A common tern (Photo: Amanda Boyd, USFWS)
Arctic Tern vocalizing (Photo: Kirk Rogers USFWS)
Arctic Terns have evolved to have shorter bills and legs than their relative the Common tern. Michael Stein explains why.
[BIRDNOTE® THEME]
GELLERMAN: Caterpillars aren’t the only species with curious strategies for adapting to their surroundings. Here’s Michael Stein with this week’s BirdNote ®.
[TERN CALLS, WATER SOUNDS]
A common tern (Photo: Amanda Boyd, USFWS)
STEIN: Environmental conditions shape birds' bodies, even birds belonging to the same family. For example, consider the terns.
[COMMON TERN CALLS]
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.
[COMMON TERN CALLS]
An Artic tern sits on a nest. (Photo: Tim Bowman, USFWS)
STEIN: Their close relative, arctic terns, look much alike, but both their bills and legs are shorter.
[ARCTIC TERN CALLS]
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.
[ARCTIC TERN CALLS]
A common tern (Photo: USFWS)
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.
[CALLS OF TERNS]
GELLERMAN: That’s Michael Stein of BirdNote®. To see some photos of common and arctic terns, take a turn to our website loe.org.
Links http://www.birds.cornell.edu/Page.aspx?pid=1478&ac=ac - Bird audio provided by The Macaulay Library of Natural Sounds at the Cornell Lab of Ornithology, Ithaca, New York. Common Tern recorded by C.A. Sutherland and R.S. Little. Arctic Tern recorded by G.A. Keller. Ambient waves recorded by J. Kessler, Kessler Productions http://www.birdnote.org/birdnote.cfm?id=1015 - BirdNote® Why Arctic Terns Have Short Beaks was written by Dennis Paulson