Sometimes birding experiences lead to a much broader thought process that brings history, ecology, habitat availability, land-use practices, conservation, and population-dynamics together in an on-going conversation and environmental process. Case in point, ever-expanding Bald Eagle populations. During this century, Bald Eagles have steadily been expanding their nesting range from their traditional forest and lakes habitats and riverside woodland nesting areas onto the open plains and agricultural areas.
I have long wondered when a pair of Bald Eagles would move into my neighborhood in south-central North Dakota. There are certainly some attractive deep lakes a few miles north of here now, formed just 20 years ago by an epic spring runoff that turned a few shallow wetlands into 25-foot-deep lakes, now with healthy fish populations. Each spring I have hoped to find the first eagle-nest in the area, but by late April, I give up on the prospect of a nearby Bald Eagle nest. But last week, a friend texted me a short video of his discovery — an active Bald Eagle nest with an attentive adult pair and three half-grown nestlings! Gracias Jason!
So it finally happened! The nest site is about 15 miles southeast of my office in quite an unexpected location. The nest-site very much resembles that of a Swainson’s Hawk, or a Red-tailed Hawk rather than a stately Bald Eagle’s choice. Built in a pretty intense agricultural area, with corn popping out of the field where the long row of shelterbelt trees hosts a large cottonwood tree where the eagles built their eagle-sized nest — much bigger than any hawk’s. The one habitat area that would seem most attractive to the eagles would be a small reservoir with scattered trees located a mile north of the nest, although the area surrounding the small lake is a recreation area with periodic family-fishing activities. Even so, the eagles would mostly have the area to themselves, or at least to share with ducks, geese, grebes, cormorants, and pelicans — some of which may be potential prey.
I do get the impression that these prairie eagles are less fish-based so far as their prey preferences go. These adaptable Bald Eagles appear to be hunting medium-sized birds and mammals in their nesting territories. Obviously, Jason’s pair of eagles are excellent hunters within their agricultural territory, raising the maximum brood of three nestlings to a near-fledging stage — very impressive, considering that you might think this mostly agricultural landscape would be a less than optimum area for hunting Bald Eagles.
What’s an optimum area? Traditionally it has been woodlands on the edge of a big lake or a complex of lakes, where the eagles catch fish — or a woodland bordering a river that likewise provides good fishing opportunities for these “fish eagles.” But Bald Eagles are really showing their adaptability as they move onto the open plains. Similarly, I found a few scattered Bald Eagles nesting in central and north-central Nebraska, where there were more prairie grasslands than ag fields.
Since the 1980s, we have seen the comeback and expansion of the range of nesting Bald Eagles across North America — a direct result of the passage of the Endangered Species Act in 1973 and the outlawing of extreme pesticides (organochlorines DDT, DDE, and Dieldren) in 1972. The pesticides affected populations of many avian predators, especially fish-eating birds such as Bald Eagles, Ospreys, and Brown Pelicans, along with Peregrine Falcons and others. After the United States and Canada banned these poisonous pesticides, the intensely affected bird populations began to slowly recover — and they continue to continually expand their ranges today.
During a recent discussion with my primary university professor, Jim Grier, who studied nesting Bald Eagles in Ontario and Manitoba for more than four decades, we visited about the on-going expansion of nesting Bald Eagles into the Great Plains. In this region, the historic records of nesting Bald Eagles came from the primary rivers. Early explorers traveled along the major rivers and did not venture far from these water highways, primarily due to the inherent dangers on the open plains at that time. The diaries of Lewis and Clark and John James Audubon, in the first and fourth decades of the 19th Century respectively, reported Bald Eagle nests along the Missouri River, but there was never any information about the birds more than a short distance from the riverbanks. Before nesting Bald Eagles were eliminated from North Dakota and most of the Great Plains, we have no historic perspective about how widespread Bald Eagles might have been on the open plains.
So today, we’re seeing an expansion of nesting Bald Eagles, and possibly a re-population of the Great Plains. Certainly, there is a different habitat mix today, and Jason’s nest is clearly in the most agricultural location I can imagine for nesting Bald Eagles. Historically, there was pure prairie covering the region into the 1880s, so today’s eagles are using a much different habitat mix than their historic counterparts would have used — even on the same geographic locations. There are large tracts of native prairie just three miles west of this nest; will eagles move into this Coteau region, dotted with marshes and lakes soon?
Actually, I’m hoping this is the newest step of expansion of a Bald Eagle population on its way to filling in the space between here and the Missouri River, about 80 miles to the west. In the meantime, I’m excited at the new addition to the nesting birds in the region, and I will enjoy monitoring the new eagle nest — this year, and hopefully for many years to come. I’ll keep you posted on it, for sure.