GELLERMAN: Caterpillars aren’t the only species with curious strategies for adapting to their surroundings. Here’s Michael Stein with this week’s BirdNote ®.

STEIN: Environmental conditions shape birds' bodies, even birds belonging to the same family. For example, consider the terns.

STEIN: The common terns you’re hearing have long, pointed bills they use to catch small fish. They migrate along both coasts and through the interior in spring and fall, on their way between nesting grounds in Canada and their winter home in the tropics. By migrating, they move from one warm and productive environment to another.

STEIN: Their close relative, arctic terns, look much alike, but both their bills and legs are shorter.

STEIN: Both species feed in exactly the same way, so why would the Arctic Tern’s bill and legs be shorter? Well, because arctic terns breed in the Arctic and winter in Antarctica.

STEIN: They’re subject to much more severe weather than are common terns. Because birds’ bills and legs are not covered by feathers, they lose heat. It just makes sense then for birds in cold climates to have short bills and legs – and less exposure to the cold.

GELLERMAN: That’s Michael Stein of BirdNote®. To see some photos of common and arctic terns, take a turn to our website loe.org.