Double-crested cormorants have returned to Front Range lakes and reservoirs over the past week, among the earliest summer residents to arrive from their wintering grounds. These large, dark-colored, aquatic birds may be seen alone when fishing but are generally encountered in flocks, especially at their roost and nesting sites.
Indeed, this most common and widespread cormorant in North America nests in colonies, usually placing their bulky nests in a grove of trees but sometimes directly on the ground. They prefer islands or narrow peninsulas along lakes where, over the years, their copious guano kills the trees; once this occurs, the flock will choose another site or simply nest on the ground. Feeding primarily on fish, cormorants are superb divers, equipped with heavy bones and reduced oil on their feathers; due to the latter trait, their plumage gets wet and they often perch on logs, islands, tree limbs or man-made structures with their wings spread to dry.
The interior population of double-crested cormorants has increased dramatically over the past half century, partly due to the large number of reservoirs that now dot the Midwest and Great Plains. Those that summer along the South Platte Valley winter in Texas or eastern Mexico; arriving in late March or early April, they will depart for southern climes by mid November. If conditions remain mild and open water is available, a small number may stay in Colorado for the winter months.
