At 09:41 PM 4/6/98 +1000, David McDonald wrote:
>Also .. we need a debate on recording simply presence/absence vs abundance. I
>was surprised to hear, recently, that presence/absence was being seriously
>considered. Hasn't the experience with the Australian Bird Count demonstrated
>the huge advantage of assessing abundance?
>
Hi David,
The interesting lesson we learnt from the ABC Project is that we probably
didn't need to count birds to get a relative measure of abundance.
The sample size was so large (over 2,000 sites), that seasonal and relative
changes in distribution and relative abundance of species was reflected in
reporting rates. For instance, if a grid block (say 10-minutes in size) had
50 ABC sites, then at Time A (a particular month, season or year) 40 of
these sites (80%) may have had Species X. If at time B, Species X had been
recorded only 10 of these sites (20%), then one may assume that it has
decreased in abundance in that grid block. This is assuming that observer
effort and detectability of the species remains relative constant in Times
A & B. A similar principle can be applied to geographical comparisons of
relative abundance.
***********************************************************
Dr Stephen Ambrose
Research Manager
Birds Australia (Royal Australasian Ornithologists Union)
Australian Bird Research Centre
415 Riversdale Road,
Hawthorn East,
VIC 3123.
Tel: +61 3 9882 2622
Fax: +61 3 9882 2677
Email: S.Ambrose <> (at work)
<> (at home)
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