Geoff,
I agree with you to your last comment - migrants are affected mainly by weather but not easily to be found with climate change.
Migrants might not be the best study object of this topic. When I have some preliminary analysis of the waterbird count data, some birds seem react to climate change. For example: Intermediate Egret, Chinese Spot-bill Duck (and prossibly Mallard too), probably wintering Great Knots and Whimbrels might have increase or decrease of their numbers in order to the change of temperature of winter months.
Tung
