink species.
Best regards, Pete Kyne
Brisbane, Queensland
-----Original Message-----
From:
On Behalf Of Greg & Val
Clancy
Sent: Friday, January 11, 2008 9:33 AM
To: Birding-aus; david taylor
Subject: what is a feral
David,
Canada Geese are not in the came category as the other vagrants that you
mention. They were introduced into New Zealand and therefore are quite
different to the Northern Pintail, Northern Shoveler etc. These
vagrants
are mostly northern hemisphere breeding species and are unlikely to
breed in
Australia, even if more than one was to arrive. However if they did
establish it would be a natural event and not a human induced
introduction.
If they stow away on ship, like the House Crow, then that is a different
situation again, as they are human assisted. A native New Zealand bird
that
found its way without human intervention to Australia would not be
treated
as feral. The Kelp Gull has done just that and I don't hear anyone
suggesting that the Kelp Gulls in Australia are feral. The Cattle
Egret,
Monarch (butterfly) and Asian House Gecko are in a different category
again - self introduced species that only occur because of human
modification to the natural environment in Australia. They probably
don't
pose the same sort of threat to natural ecosystems as do the Canada
Geese as
they have exploited human made, and otherwise vacant, niches. In fact
Cattle Egrets may provide some protection to nesting Great, Intermediate
and
Little Egrets by increasing colony size and therefore improving security
from predation. Cattle Egrets feed in different microhabitats to the
other
egrets and therefore don't compete directly for food.
Greg Clancy
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