Alan and all,
I assume that the data involves species which migrate from the tropics to
more temperate zones on one side of the equator, rather than those species
which migrate between the northern and southern hemispheres. In other
words, the birds are spending more time away from the tropics. The
suggestion is that this provides biological evidence of global warming.
Cheers
Carol
At 11:40 AM +1000 21/9/03, Alan Gillanders wrote:
>Greetings All,
>
>Reading Henry Nix' presidents column in the latest 'Wingspan' caused me to
>consider this issue. If we are seeing migrants earlier and they are
>staying for longer and this is being observed in the northern hemisphere,
>there are at least three possibilities.
>
>1. Some species are choosing to spend more time in the northern hemisphere
>while others in the south.
>
>2. Some individuals or populations within species are changing their
>length of stay in each hemisphere.
>
>3. The departure and arrival times are becoming broader in range within
>species or migrants in general. ( This is like a combination of 1 & 2 but
>is different to each and maybe should be separate points for migrants in
>general and at the species level.)
>
>Does anyone have data on this issue which illuminates my darkness?
>
>Regards,
>Alan
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