Mutual Grooming
Interactive nibbling between two horses is a common form of mutual grooming (allogrooming). Licking seldom occurs between two mature horses. The two partners usually face each other, standing so that one shoulder is close to the corresponding shoulder of the partner (Figure 11.3). Nibbling of the partner may be prolonged. Feist and McCullough (1976) found the duration ranged from a few seconds to 10 minutes, but in 90 percent of the occasions it lasted three minutes or less.
After introductory sniffing, the grooming activity usually begins along the crest of the neck; it may then proceed to the withers, the shoulder, or along the back to the croup and base of the tail. Sometimes, the horses change sides.
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Mutual grooming occurs primarily on areas of the body not easily reached during self-grooming activities. The dorsal portion of the neck and the withers are usual sites for nibbling. Hechler (1971) found preferences occurred in the following order for Icelandic horses: mane (59.2 percent), withers (18.5 percent), back (9.3 percent), croup (5.8 percent), tail base or dock (4.8 percent), neck (1.7 percent), and shoulder (0.7 percent). Feh and De Mazières (1993) analyzed video recordings of 38 allogrooming sessions to determine the preferred grooming site (base of neck anterior to the with-ers). Then the investigators experimentally groomed that site on other horses by manually imitating the scratching action and rate (2/sec). They found grooming at the “preferred grooming site” reduced the heart rate of the recipient horse, whereas grooming the shoulder (a non-preferred area) did not reduce heart rate.
Horses tend to establish one or a few regular grooming partners. Yet, some horses never seem to allogroom (Wells and Goldschmidt-Rothschild 1979).
In free-roaming herds, mutual grooming is usually only among members of the same social unit. Allogrooming can occur between females, between males and females, and even between males. It is especially frequent among immature horses. The only combination where Feist (1971) did not see mutual grooming within social bands was between herd stallions and foals.
A youngster may seek such interaction, but it is rare for an adult male to reciprocate. Foals tend to mutually groom with other foals (Crowell-Davis et al. 1986). Tyler (1969) observed that between any two partners, the more
Figure 11.3: Mutual grooming (allogrooming).
dominant individual would almost always end a grooming bout; yet domi-nants initiated only 38 percent of the mutual grooming interactions.
In some cases, foals or yearlings approach their mother while she is involved in mutual grooming and proceed to nibble at her. The mare may ignore her offspring or commence nibbling of the youngster instead of the previous partner (Tyler 1969). Mares commonly lick their newborn foals for up to 30 minutes after parturition, but seldom does licking occur thereafter.
Several days after parturition, the mare and foal begin to allogroom. Pre-viously, the foal’s nibbling and chewing on the mare was not reciprocated.
The earliest age for mutual grooming Tyler (1969) observed was between a 6-day-old foal and its mother. Blakeslee (1974) observed an 8-day-old and a yearling in a brief allogrooming bout. By a month of age, foals begin to spend long periods mutual grooming with other foals. This trend seems to increase over the next few months.
The frequency of mutual grooming among group members shows daily and seasonal variation. Keiper and Keenan (1980) noted mutual grooming decreased significantly between 2300 and 0400 hours on summer nights, corresponding to a period when recumbency increased. During the months of spring in southern France, May is the peak month for allogrooming among Camargue mares, stallions, and yearlings (Wells and Goldschmidt-Rothschild 1979). In England’s New Forest, mutual grooming peaks in April and again in July; it is least frequent in September (Tyler 1969). April cor-responds to the shedding of the winter coat, and in July the ponies con-gregate in the shade.
When grouped, the tail switching of horses serves a mutual function to fend off insects. Even pairs of horses occasionally stand side by side fac-ing opposite directions while mutually switchfac-ing the forequarters of their partners. Close body contact facilitates the tail action and reduces body sur-face exposure, Duncan and Vigne (1979) found horses have significantly (P<0.01) fewer biting horseflies on them when they were in large groups and as a consequence fewer bites. Keiper (1979a) noticed an additional strat-egy; ponies while clustered and facing inward took turns circling the other horses using their tails and bodies to brush away insects.
Symbiotic Relationships with Birds and Humans
Mutualistic symbiotic relationships between birds and large animals, such as ungulates, exist on most continents. In such relationships, the birds either seek ectoparasites or obtain insects flushed by movements of the large ani-mals. By eating ticks and biting insects or by scaring away pests, the birds 11 - Comfort Behavior 159
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benefit their symbiotic partners. With horses, such a symbiotic relation-ship occurs primarily with the cattle egret. During horse-egret interactions, the birds sometimes feed while perched on a horse’s back but more often while on the ground. Horses allow the activities of the birds and are not aggressive toward them. The overt passiveness of horses to the physical contact and intimate activities of the birds is evidence that the horses may receive some comfort from the relationship and control their agonistic responses accordingly. Similar passiveness is seen in situations where a horse recognizes a person is swatting and killing horseflies that have just landed or are already biting the horse; yet when such aid is not needed, the same horse may withdraw from human handling.
The mutualistic relationship between horse and mankind is the funda-mental reason these two species formed an association some 6,000 years ago. Horses are capable of being amiable and generally tractable to humans plus provide us many benefits. In turn, horses receive protection, nutritional needs, and care from their owners.