After nesting in thickets along the shores of alpine lakes, Wilson's warblers are descending from the Colorado mountains and have been turning up in Metro Denver over the past week; this morning, I discovered a female on our Littleton farm.
These small, brightly colored warblers nest across Canada and Alaska and southward through the ranges of the American West. Insectivores, they prefer willow thickets that line streams, ponds and lakes, where their nest is placed in low shrubs or directly on the ground. They generally arrive along the Front Range urban corridor in early-mid May and soon head for higher terrain, often spending the summer near timberline.
Retreating from the alpine and subalpine zones as the first snows dust the higher peaks, Wilson's warblers move across the Colorado Piedmont in late summer, heading for wintering grounds in Central America; there they feed in tropical forests, coastal wetlands or mangroves. When you consider the Temperate forests, desert canyons and lowland swamps that they visit during migrations, one concludes that few birds utilize such a wide variety of natural habitat in the course of a year.