Hi,
The difficulty, as indicated in the article below, is with detectability. If
you read the chapter in my book Bird Census Techniques (Bibby, Burgess, Hill &
Mustoe 2000), you will find the original North American schemes were quite
problematic, as are many others around the world.
This latest article is intriguing, as it makes a direct correlation between
traffic noise and detectability. Let's assume for a moment that we want to
understand changes in the environment and we use bird numbers as an indicator.
Changes in habitat density as well as traffic noise (through road development)
and a suite of other confounding factors can seriously affect the numbers of
animals we record. There are of course, methods that can deal with this but we
can't depend on just encountering birds in the manner that we do for atlas
work. I have raised this issue a number of times with Birds Australia
regarding the Atlas project. In its current form it serves a useful and
fundamental purpose but to have real benefit, it needs to be redeveloped and
render densities for different
habitats.
If we fundamentally underestimate bird numbers using such methods, then their
credibility is thrown into doubt. This is exactly what happened when the Royal
Society for the Protection of Birds started to lobby the UK government on
declines in farmland birds in the mid-1990s, leading to a move away from their
territory mapping method.
On a slightly different note, it is also fascinating to discover how much
traffic noise affects human ability to detect birds. Most birds and humans have
similar hearing shapes (we hear similar frequencies) but birds are altogether
poorer at detecting noise than we are. I've heard this used in impact
assessments to say that birds are therefore not as susceptible to noise
impacts. Not so. Birds are more dependent on sound and their inability to hear
each other quite so well is the reason why traffic noise has a big impact, as a
result of poor hearing ability. In studies in the Netherlands they have shown
levels only a few dB above background (approx. doubling of sound level) can
result in substantial loss of breeding productivity and even displacement.
Regards,
Simon Mustoe.
> Date: Sun, 30 Nov 2008 17:28:51 +1100
> From:
> To:
> Subject: [Birding-Aus] Bird Population Estimates Are Flawed, New Study Shows
>
> http://www.sciencedaily.com/releases/2008/11/081121080819.htm
>
>
> --
> John Leonard
> Canberra
> Australia
> www.jleonard.net
> ===============================
> www.birding-aus.org
> birding-aus.blogspot.com
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