Raptors are common predators of waterfowl in many areas of North America
Photo by Eric Reuter
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. 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.
Peregrine falcons are part of a bird group called raptors, which includes eagles, falcons, hawks, and owls. Most are hunters, and they come well equipped. Their primary weapons are large feet and long, incredibly strong toes tipped with sharp, curved talons, all adapted for piercing, gripping, and killing prey. Raptors also have sharp, cutting beaks for plucking feathers or fur from their prey and tearing off bite-sized chunks of flesh. Some raptors' beaks have special adaptations, depending on their particular feeding habits and hunting techniques. For example, falcons have notches on their bill that are used to sever the spinal cord in their quarry's neck, causing almost instant death and thereby reducing their risk of injury from flailing prey.
The amazing eyesight of raptors is difficult for humans to comprehend. In fact, these birds may have the keenest vision in the animal kingdom. 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. That means something that we can see at a distance of 100 yards, a raptor can see from a mile away—or a mile up. For waterfowl, that's a serious concern.
The threat posed by raptors can affect waterfowl behavior in many ways. 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. Waterfowl also select wetland habitats that provide them with greater protection from raptors and move to new habitats where raptors are less prevalent.
Waterfowl use a variety of tactics to elude raptors. 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. Similar to schooling fish, this flocking behavior confuses raptors by making it more difficult for them to focus on a single target. While effective, this strategy consumes valuable time and energy. And if raptors are sufficiently abundant or persistent, individual birds can become separated from their mates or family groups.
Returning to those ducks I was watching on the pond in January, a peregrine falcon causes the opposite reaction. 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. Capable of reaching speeds of 200 miles per hour while in a "stoop," peregrines are the avian equivalent of a Ferrari. The ducks I watched that day simply refused to fly, even when I walked to the edge of the pond. They were much less worried about me than about the falcon.
Of course, one of the best ways to avoid becoming prey is to avoid being seen in the first place. Studies show that the brighter the plumage of potential prey, the greater their chance of being spotted and taken by a raptor. Because female ducks are particularly vulnerable to predation while incubating their eggs, having drab, brown plumage helps them avoid detection from above. Males of many duck species also lose their bright coloration and assume hen-like eclipse plumage while they are flightless during the summer molt.
Hens of many duck species also avoid detection by nesting in dense stands of tall grass or shrubs that provide overhead cover. Early breeding pintails, however, often nest in short grass or crop stubble, where they are more easily seen by raptors. 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.