It’s all about food. Birds perform marvelous feats: migrating from one pole to the other, raising multiple clutches of young in a single season, tolerating winter temperatures as low as 70 below zero.
But each of these astounding activities comes with a big ‘if.’ If the birds can find enough food.
Birds can be surprisingly resourceful in finding food. I saw an unusual feeding behavior on a gusty day in Lubec just last week. Mountain ash had a productive growing season and the bright red berries were conspicuous and abundant.
The mountain ash that I was watching were small, no more than 10 feet tall, right along the shores of Cobscook Bay. Suddenly I saw several herring gulls doing their best hummingbird impression. The gulls were having a snack by facing into the wind, hovering over clusters of mountain ash berries and nimbly plucking berries with their bill. I think the mountain ash were too small to support the gulls if they had tried to perch on a branch. I had to tip my hat to the gulls for this foraging behavior.
Herring gulls have a broad diet. Along the coast they will take mussels, clams, crabs or sea urchins. Insects, frogs and fish form part of the diet. They flock to recently plowed fields for displaced earthworms. Eggs of other birds and even smaller birds can be taken.
And of course we know they are fond of french fries and other human-generated food. A visit to an open dump like the Hatch Hill Transfer Station in Augusta can yield over a thousand herring gulls, following the bulldozer that moves the trash around. Carrion, rodents and discarded food are all on the menu.
Herring gulls have benefited from human alterations to the landscape. Checking Ora Knight’s 1908 book, “The Birds of Maine,” we find that herring gulls were not common birds at the turn of the 20th century in the southern two-thirds of the state. Knight lists them as rare in Kennebec County, a regular visitor throughout the year in Waldo County, a few in summer in Sagadahoc County and locally common in Hancock County.
While in Lubec, my wife and I had the good fortune to see a cattle egret consorting with a small flock of sheep on the western side of town. The egret had been found a day earlier by Richard Garrigus.
Cattle egrets make a living by consorting with ungulates. The egrets feed on the insects that are impelled to move as a cow or sheep grazes in a meadow.
But cattle egrets are not native to North America. Their original range is in the Old World, where the birds would more appropriately be named wildebeest egret or zebra egret.
We have a number of bird species that were introduced by humans into North America. The rock pigeon, European starling and house sparrow are the most successful introductions, although I use successful in a guarded sense because starlings and house sparrows have had deleterious effects on many of our native cavity-nesting birds.
The cattle egret is a different story. These birds introduced themselves to the Western hemisphere. The first colonists crossed the Atlantic from Africa in 1877, arriving in Suriname in South America. Cow farms were perfect substitutes for African savannas for the egrets. They spread through the Caribbean Islands, arriving in the United States in 1941. The first nesting record in the U.S. was in 1953. They nest broadly throughout the southeastern U.S. with breeding outposts as far north as New York, North Dakota and Ontario.
Cattle egrets do have a wanderlust, often dispersing long distances in the fall. Despite their relatively limited nesting range in our country, cattle egrets have been documented in all of the lower 48 states, Alaska and the southern portions of most Canadian provinces.
Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at: firstname.lastname@example.org
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