Roost preference

evoluhol at evoluhol at
Wed Sep 23 07:16:45 EDT 1998

As there are studies of the monarchs done by college students at St. Louis
Obispo near the Pismo Beach colony in California, they may have some
documented information on the answer to this.  There the overwintering
colony is always in the same small grove, primarily eucalyptus and
conifers at the edge of huge costal sand dunes.

Personally examining colonies in Mexico and over a dozen colonies up and
down the coast of California, I noted that when sleeping (does not apply
when sunning) overwintering colonies and clusters almost without exception
chose pines in Mexico or eucalyptus in California no matter what other
kinds of trees were around.  As eucalyptus is totally alien to California
yet clearly is the roosting tree of choice there must be an
overwhelmilngly strong attractant.  Evolution would say that it somehow
fits their survival.  Is it because of the intense aroma and toxic oils in
the eucalyptus?  I might add that migrating overnight gatherings here in
New York State show no preference for overnight roosts -- all it takes is
one male to settle down and release pheromones and others come and the
group size increases -- maple, privit, whatever.  Incidentally this week
they are moving south in quite large numbers across southern New York.

Micro climate other than aromatic toxicity would have little effect on
monarchs as the clusters at rest in the pines in Mexico or the eucalyptus
in California are always out on the ends of branches in full view/sun/air

Dave Bouton

> Is there some reason other than 'nothing else available' that would make 
> Eucalypts attractive for Monarch roosts.  Are they taller (less 
> accessible), different branch structure (easier roosting), repellent of 
> predators, etc???
> Mike Gochfeld

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