Asked Questions about Robins: Spring Migration
Why do females arrive later than males?
A. Male and female robins both feed their babies. But before the
eggs hatch, the male and female have different jobs. The female builds
the nest, and produces and incubates the eggs. The male chooses and defends
their territory, and finds some nest materials for the female to use.
He must return early to have a good choice of territories and to protect
his choice against robins migrating through. If snow or ice storms limit
his food supplies for a few days, he can still easily survive until the
next thaw. The female, has no urgent need to return early, since there
is nothing important for her to do until there is a good mud supply for
building her nest. As a matter of fact, if she builds too early, hard
frosts at night can weaken her nest. And if she runs out of food so soon
before the nesting season, it can make it hard for her body to produce
eggs. So she waits until conditions are more favorable so she can continue
to get a reliable winter diet as long as necessary.
Q. How do I tell the first robin of spring
from the last robin of winter?
A. There is no one single moment when a robin changes from a wintering
bird to a migrant. Winter and migratory behaviors include
- Feeding in flocks
- Eating fruit
- Flying in flocks
- Getting along peacefully
Spring behaviors include
- Running on lawns
- Eating worms
- Territorial battles
- Carrying nesting materials
is, one day an individual robin may be eating worms and singing, but if
a sudden ice storm or other bad weather reappears (which happens a lot
in early spring!) that robin may again join a feeding flock and act like
a winter or migrating bird for a few more days.
So deciding whether a robin is a winter bird or a spring bird is a subjective judgment. We at Journey North consider
a singing robin to be a spring bird, though we realize that sometimes surging hormones make robins sing even in
winter flocks. In the majority of cases, robins really do wait to sing until they have reached their territory.
Also, some singing birds in the vicinity of winter flocks are actually individuals that are not part of the flock,
but have already claimed their territories. We've noticed that after the first robin arrives in some Minnesota
backyards and starts singing, large flocks of robins will still be passing through for several weeks. Local birds
sometimes seem to sing more often while these flocks are present in the area, as if to warn them that some territories
are already taken.