Jetties of boulders, fishing dock pilings and stone sea walls are recent, human-made habitats along the shores of oceans, including the North Atlantic of North America. These structures are like rocky, ocean shorelines in that aquatic vegetation, (seaweed of various kinds) multitudes of blue mussels and other sea invertebrates live on them where ocean breakers regularly crash and splash. Jetties, extending up to a few hundred yards into the ocean, were built to retain sand on public, recreational beaches. New Jersey has several rock jetties that protect its money-making beaches.
Masses of blue mussels cling on to and colonize the hard surfaces of pilings, seawalls and jetties. Those dark-shelled, oblong members of the mollusk family are packed tight on the boulders. And those mussels are an important food source, either directly or indirectly, for several kinds of handsome, wintering waterfowl and shorebirds.
At least nine kinds of sea ducks, all of them attractive in appearance, consume blue mussels on jetties, including long-tailed and harlequin ducks, two types of eider ducks, three species of scoters, greater scaups and American goldeneyes. All these species raise young in northern Canada and Alaska, but winter along sea coasts. And they all ingest blue mussels from jetties at some time or another in winter. A field guide to North American birds will illustrate how beautiful these duck species are and where they rear offspring.
Long-tailed ducks are so-named because each handsome drake has a couple of long tail feathers. Small groups of long-tails fly swiftly in low, picturesque lines where breakers rise from the ocean, fall over with a crash and sweep up the beaches. The strong-swimming long-tails dive under water from the surface to tear mussels off the wave-battered jetties with their tough beaks, backed by powerful muscles.
Harlequin ducks nest along swiftly-flowing streams in Canada. Both adults and ducklings swim and walk along the bottom of those waterways to eat a variety of invertebrates. This attractive species probably is the most typical one along rock jetties. Harlequins, too, dive under water to rip mussels from the water-washed boulders.
Elegant common eider ducks and king eiders occasionally feed on blue mussels on jetties, but not as regularly as long-tails and harlequins. These two species generally winter farther out in the oceans where they dive for mollusks and crustaceans.
The three, closely-related scoter species are mostly black, with other colors that identify them. Black scoters usually winter along breakers and jetties and dive for mussels, but their close relatives, the surf and white-winged scoters, generally spend winters where estuaries flow slowly into oceans. However, surf and white-wings will also ingest blue mussels off jetties at times by diving under water after them.
Greater scaups are members of the bay duck family. But certain individuals of this species also dive under water to feed on blue mussels on jetties, adding more diversity to this group of mussel-eating sea ducks.
Many American goldeneye ducks winter on the Susquehanna River and other rivers. But some of them winter near the shores of inlets and bays, and the ocean, where they dive for aquatic crustaaceans, mollusks and insects on the bottoms of large waters. Therefore, some goldeneyes dive for mussels on jetties. This species is often called "whistling ducks" because its wings whistle loudly when the birds are in flight.
Brant are a species of attractive, small goose that feed, in little groups, on plants along the shores of bays, inlets and oceans during winter. Some individuals of this interesting species, while floating, bobbing and swimming in the wave-tossed water beside jetties, sometimes feed on the vegetation growing on those ocean-washed lines of human-placed boulders jutting into the ocean breakers. Brant, by the way, are most attractive when flying in small groups low over bodies of salt and brackish water close to shorelines.
Purple sandpipers and ruddy turnstones are species of dark shorebirds that regularly winter on rock jetties, the sandpipers exclusively so. There individuals and little groups of these species feed on small, aquatic invertebrates that shelter among the mussels and vegetation. The dark feathering of these bird species camouflage them among the rocks, which helps conceal them from the good vision of peregrine falcons wandering along the seacoast.
Though devout beachcombers for edible tidbits washed onto the beaches by ocean waves, some sanderlings, which are a light-gray and white kind of sandpiper, feed on invertebrates among the mussels and seaweed on jetties. Sanderlings might give purple sandpipers and turnstones a bit of competition for invertebrates on jetties, but the former species isn't often on jetties.
Occasionally a few American oystercatchers eat some blue mussels on jetties. This is a pigeon-sized bird on stilts. This handsome species is black on top, white below and has a long, thin, blood-red beak. They use their bills to pry open mollusk shells to eat the body inside.
Rock jetties are intriguing, human-made habitats that benefit several kinds of feeding birds in winter. Some species consume the mussels, brant ingest aquatic plants and shorebirds eat small invertebrates sheltering among the mussels and vegetation. And we can experience some of these birds, if we are along jetties in winter.
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