Subject: Re: vagrancy
Date: Dec 14 09:39:44 1995
From: Stuart MacKay - stuart at animal.blarg.net


Dennis wrote:

> Whether the normal slow flux of bird ranges can deal with
phenomena such as
> global warming will be interesting to see. Birds should be able to
> certainly handle it a lot better than salamanders, for example.

Blackcaps (sylvia whatever - my bird books are all packed away)
have dramtically shifted their wintering range in Europe in the last
15 years or so. Bird that used migrate south and east to winter in
Italy have changed to south and west taking them into the southeast
UK, The Netherlands, Belgium and France. Back home in northern
Scotland we used to judge how good the autumn migration was by the
number of "blackcap days" we had - sadly no longer. While not
unusual there are hardly any to be seen in recent years.

It is believed that local climatic change has been the triggering
factor. Whether this is as a result of global warming is hard to
say. However it demonstrates the resilience of some species.

My personal musings are that vagrancy and reverse migration
consigns / condemns a portion of the population to speculative
migration. Should conditions in the species habitats start to
change radically it may be possible that birds wintering or even
breeding outwith their normal range may flourish. Whether it is
genetic or a symptiom of genes is hard to tell.

The blackcap is a good example of changes in wintering area. For
breeding range changes, in the late 1970's and early 1980's there
was a lot of colonisation of Scotland by species which used to breed
in southern England as the European populations moved northeast.
Red-backed shrike and wryneck in particular, though only wryneck was
successful. In South Africa both swallow and common sandpiper
(similar to spotted sandpiper) have started breeding - this is only
6,000 miles outwith their normal breeding range !!! They do winter
there however.

I think there are a few major surprises for scientists as the world
starts to warm up. Personally I think that species will be able to
deal with it - since they have undoubtedly been through it all
before - however the rate of change will take a pretty significant
toll, though I doubt it will lead to lots of extinctions that some
people predict - ever the optimist.

A good example of the staying power of species was shown in a
recent edition of Science News. Apparently eggs of pond plankton can
survive complete dessication for 2-300 years and successfully hatch
once conditions become favourable.

Makes ya think don't it !!!

Stuart - T minus 17 and counting .........
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