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Sanderlings pass through our area twice a year during their long-distance migration. This adult is on its way to southern South America for the winter. Keith Corliss

Flight Lines: Shorebird stories are almost mythical

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It actually began some weeks ago, the arrival of the first migrant shorebirds into our area following the breeding season.

An individual here, a small group there, and large concentra-tions at ideal sites. To think that most of these skinny-legged birds probing around in the shallow mudflats will within weeks be seeking invertebrates to eat in similar habitats a hemisphere away never ceases to astound.

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There are in the neighborhood of 30 expected shorebird species that pass through North Dakota during the typical calendar year; less than a third stay within our border to nest.

The remaining birds – over 20 million individuals –steadfastly steer well north, seeking the productivity of the short but robust tundra summer.

Unlike spring when the siren song of procreation brings an almost frantic urge to shorebird movements, fall migration is a more drawn-out leisurely affair. (Note: Birders typically refer to these seasonal patterns as “spring” and “fall.” These are loose terms relative to the breeding season and not necessarily indicative of the calendar.)

By perhaps late June, the first “fall” shorebirds appear. These are usually adults that failed to nest for one reason or another. Following sometime later will be adult nesting birds. Later still will be the young of the year, with their sharply defined crisp new feathers.

Overlap occurs throughout the weeks, so that by this time of year a mélange of adults and juveniles with varying plumages populate feeding areas.

While we might be able to watch shorebird numbers in the hundreds or perhaps thousands if we are very lucky, these pale in comparison to some of the more important stopover sites such as Delaware Bay, Cheyenne Bottoms in Kansas, or Washington’s Gray’s Harbor, for instance.

It is estimated that more than 80 percent of the entire North American population of some species will appear at one of these grounds, known for their superabundant food resources.

It is understood that virtually the entire world populations of Western Sandpipers and Dunlins stop at the Copper River Delta in Alaska, where they will refuel on a diet almost exclusively made up of tiny clams in spring. Over 1 million shorebirds have been recorded in a single day here, illustrating just how vitally important the quality and integrity of these locations are.

What makes these sites so critical is the fact that most shorebirds undergo an astoundingly long distance migration and require huge fat reserves in order to survive the ordeal. For instance, it wasn’t until recently that science discovered Bar-tailed Godwits make the trek from their Alaskan breeding grounds to a wintering site in New Zealand in one flight, some 6,500 miles.

Perhaps more familiar to us is the Sanderling, a commonly encountered spring and fall visitor locally. It might surprise some to learn it boasts the longest migration of any shorebird, flying in stages from nesting sites as far north as central Siberia to the southern tip of South America and back every year.

Again, almost beyond amazing.

I hope to one day witness the spring migration at Delaware Bay where oodles of shorebirds time their arrival to coincide with the abundance of horseshoe crab eggs. Untold millions of these calorie-rich morsels become available to the birds during the short period of crab spawning. Someone much smarter than me figured out that Sanderlings must eat an egg every five seconds for 14 hours a day in order to rest and regain the weight necessary for it to successfully complete its spring journey.

There aren’t nearly enough superlatives to describe just how fascinating some of the shorebird life histories are. In some instances it seems as if a more marvelous tale couldn’t be told by making it up.

There is still much to know about migration in general, that of shorebirds in particular. It’s somewhat ironic that we can see a thousand birds at a particular stopover site and not be entirely sure where some of the birds go from there. Overnight some mysterious unseen signal is received and the birds are gone, not to be seen again until spring.

It’s a knotty baffling portrait slowly being painted with the aid of science and technology. In the meantime, we can continue to provide useful pieces of this puzzle with our detailed reports of species and numbers from our favorite shorebird watching sites.

Corliss is a West Fargo resident, avid birder, and ND Game and Fish volunteer instructor. He serves as a corporate pilot for Forum Communications. kcorliss@forumcomm.com.

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