Gulls Wintering on Impoundments

     Many times in winter over the years, I have visited the several large, human-made impoundments in southeastern Pennsylvania to experience Canada geese, snow geese, tundra swans, a variety of ducks, great blue herons, bald eagles and ring-billed gulls that regularly winter on them, but not all at once and not on every lake.  These are birds that traditionally wintered on the Susquehanna and Delaware Rivers and Chesapeake and Delaware Bays, but have adapted to built impoundments. 
     I visited Blue Marsh Lake, a huge impoundment in Berks County, one recent mid-afternoon to see if masses of ring-billed gulls were still spending winter nights there, as they have for several years.  They were, by the thousands.  Ring-bills are the main wintering bird species on that built lake, resting on its water, or ice, every winter night, as other ring-bills do on many other impoundments.
     Ring-billed gulls have long adapted to wintering on local inland habitats, including harvested fields, parking lots and, most recently, landfills, to get food, and on built lakes to rest in relative peace.  They have been a common, wintering species here for many years, bringing a touch of rivers, estuaries and sea coasts inland.   
     During winter days, thousands of ring-bills concentrate at feeding sites, especially landfills.  Most gull species are preadapted to scavenging in open habitats and, therefore, can make good use of landfills.  But by mid-afternoon, long lines and flocks of ring-bills wing swiftly across the sky, flock after flock, as if on an aerial highway, to return to their chosen lake, including the one at Blue Marsh, for example, to spend the night in relative safety in a familiar habitat.  Each gull flaps powerfully and soars gracefully over the lake and eventually sweeps down to land on it, or a gravelly beach on its shore.  And all those gulls together create quite an inspiring show of beauty and grace as they land on Blue Marsh Lake and beach, as on other impoundments.
     The presence of the many adaptable ring-bills on built lakes may attract other, more common, species of wintering gulls to rest on those inland impoundments, including herring, great black-backed and, maybe most recently, lesser black-backed gulls.  These three kinds of gulls, plus an occasional glaucous or Iceland gull, are also adapting to wintering on inland impoundments to some extent, and feeding at landfills.  Herring gulls look like larger editions of ring-bills.  Great black-backs are white with black upper wings and backs and pink legs.  And the smaller lesser black-backs are white with dark-gray upper wings and backs and yellow legs.
     Human-made impoundments and landfills have changed the wintering habits of the more adaptable and common kinds of gulls in southeastern Pennsylvania, and North America in general, to the birds' benefit.  And those gulls help bring beauty, grace and excitement to those built habitats in winter.