Richard -
At 11:06 PM 23/08/03, you wrote:
What are the scientific reasons/theories for these complex and frequently
very long migration patterns, ie what are the present (or past - assuming
that it is now genetically-acquired behaviour, which may not any longer
actually be necessary) survival advantages of making such a flight, over
the obvious disadvantages. Does it date back to a previous age when the
advantages were more apparent, or are the present advantages of migration
still so great that the behaviour continues to be truly necessary?
With regard to the migratory waders or shorebirds, and further to Tony
Crocker's response; there are examples of migratory species splitting into
migratory and non-migratory forms. One of the more obvious ones in
Australia is the Red-capped Plover splitting off from Kentish Plover
stock. Another (presumably somewhat older) split is Inland Dotterel from
Eurasian Dotterel. It seems to have happened around the world more with
the plovers than the sandpipers - maybe because of less specialised feeding
methods and equipment in the former. However, see the scattered
distribution of isolated taxa of woodcocks and NZ snipe in the Asian and
Australasian regions - and the Prosobonia sandpipers of the Pacific. Did
these derive from populations of migratory ancestors in which some
individuals stopped migrating?
Cheers,
Hugo
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