The number of bald eagles observed in early January along a stretch of the Missouri River was down significantly compared to past years.
Patrick T. Isakson, nongame biologist for the North Dakota Game and Fish Department, said 12 bald eagles were counted during the annual mid-winter survey, an area of the river covered from Bismarck to the Garrison Dam. The average number of bald eagles observed during the past decade is 43. Last year, the survey was canceled due to the weather, while in 2008 a record 85 were tallied.
The number of bald eagles wintering in the state depends on the amount of open water and availability of prey. “Approximately 90 percent of the river is now covered with ice, which limits the number of ducks and geese in the state,” Isakson said, while mentioning that waterfowl is a main food source for wintering eagles this time of year.
Eagles are relatively easy to spot, as they prefer to perch in large cottonwood trees along the river. Adult bald eagles have a white head and tail and a dark brown body, while immature bald eagles are brown with irregular white plumage. Adults gain their full plumage at three years of age. Golden eagles have a gold cap on their head.
Each winter biologists nationwide conduct similar surveys to estimate the number of bald eagles wintering in the lower 48 states. Each state completes the survey as close to the target date as possible to make certain that birds are not counted twice.