When winter temperatures become really cold for an extended period of time in southeastern Pennsylvania, as elsewhere, impoundments, large and small, freeze over completely. Then a variety of wintering, waterbird species have no choice but to seek other sources of open water, including the slower-moving, but ice-free stretches of freshwater, inland creeks, streams and brooks. There those birds can still find food, and protection on the water, while making those waterways more interesting to us. In the farmland of Lancaster County, for example, wintering Canada geese, mallard ducks, black ducks, common merganser ducks, great blue herons, belted kingfishers, killdeer plovers and American pipits seek food in running water, and/or along its shores, or in the pastures and fields near the ice-free waterways when lakes and ponds are frozen and snow covers the ground.
One freezing, but sunny, day during February, 2015, I drove by a meadow of tall grass that has a slow-moving stream flowing through the middle of it about a half-mile south of New Holland. I saw a flock of Canada geese plucking and eating grass stems near the stream. And I saw a gathering of about 60 mallard ducks hunkered down in the grass to rest in the sunlight, but out of the cold wind, while a half dozen other mallards were swimming and feeding in the stream. Though I see both those species locally almost daily, those geese and ducks were striking in the warm sunlight and beige tall grass. And I was relatively sure those mallards were the same ones that regularly frequent a pond on the northern edge of New Holland. But they were forced to leave that pond when it froze and became attractive to ice skaters. As I admired the beauty of the scene, I thought it would be neat for a great blue heron to drop into the stream. A few moments later, one did! There it waded slowly, watching for fish it could catch and eat.
This winter, I've seen flocks of magnificent Canada geese on ice-free parts of the Conestoga River, and on creeks. They rest on the open water, and fly majestically and noisily out to pastures, rye fields and harvested corn fields to consume green blades of grass and rye and waste corn. When full, those stately geese power back to the waterway to rest, socialize and preen their feathers.
A few wintering black ducks rest here and there on waterways when lakes are frozen, but usually under the sheltering limbs of trees hanging over the water. Those dark ducks, then, are difficult to spot in such a niche. But being mallard relatives, the big, handsome black ducks often join mallards in corn fields in winter to shovel up waste corn kernels with their shovel-like beaks.
Common mergansers and belted kingfishers feed on small fish. But they turn to diving under water to catch fish in the still-flowing creeks when impoundments freeze over. Herons, mergansers and kingfishers all snare fish, but in different ways, which helps make them entertaining. These birds also catch fish at different depths, reducing competition among themselves. The herons wade on long legs and stretch out their long necks to get their prey. Mergansers slip deep under water from the surface, while kingfishers dive from a tree overhanging the water or from hovering into the wind to snare prey near the surface. All these bird species, however, catch prey with their bills.
A few each of Killdeer plovers and American pipits winter on the fields where they feed on invertebrates that are dead or alive when they find them. But when snow covers the fields, these birds join Wilson's snipe and song sparrows along the muddy edges of the waterways. The snipe and sparrows are along the streams all winter, regardless of the temperatures. The killdeer and pipits find innumerable invertebrates in the shallows and on the mud of the edges of the waterways and scrunch down among clumps of vegetation to avoid the cold wind.
Many of the above-mentioned birds will return to ponds and lakes when those impoundments thaw. But the flowing waterways were life-savers to many birds, when they were the only open water available to those birds.
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