On Thu, Dec 07, 2006 at 09:12:06PM +1100, Peter Ewin wrote:
> Species rarely establish this way I would have thought (Cattle Egret
> and Spotted Whistling-duck maybe are the only cases I can think of)
> so it is unlikely to be impacting on native birds if released.
Any species found across Wallace's Line, e.g. Lewin' Rail, Barn Owl,
Black Kite has made a sea journey and so presumably has any species with
a congener on the other side of Wallace's Line, e.g. Rainbow Beeeater,
Dollarbird, Australian Bustard & Metallic Starling. The direction
of some journeys is debatable but a significant part of our avifauna
arrived that way. How many arrived as individuals - rather than in a
conspecific group is an interesting question. Thats over millions of
years of course - a great many more immigrants must die without progeny
or at least extant descendants.
If a a wild bird arrives under their own power I'd regardthem as native.
Although you can certain make a case for estirpating a bird clearly
dependent on human environmental modifications like Cattle Egrets.
I certainly won't be standing on the rock fending off Fiordland Penguins.
Andrew
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