Biology Reference
In-Depth Information
they wander more loosely in search of their winter diet of fruits and berries, which are
unpredictably abundant in some places and sparse in others.
Those robins that remain in the far north tend to be males who get the advantage of
arriving first and claiming the best territories in spring, if they survive the winter. They
will move on if they deplete the food supplies, and some succumb to bad weather and
starvation. So the genes for longer distance migration remain alive in the population, too.
Major spring migratory movements of robins follow the thaw pattern when earthworms
first appear, about where temperatures are starting to average 37°F (3°C). But in many
northernareas, wintering robinsarearoundlongbeforethe“first robinofspring”arrives.
How do you tell that first robin of spring from the last robin of winter? If they're
feeding in flocks in fruit trees, they're still exhibiting winter behaviors. When they run
on lawns feeding on worms and start singing, they're showing spring behaviors; usually
spring robins are seen as individuals, pairs, or fighting rivals. In the changeable condi-
tions of early spring, a robin may exhibit spring behaviors one day and revert to winter
behaviors when a late blizzard blows in.
