Stolen: Cormorants hit the High Country |

Stolen: Cormorants hit the High Country

by Joanne Stolen

For the past several weeks, we have seen Cormorants on Dillon Reservoir. I don’t recall having ever seen them in past years. Apparently they are wide ranging, and the double-crested cormorant, which is probably what these were, has one of the widest range and greatest adaptability of any North American cormorant. Cormorants are found on lakes and reservoirs in eastern Colorado in the summer, and a few have been reported at higher elevations – including some at nearby Antero Reservoir in South Park. Many migrate to Texas or Mexico, but a few remain in Colorado in winter. Apparently the population is increasing nationwide, and that is perhaps why we are starting to see them on Dillon Reservoir.

These sea birds are very distinctive in that, when they are in the water, only their long necks stick out – sort of like a periscope of a submarine. They have a strange hook at the end of their bill. When they fly, it takes a lot of effort to get off the water. There is a lot of intense flapping as they skim a long ways over the top of the water before they slowly rise up. Apparently, nature somehow did not give them a lot of oil in their feathers, and they actually get waterlogged. This predicament may be good for diving but not so good for flying when wet. In New Jersey, where I use to live, they are like the crow of the estuaries: big and black or dark brown, and they hang around in flocks. You can see them lined up on docks and pilings with wings outspread, sometimes in regular formation, like large black statues, or some sort of strange gargoyle. They spread their wings to dry them out after diving and fishing. Sometimes there are so many it looks like they are having a convention or meeting. They are large birds. They reach up to a length 36 inches with a wingspread of 54 inches and weigh 4 to 6 pounds.

They dive and swim around in pursuit of prey, and can dive to depths of 25 feet below the water’s surface. Generally they stay under the water less than 30 seconds but are capable of staying submerged up to 70 seconds. When diving, they propel themselves with their feet.

They build large, shallow nests on the ground or in trees. The male and female both participate, and it takes an average of four days to build the nest. It’s a joint effort, with the male building the foundation and bringing the material in for the female to continue building. It’s like the female is responsible for the designing. The male will add to and reinforce the nest throughout the season. Old nests are often rebuilt and used for four years or more. When they are built in trees, nests are often made of natural materials like twigs, roots, weeds, vines, and plant debris. For some reason, nests found on the ground contain a lot of random debris left about by us humans. The female lays two to seven chalky-blue eggs sometime between April and July, and both parents take turns incubating them. The young are fed regurgitated food by reaching into the parent’s gullet or by picking up disgorged food. When they are three to four weeks of age, the young wander from the nest, and gather in bands and socialize.

I mentioned that they are strange gargoyle-like creatures. Apparently they have ancestors that existed in the time of the dinosaurs, and the very earliest known modern bird, had essentially the same physical appearance as the cormorant!

Breckenridge resident Dr. Joanne Stolen is a former professor of microbiology from Rutgers now teaching classes at CMC. Her scientific interests are in emerging infectious diseases and environmental pollution.

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