Bird Numbers

To: "birding aus" <>
Subject: Bird Numbers
From: "Philip A. Veerman" <>
Date: Thu, 31 May 2001 13:00:22 +1000
Whilst Andrew's comments are correct, it is more practical to do a graph of cumulative species recorded over time, as well as a graph of number of species that have been recorded on every survey as at the end of each survey. These together give a measure of both the likely potential and the number of species regularly present. My (soon to be available) report on COG's GBS demonstrates and describes these aspects in detail, using yearly blocks. Even after 18 years (1151 observer years of data), the graphs have not stopped changing. However after about ten years, the rate of change slowed down distinctly, so by now we are very close to a stable state to be able to estimate the number of species potentially present and the number of species that can be reliably found every year (as well as the the number of species can any one year is likely to record).
-----Original Message-----
From: Andrew Taylor <>
To: <>
Date: Wednesday, 30 May 2001 17:18
Subject: Re: [BIRDING-AUS] Bird Numbers

On Fri, 25 May 2001, Wynton wrote:
> I would be interested to see if this ratio is consistent with other =
> surveys as it could be used for conservation and other reasons to =
> estimate the total number of species based on only a few visits.

You may find it difficult to estimate the size of the eventual bird list
of an area, because the number doesn't exist.

I believe typically the list of birds recorded from an area will
continue to grow, with continuing observation, without bound.  Over tens
and hundreds of years the growth will come from observation of species
(vagrants) which occur only very infrequently in the area.  Theoretically,
over tens or hundreds of thousands of years growth will come from
speciation - the birth of new species.  Admittedly the extinction of
class Aves would end the growth.

In other words, if you lived forever, I'm saying that your local list
would never reach a limit and stop growing.  Although after a few
centuries the growth might be very slow.

Its actually fortunate that birdwatchers do not live thousands of years
- species boundaries already provoke enough arguments without having to
consider the much more problematic notion of chronospecies.

You could, of course,  estimate the number of species present within
an area at a given time or within a given period.

If you are really interested in this stuff try looking at ecology
textbooks - biologists have been considering methods to estimate or
compare species richness and related concepts from limited samples for
at least 60 years - and still seem to be inventing new ones.

Andrew Taylor

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