Choosing a species with a defined winter range and analysing changes in
numbers and the location of the boundary might give an indicator of more
"global" temperature range. However indicator species cannot be chosen until
the effects of global warming on a given geographical region are known. For
example, some climate models predict that western Europe will become colder
and wetter as a result of increased global temperatures. I would expect more
continental climates, ie North America to be a bit more "predictable" than
maritime climates such as western Europe, however the changes caused by global
warming are much more chaotic than simply an increase in "local"
temperatures. Consequently choosing an indicator species, such as numbers of
wintering Snow Buntings, (more buntings less heat and vice versa) may not be
appropriate.

Until the questions on what is limiting a species winter range can be
answered, ascribing changes in that range to climate change may be a bit
simplistic. For example shorebirds may be limited by seasonal cycles in food
or the number of days where it is likely to be cold enough to freeze their
feeding areas in estuaries. An increase in temperatures might lead to clearer
skies, more early morning frost, and as a result more difficulty in finding
food - driving the birds further south, not north. Or alternatively, windier
and wetter conditions, albeit warmer, might increase wind-chill and again
drive birds further south.

Speculation: On plan of attack might be to choose, generalist species, which
are able to find food across a broad range of habitats - for example the
beloved Starling. Assuming that food availablity is less of a problem for such
species then climatic conditions might be the limiting factor on either their
winter range, warmer equals wintering further north, or breeding success,
more food available earlier in the year = more broods and more young reared.

Life is never that simple, SIGH.


Stuart MacKay