On Thu, 21 Aug 1997, Debra Sparn wrote:
> This begs the question (and I think that I know the answer, but I will
> leave it to those of you who are more knowledgeable than I), why do
> introduced birds do so well, when so many native birds are so hard to save?
Most introduced birds don't do well. In Australia and I presume elsewhere
a great number of accidental and deliberate bird introductions fail.
We should be also careful about judging the success of an introduction
on human scales. Some introductions might take hundreds or thousands
of years to fail.
Some introduced species now have large populations and significant
ranges in Australia. Personally, I place the reasons in three
categories.
a) They successfully exploit human-modified habitats. Much of Australia
has been modified in the last two hundred years creating new habitats.
Species that have exploited these have increased their range
and numbers. For example, Galahs were found in modest numbers
along northern bird courses, they are now abundant through most of
Australia.
Species are not randomly chosen by man for introduction. Species which
successfully exploit human-modified habitats outside Australia are
presumably much more likely to be introduced to Australa. Why can these
species successfully exploit human-modified habaitats - perhaps like the
Galah this is "coincidence" , their existing adaptions suit the new
habitat or perhaps because they have adapted to human-modified habitats
elsewhere (e.g. Europe) which have existed for longer periods than
Australia.
b) The "shock of the new" - they may possess adaptions whose utility lies
in their novelty in Australia. For example, they may possess a predator
avoidance mechanism which is very successful until Australian predators
adapt.
c) They possess adaptions of which no analog has appeared in Australian
species and these adaptions will have long term utility in "natural"
Australian conditions.
It seems to me category (a) accounts for most, perhaps almost all,
of the success of introduced birds in Australia.
Andrew Taylor
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