By comparison, I present the following extract from my book: Canberra Birds: A
Report on the first 21 years of the Garden Bird Survey that gives info from
Canberra.
The range of number of species recorded on individual charts (that is a 100
metre radius site for a year or part thereof), is broad. This is out of a
sample size of 1316 observer years of data. This is partly influenced by the
number of observer-weeks. The lowest score was on five charts that recorded
only 13 species, up to one that recorded 99. Only 12 charts had over 75
species. The mean, mode and median of species (i.e. number of records) per
chart are 41.16, 36 & 39 (respectively). There is a clear impression, that the
variation relates to the combination of effort put in, habitat involved and
experience level of the observer. There is little doubt that observers differed
in their interpretation of the instruction (which varied on the different chart
versions) to include birds within the 100 metre radius area. This surely played
a role in the variation of number of species (records) per chart.
When considering species recorded at an individual site, surveyed on anything
from one to 21 years (sample size 294), this is a broad spread and varies from
13 to 135 species and broadly increases with number of observer-weeks. Most
sites in Canberra had less than 70 species but the nice thing is that even
sites going continuously for 21 years are still adding one or two species a
year towards the end of that 21 year period. Ten of the 294 sites had 100 or
more species.
Philip
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