Grooming (zoology)

Grooming is the process of cleaning and maintaining an animal's hair, fur, or body, and it serves several purposes. It is health-related because the activity cares for the skin, feathers, or fur. Grooming also serves a social function. Between members of a community, grooming reduces stress, communicates and signals social status, spreads pheromones, achieves thermoregulation, relieves pain, increases or decreases arousal, self-stimulates, and prevents sexually transmitted diseases.

As grooming is similar through the various levels of animal taxa, it has been conjectured that grooming behavior is evolutionarily ancient. Most animals (mammals, birds, and insects) groom by moving their limbs over their own bodies or mouthing or licking their bodies. In some birds, sand bathing is quite common. Chickens, for example, enjoy dirt baths which are part social ritual as well. With fish, a species with no limbs, it is not uncommon to see them rubbing or simply moving against rocks, branches, or sand, generally accomplishing what a sandbath does for a bird.

A bird preening its feathers, a cat licking its paws, or a bear brushing his back against a tree truck are all self-grooming. This is where the animal, alone, takes care of the grooming behavior without help from another animal. However, mutual grooming is quite common. In mammalian species, this is a form of displayed behavior, which helps to cement the social bonds between members of the group. Yet another kind of cleaning behavior, called cleaning symbiosis, occurs between certain species of fish and shrimp. Here, one species will eat the parasites off another species. The cleaner gets food, the recipient remains debris- and parasite-free.

Grooming as Cleaning Behavior

Observations and experiments performed on laboratory rats showed that pregnant rats spent an increasing proportion of their time grooming their ventral surface, which includes the nipple lines and anogenital areas. When the rats were fitted with collars so they could not reach these regions, their mammary development was inhibited. The conclusion to be drawn from this is that self-stimulating grooming is a necessary part of the preparation process for nursing.

A similar conclusion was reached when looking at the function of grooming in male rats. Prepubertal males engaged in self-grooming of the anogenital area more than their female counterparts. When collars restricted the rats from grooming, their sexual development was significantly hampered. Again, the conclusion is that male rats needed to perform self-stimulating autogrooming to prepare for reproduction.

Another very important fact about self-grooming behavior is the appearance of a grooming pattern. For example, depending on the species, self-grooming may start around the head area and progress downward until the entire body has been groomed. In experiments, it has been noted that a particular animal will not vary its grooming pattern. Studies on hamsters show that specific grooming tendencies evolve as the animal matures. Certain types of grooming behavior are always the result of some external stimuli, or they are the consequence of an aspect of the animal’s natural behavior. A male rat invariably performs genital grooming after copulation. A dog, when aroused by some external stimuli (fear or excitement), will often groom its genitalia for de-arousal. Many animals, when afraid or nervous, will gnaw on their paws. Pigs often chew on other pigs’ tails, it is thought when they are bored or have an excess of nervous energy. The expression “licking one’s wounds” originates from the observation that most animals will tend to an injury by licking the area, spreading an antiseptic found in saliva to reduce pain and decrease the chances of infection. Insectivores, like solenodons and shrews, spend much time grooming, using only their hind legs, to ensure thermoregulation.

One of the most well-known animal groomers are cats. Cats lick themselves as their primary form of cleaning their bodies. It is estimated that most cats spend between 30 and 50 percent of their day grooming themselves. They are also highly averse to water baths, so this form of self-cleaning is necessary. It is also an evolutionary tool, as cats often clean themselves after eating in order to rid their bodies of the scent of their prey or catch. Furthermore, like other mammals, cats use grooming and licking as displacement behavior, a way of alleviating stress, anxiety, and boredom.

Regardless of the lack of similarity between grooming species, grooming behavior is remarkably similar, reiterating that there has not been much diversification in the evolution of grooming behavior. Sea lions, seals, and walruses, regardless of whether the pelage is sparse or dense, spend much time grooming. This is typical of marine mammals. They accomplish this by a doglike scratching motion with their hind flippers and using their fore flipper to rub their head and neck while balancing on the other front flipper. They also nibble on their fur, much like dogs. It is common for these animals to rub against rocks or each other, similar to the activity of bears when they rub up against trees. Fish will also use this rubbing behavior against rocks or coral to scour their bodies free from debris.

Grooming as Social Behavior

Mutual grooming, also called allogrooming or allopreening, is when an animal cares for the body surface of another. Mutual grooming in animals is more a form of communication, a social act, than it is a cleansing one. Researchers have come to this conclusion because the time allocated to mutual grooming exceeds what is necessary for simple cleansing and sanitation. This behavior, especially in primates and social birds, promotes social bonding and establishes and maintains the hierarchy among community members. Littermates from a dog or cat litter often participate in allopreening throughout their lifespans.

Mutual grooming also brings attention to whether there is such a thing as animal altruism, which is the selfless delivery of service from one animal to another. Whenever one observes a parent grooming their young, the conclusion is that the motive behind the act is to tend to the health of the infant or young, which promotes the proliferation of the species. Nearly all mammals and many species of birds display this behavior. With marsupial births, the young of the Virginia opossum are in a semiembryonic state. The mother licks the embryon at birth so that the membrane encasing it will break. She then licks a trail from the birth canal to the pouch so that the neonate, using its developed olfactory senses, can find its way to the pouch without further aid from the mother. In altricial and semialtricial placental mammals, the young are usually born naked or with little fur. Most of these animal types, such as cats, dogs, mice, shrew, rats, and hamsters, lick the newborn to remove the birth membrane, break the umbilical cord, and eat the placenta after birth. They lick the newborn to clean the perineal region and to remove urine and feces, also aiding in thermoregulation.

When one observes animals and birds of a similar peer group performing grooming rituals, what appears to be unilateral or altruistic grooming behavior may, in fact, be mutual aid in that, over the long term, repayment may be expected. It is the expectation of reciprocation that establishes and maintains social status. For example, studies on nonhuman primates (mostly Old World monkeys such as rhesus macaques, stump-tailed macaques, and baboons) have shown that competition exists among group members for animals considered to be excellent groomers. Alliances are formed between groomer and groomed; the groomed may provide excellent protection or be a skilled food gatherer. There is evidence of ranking among members of primate society, and mutual grooming appears to assist in maintaining the social order and structure.

In primates that form consortships (Cercepethecines), or mating relationships, grooming is important in the copulatory sequence, which is not the case in primates that do not form consortships. In general, sexual grooming serves as a male strategy to increase the receptivity of an estrus female. In olive baboons and hamadryas, there is a high correlation between the age of the male and the grooming of the females, implying that this may be an alternative method of securing female cooperation in mating when direct agonistic approaches fail or are no longer an option.

Equids are well-known for mutual grooming. Horses, zebras, and similar animals groom each other by pairing off and standing nose-to-nose or head-to-tail, scratching and nibbling each other’s neck, back, and tail with their teeth. The nose-to-nose greeting and rubbing of noses is also typical of tapirs and rhinoceros.

Interspecies Grooming

Humans have successfully exploited the horses’ need for bonding through touch and grooming. Trainers often start training horses in spring when the animals are shedding. By brushing and grooming, the trainer develops a friendship and level of trust with the animal. This is an example of interspecies bonding through grooming. This behavior is widely noticed in any combination of humans, dogs, and cats. Sometimes licking another animal or human is simply a show of affection.

Symbiotic grooming, briefly mentioned above, occurs among some species where they pair off to assist one another in the grooming process. Pilot fishes and remoras are commensal fishes (a type of symbiosis) that attach themselves to sharks and other fish. Apart from eating the remnants of the host’s meal, they also feed on the external parasites that plague the host fish. Fleas and lice are symbiotic groomers as they eat harmlessly on dead skin or feathers of mammals and birds.

Grooming behavior is an integral part of existence for all higher-order animals. It is such an important part of human behavior that if proper grooming is not taught at an early age and not performed, there are negative repercussions from peers and society in general. Grooming is such an important part of human society that in the United States alone, the annual sales of men’s and women’s toiletries is a multibillion-dollar industry. Scientists have only recently begun to study grooming behavior closely.

Principal Terms

Allogrooming: mutual grooming or grooming between two individuals

Altruism: a behavior that increases the fitness of the recipient individual while decreasing the fitness of the performing individual

Consortship: a pairing of a male and a female

Pheromone: a chemical produced by one individual that influences the behavior of another individual of the group

Symbiosis: a relationship between two species of organisms which is not necessarily advantageous or disadvantageous to either organism

Thermoregulation: the process by which animals maintain body temperatures within a certain range

Bibliography

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