birdsoup

Although autumn officially begins this week, birds don’t check the calendar to decide when to start their southbound fall migration.  Shorebirds are early birds beginning in late-July/August.  Most songbirds begin in September.  Birds are still headed south in October.

Why do birds migrate?  It isn’t because they don’t like winter weather.  The can tolerate cold temperatures.  Scientists believe they migrate for food.  And not all species migrate. 

As an over simplification, backyard birds fall into two major categories:  those that eat seeds and those that eat insects, bugs, worm, etc.  Seed-eating birds generally do not migrate.  They can find seed all year, even on the coldest winter days.  Insect-eating birds, however, do migrate.  Since insects and bugs do not survive cold temperatures, the birds can’t find food in winter.  So they head south to warmer climates where insects are still abundant. 

Look at the perky Robin running around on your lawn looking for worms.  Now imagine your lawn covered with 3” of fresh snow.  How many worms would the Robin find then?  That’s why they head south.  At least most of them do.

Nothing is absolute in nature.  So there are always some Robins around in winter.  Hundreds were seen on last year’s Christmas Birds Count for Westchester.  (Doug Bloom jokes that they are Canadian Robins who fly south to Westchester.  )  How do they find worms in the middle of winter?  They don’t.  Instead they switch their diet to eating berries.  They also change other behavior.  In summer, Robins are loners.  They don’t hang out with other Robins.  In winter, however, they form small flocks and roam the area searching for berries.

A teacher once told me about a tree on the school grounds that was packed with berries.  One snowy winter day a flock of Robins show up.  They quickly devoured all the berries in the bottom third of the tree.  On the next day they ate the middle berries.  On the third day that ate the berries at the top.  When all the berries were gone, they left.

See how many Robins you see this winter.