Winter Riparian Birds along the Front Range

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by Scott Severs, Wildlife Biologist, Walsh Environmental

After an extended warm fall and early winter, colder weather has finally settled in, and so have the winter bird species that utilize lowland riparian ecosystems along the Front Range of Colorado. Gone are the songbirds of summer that left as the leaves fell from the trees and the bounty of insects associated with them. Some bird species have adapted to stay year-round, and others have arrived from further north to take advantage of milder conditions from which they left. While our landscapes can appear stark, these seemingly empty woods are full of life as the value of riparian woodlands and waterways continues into the cold season. A multitude of waterfowl, songbird and raptor species to observe make visiting a riparian ecosystem a worthwhile winter activity on a great many of the Front Range greenways interspersed throughout our towns and cities.

Intermittent open pools of water interspersed with frozen sheets of ice often host several species of waterfowl that have escaped frozen lakes and ponds from the high country and beyond. Along with the archetypical mallards, other surface-feeding or “puddle” ducks have joined them. Among others these include gadwall, American wigeon, northern shoveler, and wood duck, each adapted to take advantage of invertebrates, aquatic plants, and algae drifting in the stream water. Other species of waterfowl, the divers, also search for holes in the ice, using their ability to submerge to chase fish or harvest mollusks and invertebrates from the stream bottoms. Diving ducks often observed this time of year include common goldeneye, redhead, and common merganser. All these ducks are joined by their larger cousins, Canada and Cackling Geese, which use longer necks to reach food items the surface ducks cannot. Two fishing experts, the belted kingfisher and great blue heron, hangout bank-side waiting patiently to take advantage of any unsuspecting trout or minnow.

While the large size of waterfowl makes them relatively easy to observe, finding winter songbirds along riparian corridors can be tricky. Songbirds have undergone a fundamental switch from strongly territorial nesting pairs, to flocks of family groups and mixed species. The primary components of the flocks are black-capped chickadees, joined by mountain chickadees, white-breasted nuthatches and brown creepers and others, many moving down-slope from the coniferous forests. These restless flocks are constantly on the move; one moment the woods can be silent, and next a group can fly in frantically searching for hiding insects or leftover seeds from the summer bloom. Chickadees and nuthatches share the ability to cache food for the winter, hiding items for later eating in the furrowed bark of willows and cottonwoods. Not long after the first precipitation falls, the diversely patterned juncos appear along the corridor, consuming plant seeds under the cover of trees and shrubs. Many people fondly call them the snowbirds, reflecting on their arrival with the first snow. As it turns out, chickadees are good to associate with as they act like sentinels, warning all with high pitched alarm calls should a predator appear.

The winter flocks must remain on the move to stay one step ahead of the raptors that are following close behind to capture any unsuspecting songbird prey. Resident year-round in riparian zones adjacent to pastures and meadows are American kestrels, our smallest falcon, waiting patiently at the tops of trees usually watching for mice or voles, but occasionally taking a bird. Even more specialized to capture birds are the forest-dwelling accipters, also known as the sharp-shinned and Cooper’s hawk. Both of these species seldom appear above treetop, instead wandering streamside thickets to ambush their victims with a sudden burst of speed. Short wings and long rudder-like tails are perfect for expertly navigating between tree trucks and under shrubbery.

For other raptors, their attention since the winter solstice turned to courtship and by the end of January, the top predator of the riparian corridor, the great horned owl, will be on eggs. Utilizing an old crow or hawk nest, these owls have timed their nesting to coincide with the emergence of young squirrels and other mammals in the woodlands, easy food for a growing brood of young owls. Another early nester along the waterways of the Front Range is the bald eagle. No other species exemplifies the successful protection of our riparian spaces than this species, which also benefits of course by the removal of key pesticides that interfered with their ability to produce viable eggs.

As the day length gradually increases the chickadees begin singing their territorial songs, and the birds that joined them for the winter begin departing and also practicing their songs for their return to their home territories. Waterfowl, too, are leaving in pursuit of thawing lakes and marshes. Robins and downy woodpeckers will be on eggs before full leaf-out. It will not be long before the songbirds that left for western Mexico and Central America will be arriving to take advantage newly emerging insects in the bank-side vegetation. But in the meantime, consider visiting some greenways along the Front Range to brighten a winter day. Some recommended places to explore include the Wheat Ridge Greenbelt, the Bobolink/South Boulder Creek trail, and the Poudre Trail in Fort Collins. Visit www.coloradocountybirding.com for directions and site descriptions.