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. 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. 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. Mallards, which are significantly larger and heavier than greenwings, typically show little concern when harriers pass by. 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. 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. The sizes of raptors and their prey are directly related. Of the many factors that influence what raptors eat, size is the most important. Raptors come in all shapes and sizes, and most are not a threat to healthy adult waterfowl, even small species like teal. One recent study in Prairie Canada found that red-tailed hawks were the primary cause of mortality in hen pintails from May to mid-July. Early breeding Pintails, however, often nest in short grass or crop stubble, where they are more easily seen by raptors. Hens of many duck species also avoid detection by nesting in dense stands of tall grass or shrubs that provide overhead cover. Males of many duck species also lose their bright coloration and assume hen-like eclipse plumage while they are flightless during the summer molt. Because female ducks are particularly vulnerable to predation while incubating their eggs, having drab, brown plumage helps them avoid detection from above. Studies show that the brighter the plumage of potential prey, the greater their chance of being spotted and taken by a raptor. Of course, one of the best ways to avoid becoming prey is to avoid being seen in the first place. They were much less worried about me than about the falcon. The ducks I watched that day simply refused to fly, even when I walked to the edge of the pond. Capable of reaching speeds of 200 miles per hour while in a 'stoop,' peregrines are the avian equivalent of a Ferrari. Peregrines (once called duck hawks) prefer to grab or knock down birds (as large as mallards and pheasants) in the air, so the instinctive response of waterfowl is to stay on the water when one of these falcons is spotted. Returning to those ducks I was watching on the pond in January, a peregrine falcon causes the opposite reaction. And if raptors are sufficiently abundant or persistent, individual birds can become separated from their mates or family groups. While effective, this strategy consumes valuable time and energy. Similar to schooling fish, this flocking behavior confuses raptors by making it more difficult for them to focus on a single target. When threatened by bald eagles or northern harriers, green-winged teal and cackling geese take to the air, make several tight circles as a flock, and then return to their original location when the perceived danger has passed. Waterfowl use a variety of tactics to elude raptors. Waterfowl also select wetland habitats that provide them with greater protection from raptors and move to new habitats where raptors are less prevalent. For example, researchers observed that gadwalls wintering in Louisiana increased their feeding activity at night to avoid harassment by northern harriers (once called marsh hawks) during daylight hours. The threat posed by raptors can affect waterfowl behavior in many ways. That means something that we can see at a distance of 100 yards, a raptor can see from a mile awayor a mile up.

Hawks have, on average, five times more photoreceptors in their eyes than humans, giving them visual acuity estimated to be 10 times greater than our own. In fact, these birds may have the keenest vision in the animal kingdom. The amazing eyesight of raptors is difficult for humans to comprehend. That's exactly what the ducks I was watching one sunny January day were worried about as they nervously eyed the peregrine falcon circling high over their pond. Imagine a living missile armed with long, sharp hooks and guidance systems locked onto you, coming out of the sky at nearly 200 miles per hour.

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