Many mammals such as wolves and lions are pack hunters. Many fish and cetaceans also collaborate to herd shoals into bait balls, then eat them. So why are there no flock-hunting birds of prey?
鈥� Your questioner is mistaken in believing that there are no flock-hunting birds of prey. The Harris鈥檚 hawk (Parabuteo unicinctus) is well known to hunt in family groups of up to 14, but typically only five or six, in much the same way as the land mammals cited. This practice suits birds hunting in the desert and dry scrub landscapes of the hawk鈥檚 typical habitat. Harris鈥檚 hawks ambush prey by chasing their quarry into a group of waiting birds. During the chase, any hawk can take over when the leader gets tired or is thrown off course. They are reputed to be the most successful predators on the planet in terms of ratio of kills to hunting attempts, and share their spoils among the group.
鈥淭he Harris鈥檚 hawk is well known to hunt in family groups in much the same way as land mammals鈥�
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Because of a gregarious nature, they have been widely adopted as falconry birds 鈥� they are relatively easy to breed in captivity and can be trained to attack a variety of game. They are sometimes flown by falconers in a 鈥渃ast鈥� of two birds, or even three, to take advantage of their natural behaviour.
David Ridpath, Drybrook, Gloucestershire, UK
鈥� I visited a falconry near Perth, UK, a few years ago and was introduced to Oscar, a Harris鈥檚 hawk that was adept at working with novice falconers. A falconer told me that these hawks are unusual in that they hunt in flocks, and that this might be the source of their flexibility and social intelligence in working with humans. I recall walking up a hill and being surprised to find Oscar walking beside me. I was told he probably only wanted a lift to the top, and I let him stand on my glove. When I got to the crest, he took off again. He was obviously as tired as I was.
Robert Williams, East Croydon, Surrey, UK
鈥� My observations on our farm over many years indicate that birds of prey do collaborate and enjoy potential 鈥渕eals鈥�. I have seen wedge-tailed eagles work in pairs to stalk wild ducklings in open paddocks. Even though the ducklings were in the care of their parents and the adult ducks tried to protect their young, they were no match for the eagles.
We regularly observe crows acting in packs to secure their next meal, especially at lambing time. A number of crows will stand a short distance from a ewe with a very young lamb, patiently waiting for either the lamb to wander off from its protective mother, or the ewe to wander off without the lamb for water or to feed. If either happens, they act quickly and attack the lamb. I have also observed dozens of crows in a flock chasing small mobs of ewes and young lambs in open paddocks, trying to separate them and attacking any lambs that lag behind. Is this why a group is called 鈥渁 murder of crows鈥�?
鈥淚 have observed dozens of crows in a flock chasing small mobs of ewes and young lambs in paddocks鈥�
Anna Butcher, Brookton, Western Australia
鈥� The American white pelican (Pelecanus erythrorhynchos) will gather in flocks to herd fish if the water is shallow. When the water is deeper, the birds will usually hunt as individuals.
David Rubin, Ballston Lake, New York, US
鈥� Cooperative hunting in packs is actually rare among mammals, and seems to occur in intelligent and socially complex species in which the bond between related animals persists into adulthood. Hence, it is far more common for mothers and subadult offspring to hunt together. The most familiar pack hunters are wolves, lions and orcas.
For this type of hunting to be a benefit, the target must offer a more substantial reward than anything within the grasp of a single animal. Birds are not as physically robust as terrestrial animals and will not usually target prey larger than themselves, so the cost of sharing normally exceeds the benefit of hunting as a group. It is possible to imagine scenarios in which cooperation would pay off for some bird species, but evolution has no imagination and cannot plan ahead.
Christine Warman, Hinderwell, North Yorkshire, UK
This article appeared in print under the headline 鈥淧reying alone鈥�