James C. Leupold - USFWS
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Discussion of Challenge Question #9
"Do male robins mate with more than one female during the nesting period? What evidence do you have support
Most evidence from bird banding studies indicates that paired robins stay mated through a spring/summer season,
especially if their nests are successful. However, if they lose their eggs or babies, they sometimes leave the
territory, and at that point may separate. When the female lays a second set of eggs, the male takes charge of
finishing raising the first brood of babies, so they have a better chance of raising more babies by cooperating
and staying together.
Most ornithologists assume that a pair of robins won't mate with other robins during the season. This is probably
usually true, but ornithologists are discovering that individuals of many species of birds actually do sometimes
mate briefly with birds that aren't their actual mates, and this may sometimes be true of some robins.
Although both males and females usually return to the same area each year, banding studies do indicate that it's
not unusual for them to choose a different mate from one year to the next.
The only way people could be ABSOLUTELY CERTAIN that a pair of robins remained together over the season would be
to mark the birds somehow, using leg bands or dabbing some colored non-toxic paint or dye on some feathers--this
will only last until the birds molt, usually in July. However, these techniques are only allowed by licensed
banders, and so normally people can't use the method for studying their backyard birds.
But if you pay close attention to your birds, you may find some unusual characteristic--a small discolored area
of feathers, a feather growing incorrectly, or a minor deformity--that helps you recognize a particular individual.
And the only way that anyone can be certain that no other males mated with a particular female is to take blood
samples of her babies and determine for certain that they all have the same father.
One of the most fascinating aspects of ornithology is that so much is really not known or understood, even today,
about common birds. The more you pay attention to your backyard robins, the more you may discover that no one
has figured out before!