Raptors come in all shapes and sizes, and most are not a threat to healthy adult waterfowl, even small species like teal. Of the many factors that influence what raptors eat, size is the most important. The sizes of raptors and their prey are directly related. For example, with a wingspan of seven feet, golden eagles are the largest raptors in North America and can easily take cackling geese, while smaller bald eagles cannot. At the other end of the spectrum, green-winged teal see northern harriers as enough of a threat that they take flight when these medium-size raptors approach. Mallards, which are significantly larger and heavier than greenwings, typically show little concern when harriers pass by.
While it's energetically advantageous for raptors to take large prey, the potential benefits must be balanced with the risk of going after something too big. Researchers in California recounted observing a golden eagle that attempted to grab a Great Basin Canada goose, somewhat larger than the cackling geese these raptors readily prey on. In this instance, after the eagle failed to secure the goose by the back, the goose grabbed the eagle with its bill and gave it several good whacks with its wings. The two birds parted ways with neither showing signs of injury, but if the goose had squarely landed a blow and broken one of the eagle's hollow wing bones, the raptor would have likely perished as a result.
Being hunters ourselves, man has long been in awe of the enviable predatory skills and aerial capabilities of raptors like eagles and falcons. While many children dream of becoming a fighter pilot when they grow up, most of us never realize that ambition. But regardless of our age, we can still live the dream by thoughtfully watching and vicariously flying along with the raptors that we see while visiting wetlands and other wild places.
Raptors, Ducks, and Habitat
While it would be easy to assume that fewer raptors would mean more ducks, no studies have indicated that these birds take enough waterfowl to significantly depress their populations. Waterfowl and raptors have shared the same habitats for hundreds of thousands of years, and in healthy ecosystems both groups of birds thrive in "the balance of nature." Like most predators, raptors tend to take the small and the weak. For example, a study of crippled mallards in Wisconsin found that most of the birds were killed by predators, and raptors including red-tailed hawks, northern harriers, and great horned owls accounted for about half of the predation.
By managing healthy ecosystems, we can help ensure that the balance of nature is maintained. Some specific management practices include:
- Minimizing encroachment by trees on the prairies, where raptor numbers were historically limited by a lack of perching sites.
- Managing healthy prairie uplands and wetlands to provide secure cover for nesting hens and broods.
- Maintaining shrubby vegetation like buttonbush in forested wetlands to provide cover for wood duck ducklings.
- Avoiding habitat loss and wetland drawdowns that concentrate waterfowl and expose them to increased risk from raptors and other predators.
—Scott Yaich, Ph.D., Ducks Unlimited Director of Conservation Operations