Biology Reference
In-Depth Information
states may take advantage of warm temperatures and earlier food availability to migrate
andbreedearlier.Meanwhile,birdswinteringinthetropicshavenowayofknowingwhat
the weather is like across the Gulf of Mexico, and arrive closer to their normal arrival
date, sometimes missing important surges in insect numbers that fuel their migration and
provide a good abundance of food for breeding.
Finally, the northern range limits of some opportunistic birds are related to temperat-
ure. When there is less ice in winter, Mallards and Canada Geese winter farther north,
and their winter range may expand. More and more starlings, robins, and other abundant
species may survive in higher numbers in northern winters, in some cases crowding out
birdsthataremoreadaptedtoharshconditions;asthosepopulationsretreatfurthernorth,
their potential total range will shrink. Melting permafrost is expected to affect lemmings,
the primary food for Snowy Owls. Many species of birds are physiologically stressed by
extreme heat, too; increasingly hot summers may take a heavy toll on these species.
Q I keep hearing about birds in decline, but I'm seeing more robins than ever.
What's the truth?
A
You're right that robins are increasing. These
generalists
have adapted very well to
the habitat changes that come with urbanization, and they are thriving. But some birds
are dangerously declining. In 2007, the National Audubon Society released a report that
showed many of our most common and beloved birds have declined by 50 percent or
more since 1967. For example, Eastern Meadowlarks have declined by 72 percent.
The population density and range of Greater Sage-Grouse have shrunk since Lewis
and Clark documented them on their expedition. Common Nighthawks and Whip-poor-
wills grow increasingly scarce. The Red Knot declined by fully 80 percent between 1995
and 2005, so in 2005, environmental organizations petitioned the U.S. Fish and Wildlife
Service (USFWS) to list the
rufa
subspecies as Endangered and to designate critical hab-
itat for them, but their petition was denied. It grows increasingly difficult to “list” declin-
ing species to give them the protection that official designation as a Threatened or En-
dangered species affords.
