On 24/01/2014 9:00 AM, Robin Dartington wrote:
> According to Wikipedia, a circadian rhythm developed in the earliest living cells as a way to avoid exposure to sunlight. Apparently all cells respond to a rhythm.  Apparently we need to ask a chronobiologist about longer rhythms. Anyone out there?

Most/many/all(?) these rhythms need to be regularly set.  Kept in 
continuous dark or light the day rhythm gets out of sync.    I am 
nursemaid to a blind nocturnal sugar glider at the moment.  Its activity 
cycles gradually shift to be 12 hours out.   Humans do the same.  This 
deepens the mystery of bees kept in conditions whereby it seems they 
would have difficulty in measuring day length , or indeed whether it is 
day or night.


> Presumably annual rhythms underlie annual migrations of some birds and mammals and fish. And leaf bud and leaf fall.  These can be marginally adjusted to match conditions in any one year but seem a powerful force as migrations do occur annually around the same time.  As does the turning off and turning back on of bee brood rearing.

As we have said,  bees in Oz may, if the floral conditions are 
conducive, have brood all year, in fact it is the norm at my place. 
Wanderer butterflies do not migrate here.  Whatever the trigger in North 
America, is does not function here.  Day length changes are commonly a 
trigger, but are often over ridden or modified by other factors.   We 
are already seeing some changes which may be due to global warming.  
Coucals, a bird that used to move north for the winter, now stays put in 
this area now.  Whereas my hybrid willows seem to be stuck to bud burst 
almost to the hour.

Geoff Manning

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