Subject: Re. Robins
Date: Nov 06 13:48:21 1995
From: Jack Bowling - jcbowling at mindlink.bc.ca


Jim Rosso asked -

>I am very interested in "sex-segreated migration". <cut> Why would
>sexes of the same species migrate in different ways? How would that
>have evolved? What would be the advantages of doing this? I can sort of
>understand why adults might migrate earlier than juvenilles. There are
>strategies that make some sense. (Of course I recognize the whole
>anthropomorphic realm of sense) But differences between the sexes in
>matters of migration is most intriguing.

It is quite common among passerines. Famous examples from our
part of the world include Yellow-rumped Warbler and Red-winged Blackbird
in which males arrive up to two weeks ahead of the females in the
spring. Easy answer for this would be it gives the males time to vie for
territories before the females arrive so all the female does is pick the
best male and go from there. Autumn migration is another thing, though.
There is ample evidence that several owl species have sex-segregated
migrations e.g. Boreal Owls in which the males move farther south than
the females. Also, females tend to be more faithful to natal grounds
than males.

- Jack




Jack Bowling
Prince George, BC
CANADA
jcbowling at mindlink.bc.ca