Fall means migration to many species of birds, and beachgoers and birders alike enjoy watching shorebirds. From tall, leggy waders to stocky little plovers, shorebirds follow the tides as they rest and feed, breaking the long trip on our beaches. one of the most common september sights is the semipalmated Plover.
Semipalmated Plovers nest in the far north, from the north slope of Alaska to the shores of Hudson and James bays, to Newfoundland. They can be seen across the entire United States on migration, but many head for the coasts. They spend winters along saltwater coastlines on both sides of the continents of North and South America. In the west they winter from California to Chile. On the Atlantic side they range from Virginia to Argentina. They migrate in stages, with females leaving first, followed by the males, and then by the birds of the year. These can be distinguished by fresher, more scallop-patterned plumage.
Semipalmated means partially “palmate,” or slightly palm-like. There is a small bit of tissue, or webbing, between their front toes. Their feet are not fully webbed like ducks or gulls, but their digits are not completely separated. They are not swimmers by preference, but they are nonetheless comfortable in damp places.
Like all plovers they have a characteristic style of movement, which is to run-stop-look, run-stop-look, run-stop-peck, as they feed along the shore. They are often seen on beaches with Sanderlings. But Sanderlings follow the waves, dashing up and down like little wind-up toys as they follow the edge of the surf.
They are active between the waves’ advance and retreat. Sanderlings hang together, feeding in close groups. Sanderlings are slimmer. Plovers are plump and more dignified. Semipals usually spread out more and work higher on the berm of the beach. They concentrate in flocks to sleep, where a few vigilant birds maintain the predator watch. Unlike Sanderlings, they have yellow legs and feet, short bills and a white collar around the neck defined by a dark ring of brown or black plumage.
They are sometimes mistaken for the much rarer – and much more invisible – Piping Plovers. When the species sometimes overlap, the differences are more obvious.
The quickest way to differentiate them is by color. Piping Plovers are the color of dry sand, practically invisible on a white, sandy beach. On the contrasting background of a damp mudflat they look almost white. Semipals are the color of wet sand or mud. They tend to blend in well in damp, marshy spots and stand out on more dazzling, dry shores. They are much more numerous, so it is a lot easier to see them and enjoy their antics.
Like all shorebirds, they were hunted relentlessly in the market -gunning era of the 19th century. Along with most other winged creatures, they suffered increasingly with advances in transportation and firearm technology. In the 1920s state ornithologist Edward Howe Forbush, part of whose job was to determine useful versus harmful species, lamented, “This Plover is so small as to be of little value as game but as it is of some service as a destroyer of noxious insects it should be perpetually protected as a part of the interesting life of our summer beaches.”
Protection arrived in 1918, in the form of an international treaty protecting migratory birds.
In the 1940s, Edith Andrews wrote, “Fifty is the maximum ever seen in a day on Nantucket, in striking contrast to the thousands that flood down the shoreline of the outer Cape.”
In the last decades numbers on the Cape have diminished, and are recorded more in the hundreds, rarely topping even 1,000. But on Nantucket these days, sight records occasionally top 100. So, their situation here has apparently improved and our beaches must be counted as important to them.
We have to wonder: why have they done so much better than the Piping Plovers? Several factors probably apply. Their breeding grounds are mostly far from concentrated numbers of humans.
This means that their life cycle is less interrupted by human development. Their wintering territory is vast and strung out. They eat a wide variety of foods, from fly larvae to polychaete and nerieus worms, to the tiny shrimp-like crustaceans that live within sandbars and saltmarshes. They consume flies, beetles, even spiders. They will eat small mollusks or even seeds. They can feed by day or night, following the tide or ignoring it as supplies dictate. But their lives are still precarious.
Semipalmated Plovers have some natural predators such as ravens, as well as hawks and falcons. They compete for food and territory. An adult’s life span is only five or six years, on average. They don’t breed until the second or third year, or even necessarily every year. They only produce one brood per year.
In the more accessible of their northern breeding grounds, where they nest on raw gravel, they are vulnerable to mining interests. An excavator can eliminate a whole breeding season for a short-lived bird. They have also shown detectable levels of pesticides such as DDT and DDE, as well as pollutants such as PCBs, mercury and selenium.
These are a concern because they are retained in fatty tissues. Forbush commented that Semipalmated Plover were “exceedingly fat in the autumn and I have known the fat of the breast to split open when the bird struck the ground after being shot when flying at height. The fat is not only everywhere under the skin but it envelopes even the viscera . . . How birds under these circumstances are able to fly so vigorously on their long migrations, or even to fly at all is certainly a mystery.”
Science has since illuminated some of the mystery: fat is the shorebirds’ fuel for those very migrations. It’s not just the flying. Along the way they also have to evade predators, forage for food and dodge bad weather or adverse winds. Unlike those of us who turn protein and carbohydrates into energy for our bodies, migrating birds make fat into their jet fuel, burning it to enable them to do the vigorous exercise of their marathon journeys from North to South America.
But this in its turn has opened up yet another mystery. How do birds cope with the byproducts of fat combustion, the free radicals and oxidative compounds that can damage cell tissue? This is a question that engages some current researchers working in molecular biochemistry.
While some songbirds appear to address the problem of oxidation damage through diet, con-
suming anti-oxidant-rich berries, others seem to have enzymes or other compounds in their cells which cope with the oxygen-reactive compounds. We don’t yet know how birds achieve the peak functioning needed to “exercise” their way over thousands of miles despite the use of fat.
Scientists will continue to tease out new discoveries. Some may turn out to be of tremendous benefit to humans. But in the meanwhile, any-
one can enjoy watching these creatures who share our world, knowing there is still some mystery to be explored, some unexpected marvel. For birdwatchers, there’s no pal like a Semipal. ///
Virginia Andrews writes the weekly “Island Bird Sightings” column for The Inquirer and Mirror, Nantucket’s newspaper since 1821, and is a regular contributor to Nantucket Today.
