Re: Parrot distributions

["Karen Bayly" <>]

On Fri, 9 Oct 1998,  wrote:

> It's clear that the ranges of lots of species are not static, and that
> human-induced changes to habitats will influence changes to bird
> distributions, as well as more direct causes such as escaping captive birds
> and deliberate introductions.  What is not so clear is how fluid those
> distributions are, were or would be in the absence of human interference.
> However, given the highly variable climate across much of Australia (in the
> longer term as well as seasonally), the high proportion of nomadic species
> in our overall bird population and the fragmented ranges of many species/
> "superspecies", "natural" range fluctuations might have been an important
> part of the ecological picture.  Maybe we sometimes take for granted a
> greater degree of ecological stability in pre-European times than was
> really the case?

I've also wondered about this.  I've often heard people comment that Sulphur-crested  Cockatoos and Rainbow Lorikeets have increased in the Sydney region.  However, I  have been reading the journals of James Cook, Joseph Banks, Arthur Phillip, and  various other earlier settlers or visitors (including Charles Darwin), and these birds  appear to have been quite common in the late 1700's and early 1800's.  It is possible  that they had decreased in numbers over the past 150 years and now are building up  to previous levels (although proving this in the scientific meaning of the word would  be difficult).

In general we tend to look at changes in population distributions of native birds over  very short time periods  - often less than 100 years - in which the effects of previous  or current human interference may still be strong.  Such time periods may be too short  to reflect the real population dynamics of a given population, particularly long-lived  species, and rarely adequately reflect the effects of variables such as climate  fluctuations.  We so often have no reliable baseline data against which we can  compare distribution changes.  At best, we may find some information in historical  documents and through Aboriginal knowledge, though often we have access to  neither.

As Jack Krohn noted, some species obviously have benefited from human-induced  changes to habitat etc. to the exclusion of other species.  However, our  lack of  knowledge about pre- and early-European Australian species distribution raises some  issues about how we judge what birds (or any other animal or plant) should be in what  region and in what abundance, especially when we are considering either culling or  reintroduction programs.  

While I have no solutions as to how we can get better baseline data, a greater  awareness of how little information we have on which to base many of our  conservation decisions, may go a long way to helping us make wiser choices.



***************************************************
Karen L. Bayly
Ecology Lab
School of Biological Sciences
MACQUARIE UNIVERSITY  NSW 2109
Phone: 61 2 9850-8191 or 61 2 9850-9441
Fax:   61 2 9850-8245
Email:  OR