On Fri, Oct 03, 2008 at 10:00:27AM +1000, Andy Burton wrote:
> There seems to be a general acceptance in the Aust / NZ birding world
> that global warming causes migrant birds to arrive earlier.
> Why don't migrant birds arrive later?
There has been a good effort by people at Macquarie to analyze arrival
and departure dates of migrants in SE Australia, abstract here:
http://www3.interscience.wiley.com/journal/118575740/abstract
There does seem to be a trend across ecologically disparate species which
could plausibly be attributed to climate change but I don't think there
is enough data to be really convincing. Changes in numbers of birds
and observers can be major confounding factors. E.g. there is a strong
trend to earlier in the year for first Sydney observations of Koels &
Channel-bills but at least some of that is likely caused by increased
numbers of birds & observers. For some of the other species they look
at trends are inconsistent between areas. WT Needletails are arriving
significantly earlier in Canberra but there is no change in Sydney.
As to why, I don't think that is well understood, there is a review freely
available online here: http://www.int-res.com/articles/cr_oa/c035p037.pdf
and I'm sure there are plenty more recent papers.
Andrew
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