>  These results coincide fairly closely with
>Wedmore's idea of a period of quiescence followed by brood-rearing
>as soon as colder conditions set in;


I read years ago that temperature was the trigger for winter brood 
rearing. As the temperature decreases, the cluster tightens. As the 
cluster tightens, the core temperature of the cluster increases. When 
the core temperature reaches 95 F or so, brood rearing starts.

I can't remember where I read it, and don't know if it is so.
Mike

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