Bird Numbers

To: Wynton <>, "" <>
Subject: Bird Numbers
From: Brian Fleming <>
Date: Sat, 26 May 2001 18:38:51 +1000
Wynton wrote:
> Hi Birders,
> Being a numbers man i could not resist giving some input re local bird
> lists.
> For about 25 years i have been recording birds at North Lake and Blue
> Gum Lake near Perth.
> At North Lake the total is 104 and Blue Gum is 72. The highest daily
> counts have been 55 at North Lake in Jan. and Feb. and 38 for Blue Gum
> Lake in Feb.
> This is expected due to the summer migrants and the westwards pull to
> the coast as the inland lakes dry out.
> The interesting relationship is that the total number of species is
> almost twice(sorry to get into accountant speak but both ratios
> are1.89 ) the highest individual count conducted when it is likely the
> max. numbers could be expected.
> This rule of thumb could prove very useful when time ( such as 25
> years! ) does not allow a very long and exhaustive survey to determine
> the total numbers of species. It is of course based on surveying the
> same area over and over and on a relatively small area based around a
> Lake.
> 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.
> Regards   Wynton
I would agree with this statement. I have been noting the number of
species seen at local parks here in the Heidelberg area (suburban
Melbourne with Yarra and wetlands) for about 30 years. The total score
for a walk round the local park is usually 28 to 32, say 30. (When I
started, early 1970s, it used to be around 35). But it's seldom the same
30 on successive days. The total number of bird species seen in our
local park over the year would probably be well over 60, and again would
vary from year to year, depending on continental and local conditions.

Anthea Fleming in Ivanhoe, Vic.
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