Harmony and Conflict in the Living World - Alexander F. Skutch [35]
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Blue-tailed Bee-eaters, Merops superciliosus
taining more than a single pair, at least when roosting at night, are Splendid Blue Wrens, Blue-tailed Bee-eaters, Long-tailed Titmice, and hanging parakeets. Cold weather often induces clustering by birds that ordinarily avoid contact with each other.
Among the bonds that hold social animals together, not the least important is reciprocal preening or grooming. Probably the majority of birds preen only themselves. Others, including pigeons, parrots, toucans, and many more preen their mates, especially about the head and neck, where the feathers are inaccessible to a bird's own bill. But in the most sociable of all, members of a flock
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appear to preen one another indiscriminately. When anis perch in a row, any one may nibble the feathers of any other. In the days when the valley where I live was still wild, Marbled Wood-Quails, now so rare and shy that they are seldom seen, were so tame that I could sometimes watch them for long intervals while standing unconcealed only a few yards away. They were especially easy to observe when they foraged at the woodland's edge. After scratching for food among fallen leaves, to the accompaniment of soft, melodious, contented notes, a covey of six began to put their feathers in order. Three rested close together on a low branch, alternately billing one another's plumage, chiefly on the head and abdomen. The one in the center performed this service for its companions on either side, who reciprocated the favor; and sometimes an outside bird reached past the central one to bill the plumage or legs of the quail on the other end. Presently a fourth bird jumped up to join the preening party on the branch, while the remaining two were similarly engaged on the ground. None tried to dominate another (Skutch 1983).
Among primates, mutual grooming is a prominent activity that probably helps to counteract the disruptive aggressiveness of some species, particularly baboons. So important is mutual grooming to male lemurs that their dentition has been highly modified to facilitate this activity: the front teeth of the lower jaw project forward as a sort of comb, which appears so poorly fitted for biting or chewing that it puzzled naturalists until they discovered that it serves excellently for grooming (Jolly 1967). The true monkeys and apes work over one another's pelage with their fingers rather than their teeth, removing dirt and external parasites. This widespread primate habit persists among humans with inadequate facilities for washing. In the highlands of Guatemala, where cold air and rarity of large streams discourage bathing, I used to see Indian women sitting in the doorways of their huts, diligently searching their children's hair for lice or whatever infested it. Horses, although imperfectly social, nibble each other simultaneously, mostly on the withers at the posterior end of the mane. My stallion and mare regularly exchanged this courtesy after their evening meal; yet, far from being
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a perfect gentleman, he would drive her from her bananas if he finished before she did.
Not only does help in body maintenance bind social animals more closely together; it may even draw animals of diverse kinds together. A number of birds regularly pluck parasites from the bodies of large mammals. In Africa, two species of sharp-toed oxpeckers, belonging to the starling family, persistently climb over the bodies of rhinoceroses, zebras, domestic cattle, and other herbivores, relieving them of the ticks and other pests that supply most of these birds' food. In the Americas, cowbirds of several species perform the same service for cattle and for free animals such as Capybaras and tapirs. Similarly, the Egyptian Plover plucks parasites from the