Getting scientifically useful data from bird lists

[Julian Robinson <>]

Statisticians and those involved in analysing COG's various atlas data
might be interested in an article in latest Decision Point with the title
of "Bird lists can reveal underlying trends".  It
discusses research that addresses the difficulties of using
variable-effort presence lists as a basis for meaningful measurement of
decline and increase.  Maybe this research will allow COG to get
more info from the less systematic lists  in the database? 
i.e. not so much the BOCG or woodland surveys since they are meant to be
"known effort", but the random lists submitted. 
Interesting reading anyway.

 http://www.aeda.edu.au/docs/Newsletters/DPoint_38.pdf  page
3

...
But the analysis was possibly more important
in
demonstrating that a Bayesian List Length Analysis allows
you to model changes in prevalence over time using
species lists that were collected with variable effort.
?We?ve demonstrated that List Length Analysis is useful
for modelling relative abundances from species lists, as we
were able to detect declines and increases,? says Szabo.
?What?s more, estimating the magnitude and
certainty of
those changes was straightforward.
?Further, we can calculate the probability that there has
been a decline of a given magnitude. The list length
method proved very robust for moderately common
species. We discovered that this method has the capacity
to alert us to species declines and lays the groundwork for
using historic datasets that previously were of only limited
value.
?What?s more, this method allows ecologists to calibrate
more recent datasets of different quality and to plan how
dense and intense future sampling networks should be in
order to detect predetermined levels of decline.?
These measures are useful to managers who may
have to
establish whether a threshold of decline has been exceeded
to warrant a listing of a species as
threatened.
...

The best way to detect changes in the
abundance of birds
is still through properly planned systematic surveys, where
birdwatchers visit the same sites and count birds in the
same way at regular intervals (such as the 20 minute/2
hectare count method of Birds Australia). But this new
AEDA research has demonstrated that even the humble
bird list can by useful in revealing trends over time.
?For the casual bird watcher this means that all those lists
are gold, especially old lists,? says Hugh Possingham, a co
author of the research. ?Anybody can enter
their bird lists
in Birds Australia?s ongoing atlas [http://www.birdata.com.
au/homecontent.do] which provides an invaluable longterm
repository for future analyses. This means that the
humble bird watcher may one day provide the essential
data that drives environmental accounts and hence
government policy!



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