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Photo's
by Christine Kelly
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Did you know that
some shorebirds fly nonstop for thousands of miles? It's true. The
Red Knot (Calidris canutus), a medium sized sandpiper weighing in
at just 55 grams, travels up to 2,000 miles at a time between breeding
grounds and wintering grounds. |
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feats of migration have earned shorebirds
the nickname "hemispheric globetrotters". Amazingly, shorebirds
complete this trip on a diet of tiny worms and crustaceans! Before
starting the trip, a shorebird fuels up, increasing its body mass
by as much as 100%. During migration, a shorebird burns these fat
reserves and must replenish them at every stop along the way. These
rest areas are called "staging areas" or "stopover
sites". Such sites are typically highly productive wetlands rich
in invertebrates. Stopover sites are situated along historical routes
or "flyways". There are four main flyways in North America:
the Atlantic Flyway, the Mississippi Flyway, the Central Flyway and
the Pacific Flyway. Sometimes the important stopover sites along these
flyways are few in number and widely separated. Therefore, shorebirds
reliance on these geographic links makes them vulnerable to loss of
key staging areas. |
For example, Delaware Bay hosts between 400,000 and 1,000,000
shorebirds in May and June. Why do so many shorebirds stop here?
The birds have evolved migratory patterns that time their arrival
at Delaware Bay with the onset of horseshoe crab spawning. Horseshoe
crabs eggs are available in extremely high abundance, making Delaware
Bay a predictable stopover site for shorebirds.
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Why Do Shorebirds
Migrate?
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The answer depends on which perspective
you take. What does a shorebird call home- the arctic where it nests,
or the coastal areas of Central America, South America, or the southern
U.S. where it spends the winter? Shorebirds spend as much as 7 months
of the year on their over-wintering grounds. Why do they leave and
fly so far north to breed? The Canadian arctic, nesting grounds
for many species of shorebirds, offers rich resources that support
breeding adults and newly-fledged young. The land is so bountiful
from a shorebird's perspective, that it is more profitable to nest
there than in South America. Chicks are more likely to survive on
the plentiful resources in the Canadian arctic. But no sooner do
they arrive, than they have to turn around and fly south again before
severe weather starts. Shorebirds must leave their arctic nesting
grounds before food becomes locked up beneath ice and snow. Therefore,
nesting occurs over a brief window of time when the arctic tundra
has thawed enough for birds to obtain food. The price for increased
nesting success is a long, risky journey.
We should consider ourselves lucky that shorebirds' migratory routes
pass through many parts of the U.S. where we can witness flocks
of thousands coming and going on their long journey. Visit your
nearest National Wildlife Refuge during peak shorebird migration.
Depending on the location, fall migration often spans a wider period
of time, from late July until late October, while spring migration
lasts from early March in the south to mid June in the north. |
Visit Your National Wildlife
Refuge
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