[Taxacom] whooping crane migrations (was Taxacom Digest)

Kenneth Kinman kennethkinman at webtv.net
Sun Feb 5 16:38:34 CST 2012


Hi Gary, 
      I would agree that the whooping crane thing is based largely on
food.  If there is plenty to eat and the weather isn't too harsh, there
is no reason to waste energy and risk your life flying further south if
you don't have to.  Probably will see more of this as the populations
get bigger and the climate warms.  

      However, although a snowy owl irruption could be caused by a crash
in the lemming population, it seems more likely the result of plenty of
lemmings.  This results in a bumper crop of new owls, and the mature
owls (especially the larger females) easily drive out immatures from the
winter territories in Canada.  Even if there are plenty of lemmings,
territoriality will force owls south after a bumper crop of them is
produced.    

      Snowy owls are territorial in both the winter and the breeding
seasons, while whooping cranes tend to be territorial only during the
breeding season.  Snowy owls have fairly large territories and will
defend them even if there are enough lemmings to support more owls.  So
a crash in the lemming population isn't necessary for an owl irruption
to occur.    
           ---------Ken 

-------------------------------------------------------
Gary Anweiler wrote: 
Pretty different factors, but all based largely on feed. 
I believe the snowy's head south in numbers when the lemming cycles
dive...in others words, conditions in the far north; the cranes are
responding to conditions in the south.  Local conditions, but maybe
linked in a larger, more global or continental climate way? 
Gary Anweiler 






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