Spring 2012 Magazine
The Dalliance of the Eagles
From "The Dalliance of the Eagles" by Walt Whitman
Late winter is a good time to be writing about golden eagles in New Mexico. Although it is 18 degrees and snowing hard today, golden eagles around the state have been building or remodeling nests or eyries for weeks and most will be incubating eggs by the end of the month. They need an early start as they may spend nearly half the year preparing for, raising and tolerating young in their territories. They will spend as much as six weeks sitting on eggs. The hatched eaglets will spend 10 to 12 weeks in the eyrie before fledging. The young will gradually move further from the nest over the following weeks and months. It does not appear that young are driven from the territory by parents, but move on their own to find new feeding areas. From this point, and for the next four years, the birds disperse. Studies in Idaho suggest that the young may range furthest in their first couple of years. As they approach breeding age, in their fifth year, they may return closer to their natal range. Sporting an adult plumage and having honed their hunting skills, they are ready to compete for nest sites and mates.
In New Mexico the favored nest sites are cliffs. Just about any place in New Mexico that has cliffs and open ground where prey can be found will serve as golden eagle habitat. Once golden eagles mate they will stay together throughout the year. They defend a territory that may range from 100 to 146 square miles. They may use the same nest year after year. In fact some nest sites have been used repeatedly for many decades. These nests can acquire great size with annual remodeling. The female, usually about 25% larger than the male, will lay one to three eggs. Two eggs are by far the most usual. After hatching, the male provides virtually all the food for the first month but by six weeks post-hatching the female shares equally in providing food. Breeding success appears to be closely linked to numbers of principal prey species. In Idaho peak numbers of jackrabbits are positively correlated with unusually high incidence of three-chick broods. Golden eagles are opportunistic hunters using a wide variety of food sources. In Raptors of New Mexico, edited by Jean-Luc E. Cartron, 33 species of prey have been documented in the golden eagle diet. If a pair is nesting in prairie dog country, prairie dogs will make up a large part of the diet. Even coots, ducks, geese and fowl as large as sandhill cranes can be on the menu. Some of you may have seen the YouTube video of a Golden Eagle taking down a cow. This is not typical but they are known to prey on domestic animals. Although domestic animals appear to be a very small percentage of their diet, sheep and calf remains have been found at nest sites.
How many golden eagles are there in New Mexico? It depends on the time of the year. While our breeding golden eagles remain in their territories all year, every winter we play host to migrating eagles that come from as far away as Alaska. Estimates of New Mexico resident pairs are 275 to 406. Breeding Bird Survey data indicates a decline in New Mexico. A current, long term study, Results of the 2010 Survey of Golden Eagles in the Western United States, prepared by Western EcoSystems Technology, Inc., for the U.S. Fish and Wildlife Service, indicates a decline in golden eagles in the Southern Rockies/Colorado Plateau. HawkWatch International conducts annual surveys and also reports declining numbers in the region. This is a trend we need to watch closely.
The Wildlife Center is playing a small part in tracking golden eagles in a collaborative project among the U.S. Fish and Wildlife Service, New Mexico State University, Dale Stahlecker, an independent contractor, and Grace, our educational golden eagle. Grace was found on the Navajo Nation in October 2010. She had an eye injury and all of her tail feathers had been pulled out. The injury to her eye was so severe the eye had to be removed. As a result she could not be released.
Grace is helping attract wild eagles so they can be banded and fitted with satellite transmitters. These transmitters have little solar panels on them that allow long-term GPS tracking. The information gained from these transmitters will show us ranges, nest site locations, migration paths, survival rates and much more. This information can then be correlated with prey base abundance, climate factors, and human disturbance such as wind farm construction or resource extraction. Grace is doing her part to help us understand and address the challenges facing her magnificent species.
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