During May in the northeastern United States, four kinds of common birds are obviously seen on and over extensive mud flats and shallow waters in rivers and larger impoundments. These interesting species, including bachelor groups of drake mallard ducks, flocks of Canada geese too young to pair off and breed, migrating least sandpipers and locally nesting tree swallows, help liven those seemingly barren habitats at that time. And each type of bird has its own foods while around those flats and shallows, which eliminates competition for those foods among them and allows them to live among the flats and shallows in peace and harmony.
Many mallard ducklings hatch by the end of April in this area. Their mothers are busy raising them with no help from drake mallards, which frees those males to form gatherings of their own on flats and shallows through much of summer. During that time the drakes "tip-up", with their tails in the air, to shovel up aquatic vegetation from the bottoms of shallow water.
Also in summer, mallard drakes molt their resplendent, "courtship" feathers, making them resemble the plainer, better camouflaged, hen mallards. Then the males grow new, handsome, courtship feathers that are mature by the end of September and adorn the drakes through the coming winter and spring.
Several full-sized, but sexually immature Canada geese gather into flocks on flats and shallows for safety and companionship. These large, majestic birds feed on tender grasses growing on the flats, and nearby, extensive lawns. And all the while they are gaining strength and wisdom so that in a few years many of them will pair off and rear goslings of their own.
Scores or hundreds of migrant least sandpipers stop their travels north to walk in loose flocks across mud flats and wade in inch-deep water to eat aquatic invertebrates they pull out of the mud before continuing their migrations north to raise young on the Arctic tundra of Canada and Alaska. They need lots of invertebrate fuel to make that long trip to the tundra.
Least sandpipers migrate north in May, after wintering on beaches and mud flats on Caribbean islands, Mexico's coasts and the shores of the southern United States. Being brown and darkly-streaked above and white below, these sparrow-sized sandpipers are hard to see on the flats and shallows until they fly or otherwise move. Sometimes flocks of least sandpipers, for seemingly no reason, suddenly sweep into the air and are off in wild, rocketing flight, quickly turning this way and that, showing white, then brown, then white again as they careen and circle, again and again, over water and flats. That rapid twisting of several birds in a flock at once in the air probably confuses hawks that would catch and eat sandpipers. Then, as suddenly as they took off, the sandpipers land again on the flats, looking like stones being tossed across the mud, and immediatly feed again on invertebrates in the mud.
By the end of May and into early June, most least sandpipers are on their way to the still-thawing tundra. But they were enjoyable to experience when they passed through this area in north-bound migration, stopping only to refuel.
While many mud flats and shallows are populated by gatherings of bachelor mallard drakes, immature Canada geese and feeding migrant sandpipers, loose collections of migrating and/or locally nesting tree swallows dash and swoop over the mud flats and shallows of rivers and lakes to catch flying insects. Those fast-flying, dodging swallows are entertaining in themselves to watch over bodies of water and flats where other kinds of birds are feeding.
Tree swallows are also handsomely dressed. Males are iridescent blue on top and white below. Their mates are more gray above. But both genders are beautifully streamlined for careening, maneuverable flight through the air after flying insects.
Mud flats are not as barren as they often look. They often have gatherings of a variety of birds, as well as a diversity of invertebrates, many of which ae food for those birds.
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