Q. I saw a red-tailed hawk fly into a tree and knock a squirrel into the street right in front of me. A second red-tail swooped down and picked up the squirrel by the time it hit the ground. This is mating season for hawks. Would a mated pair work cooperatively to do something like that?
A. I asked ornithologist Peter Stangel what he thought. He said, “I suspect this was fortuitous. The first bird tried and failed to catch the squirrel, and the second was just in the right place at the right time. But, there are isolated instances of red-tails cooperating when hunting squirrels. It would be really interesting to see if you observe this behavior again – if you do, that would make a stronger case for cooperative hunting by this pair. Cooperative hunting by Harris’s hawks is well-documented in the Southwest.”
Harris’s hawks are a relatively common bird of prey in the southwestern United States from Texas to the Arizona deserts. Their geographic range extends thousands of miles farther south to Chile. These western raptors are the only birds of prey in the world to have been documented scientifically to hunt in packs. As many as a half dozen Harris’s hawks hunt together, singling out and surrounding an escaping mammal. Visions of these aerial wolfpacks probably give jackrabbits nightmares.
Cooperative predation by birds was documented convincingly for the first time by James C. Bednarz in “Science” magazine in 1988. According to the author, “Individuals coordinate actions such that the probability of successful capture of one large prey item [to be] shared among all participants is increased.” Bednarz’s study was impressive in itself. He used radiotelemetered hawks to follow their behavior in a New Mexico desert. The raptors were unquestionably working as an organized unit to track their prey. He noted that cooperative hunting “has been reported almost exclusively for social mammalian carnivores.”
Everyone knows social mammals such as wolves and lions cooperate to capture prey. Many people in southern coastal areas know about strand feeding, the remarkable fish-catching behavior demonstrated by bottlenose dolphins. A pod of dolphins will corral a school of fish, propelling them toward shore. When the fish jump out of the water to escape, the dolphins do belly slides and end up amid the fish, eating those flopping around. Humpback whales have an unusual form of prey capture known as bubble netting. As many as two dozen whales swim together in a circle deep below the ocean's surface while blowing bubbles. The rising air forms a cylinder of bubbles through which the thousands of fish inside will not pass. The trapped fish make easy pickings for the whales swimming up through the bubble net with open mouths.
I once saw a dramatic confrontation between two mammal species with cooperative hunting behavior – spotted hyenas and African wild dogs. I was watching a wild dog pack chase a herd of impalas when I looked behind the dogs and saw several hyenas gaining on them. Hyenas will follow wild dogs that are chasing prey and then move in, robbing the dogs of their kill. African wild dogs, however, behave like a superorganism. Several of the dogs turned and formed a group. Then, as if a leader had said Charge, away they went headlong toward the hyenas. A hyena can beat a dog one-on-one but not a dog pack working in unison. The hyenas dispersed, choosing not to take on this well-trained platoon. The dogs returned to a meal of fresh impala.
Clearly, mammals have evolved some highly effective cooperative hunting behaviors. Such practices may be more common among other animals, including birds, than we are aware. Perhaps such behavior has simply not yet been observed. Perhaps it has been observed but has not been recognized as intentional behavior among the subject animals. The phenomenon should of course be familiar to all of us: The most cooperative hunters in the world are humans.