In general, rock-dwelling pikas are territorial as individuals or in pairs, relatively asocial (most are quite pugnacious), have a restricted recorded vocal repertoire of two calls, are long-lived (some reaching six years of age), and have relatively

A Daurian pika (Ochotona dauurica) emerging from its hole. (Photo by Fletcher & Baylis/Photo Researchers, Inc. Reproduced by permission.)

stable low-density populations over time. In contrast, burrowing pikas that occupy meadow or steppe habitats live in family burrow system territories, are extremely social, communicate by uttering a number of different vocalizations, have short adult life spans, and their populations undergo extreme annual fluctuations in size and may reach densities of up to 120 animals per acre (300/ha).

One similarity between the two types of pikas is the longcall, or song, given by adult males during the breeding season. The long-call consists of many repeated elements in a distinctive pattern for each species. There are, however, clear similarities between these calls in the rock-dwelling American pika (Ochotona princeps) and the burrowing plateau pika (O. curzoniae).

Throughout the day, most pikas are active about one-third of the time, and much of this is spent in quiet repose sitting atop a prominent rock surveying their surroundings. When they do patrol their territory, pikas often rub their cheek gland on rocks to advertise their presence. A quick vigorous chase normally ensues when another pika is encountered on their territory. Sometimes combatants actually make contact, with fur flying from the rump of the interloper. These chases are predictable when the interloper is an animal of the same gender or a non-neighbor of the opposite gender. However, chases are initiated only about half of the time when the an imal encountered is a neighbor of the opposite gender. Otherwise, these opposite-sexed neighbors sit in a limbo of social tolerance, neither chasing nor engaging in any overt affilia-tive behavior that most likely defines a breeding pair.

Interestingly, these territories are not randomly spaced by gender across the talus. Instead, adjacent territories are generally occupied by a pika of the opposite sex. Pikas can live for up to six years of age and thus territory vacancies are uncommon. When they do occur, replacement is an animal of the same gender as the animal that died. Males will not allow settlement next door by another male, and similarly females chase off all available females. Female-female aggression ensures that their spacing is too far apart and the territories on talus are too large for any one male to control access to many females. Pika behavior controls the spacing of animals on the talus, and ultimately leads to a monogamous mating system. These dynamics ensure that the population structure of the pika is relatively stable over time.

Common predators of pikas are weasels and pine martens (genus Mustela). When a pika sees a predator, it utters an alarm call, a repetitive variant of the short call. Martens must capture pikas on the surface of the talus, as they are too big to fit in the cracks and crannies of the talus. When pikas first see a marten, they burst into an alarm call designed to warn neighbors (most of whom are close relatives) of the looming threat. If the predator is a weasel, then the pika often waits a few minutes before first giving the call. Weasels can follow pikas into their lairs in the rocks and, apparently, this latency to call allows the weasel time to clear out of the pika's territory before the pika alerts its neighbors of the threat.

The climate on the Tibetan plateau is frigid during winter and there is usually no snowpack (most precipitation occurs during summer) to insulate animals from these extreme

Pallas's pika (Ochotona paiiasi) near Lake Khovsgol in Mongolia. (Photo by Joy Spurr. Bruce Coleman, Inc. Reproduced by permission.)
A collared pika (Ochotona collaris) eating vegetation in Alaska, USA. (Photo by Frank Krahmer. Bruce Coleman, Inc. Reproduced by permission.)

colds. The high degree of socialization, coupled with the philopatry of juveniles, has led to the conclusion that these family groups are selected to stay together during winter, when huddling may increase their average survivorship.

Nearly all mammalian carnivores and predacious birds on the Tibetan Plateau specialize on eating pikas. In response, plateau pikas utter an alarm call when predators are sighted. But, there are some unusual twists to this behavior. First, the

A northern pika (Ochotona hyperborea) above the timberline. (Photo by © D. Robert & Lorri Franz/Corbis. Reproduced by permission.)

The American pika (Ochotona princeps) uses a "song" to warn others of danger. (Photo by © Robert Lindholm/Visuals Unlimited, Inc. Reproduced by permission.)

call is very faint and barely audible from a short distance away. Apparently, it is designed only to warn immediate family members and not those from neighboring families. Second, the call is only given during the period of the first three days any new litter of juveniles is surface active. Giving the call may bring the predator's attention to the caller, and thus may be costly. After three days on the meadow, the young may be sufficiently experienced and no longer benefits sufficiently from an anti-predator alarm call. At this point, all the animals remain silent until the next litter surfaces.

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