Pikas

(Ochotonidae)

Class Mammalia

Order Lagomorpha

Family Ochotonidae

Thumbnail description
Small, egg-shaped herbivores with prominent round ears, small eyes, and no visible tail

Size
5–8 in (13–20 cm); 3–10 oz (80–300 g)

Number of genera, species
1 genus; 30 species

Habitat
Talus, meadow, and steppe

Conservation status
Extinct: 1 species; Endangered: 1 species; Vulnerable: 3 species; Lower Risk/Near Threatened: 2 species; Data Deficient: 2 species

Distribution
Mountains of western North America; primarily high mountains and steppe of central Asia

Evolution and systematics

Molecular evidence indicates that the family Ochotonidae (pikas) separated from the family Leporidae (the other family in the order Lagomorpha) 37 million years ago. Paleontological evidence closely matches this date, suggesting that the two families separated in the early Oligocene. All evidence points to an Asian origin for the family. Pikas spread to North America by the late Oligocene. Pikas quickly differentiated into many forms and became particularly diverse during the Miocene. During this time, representative genera were found in North America, Asia, and Africa. The first Ochotona appeared in the early Pliocene of Asia, and Ochotona first entered North America in the mid-Pliocene. Ochotona and Prolagus, the only other pika genus to reach historical times, are first found in Europe during the late Pliocene. Prolagus subsequently went extinct, leaving Ochotona as the only living representative of the family from a record of 25 fossil genera.

The close resemblance of all pika species makes it difficult to find external characters to tell them apart. Even using traditional morphological measurements on skull bones and dentition has not been sufficient to stem controversy over the systematic alignment of pika species; no two revisions of the genus are the same. Some subspecies have landed in as many as four different species. Molecular techniques have begun to clarify pika systematics, and a consensus is nearing, although the task is far from completed. Currently, 30 species of Ochotona are recognized.

Physical characteristics

All living pikas are very similar in appearance. They are small egg-shaped balls of fluff sporting thin, relatively large round ears and without a visible tail. Pikas range in size from the Gansu pika (Ochotona cansus), which weighs in at approximately 3 oz (80 g), to Glover's pika (O. gloveri), which can reach 10 oz (300 g). Most pikas are a brownish gray, and accents are most often in the red spectrum.

Distribution

Ochotona has a northern, Holarctic, distribution. In North America, they are found primarily at high elevations throughout the inter-montane west (American pika, O. princeps) or in the mountains of Alaska and the Yukon (collared pika, O. collaris). The remainder of the genus is found throughout central Asia, in the Himalayan massif and associated ranges, and across eastern Siberia to Sakhalin Island and onto Hokkaido Island, Japan. The steppe pika (O. pusilla) reaches west to the Ural Mountains, and one small population found to the west of this chain can be classified as European.

Habitat

There are two types of pikas: those that occupy rocks or piles of talus and those that live in meadow or steppe environments and construct burrows. This contrast in habitat type determines all aspects of behavior and reproduction in pikas, such that these traits are best treated together for each ecological type of pika.

Behavior

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

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 long-call, 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 animal 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 affiliative 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

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

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.

Feeding ecology and diet

Like all lagomorphs, pikas are generalized herbivores. Their most characteristic feeding behavior is the gathering of vegetation during summer that is stored in a centralized cache, or haypile, to serve as food during winter. Again like all lagomorphs, pikas excrete two types of feces and commonly reingest the soft viscous feces.

Pikas are most active during the mid- to late summer when they begin to gather vegetation with which to construct their haypile. At this time, a flurry of activity ensues with animals sometimes making one round-trip per minute to the adjoining meadow to pluck a long stem of a succulent herb. Commonly, a pika will sit on a rock briefly, utter a short call to proclaim its territory, rush to the meadow for a mouthful of vegetation, rush back, deposit the load, quickly give another call, and rush off again. The haypiles constructed by members of a pair are normally located on their territory closer to the territory of their pair mate rather than centered on their territory. Pikas forage for vegetation off of the talus, generally

close to the talus-meadow interface. Their behavior when feeding contrasts sharply with that of when they are gathering hay. Feeding pikas pluck individual small stems, generally of grass, which they eat while maintaining an alert posture; they appear to be extremely wary of predators while feeding. Pikas gather vegetation for their haypiles at far greater distances from the talus and, in contrast to their alert posture while feeding, appear foolhardy and unaware of predators while gathering hay. They try to get the largest mouthful of vegetation that they can, often diving at the base of a forb to clip it off.

Reproductive biology

Rock-dwelling pikas produce few young each year, whereas burrowing forms produce many large litters each season.

Most pikas originate from first litters as there is strong selection pressure for young to become active as early in the short summer season as possible. Juvenile pikas must grow up fast, claim a vacant territory (if one exists), and construct a haypile before the next winter's snow descends on the talus. Young normally remain close to their site of birth, and dispersal to a territory far away on their home talus, or movement to another talus patch, is rare.

Young become independent approximately three weeks after parturition, and they remain on their family burrow system territory throughout the summer and the following winter. Thus, as litter after litter appear on the meadow, the number of animals in each family grows and the overall population density skyrockets. Some populations reach densities of more than 120 animals per acre (300 per ha). Mortality is high during the harsh Tibetan winters and most animals perish; it is rare for any pika to live into its second year. The breeding season begins in early spring, and this is also the time that the composition of families is determined. There is a modest reshuffling of pikas before mating occurs. Nearly all pikas born the preceding summer remain on their home territory, but some, in particular males, disperse short distances and join neighboring families. The most common movements are to an immediately adjoining neighbor, but some pikas move as far as five territories away. The result of most of these movements is an equalizing of density across the meadow. Males do not move to families with more females. Instead, they move to families with more males.

The mating system expressed by plateau pikas results from the combination of the random nature of over-winter mortality and the few dispersal movements of animals alive just before the mating season. Most family burrow systems are occupied by a single adult male and female, which results in monogamy. However, when the number of surviving males and females is higher than can be accommodated on the restricted number of territories by only pairs, more complex situations arise. Some families are composed of one male and many females (polygyny), others with multiple males and one or more females (polyandry). These three different mating systems can occur in neighboring family burrow systems, a

situation unique in mammals. In addition, the formation of these mating systems does not appear to result from variance in habitat quality on the meadow; there is no correlation between the type of mating system on a burrow system in one year with what will appear there the following year.

Conservation status

Twenty-six of the 30 pika species have been fully assessed for their IUCN Red List conservation status, and of these, six (23%) have been classified as Threatened (O. argentata, O. hoffmanni, O. huangensis, O. iliensis, O. koslowi, and O. pusilla). The first five on this list live in remote areas and are poorly known. The steppe pika (O. pusilla) has retreated as its habitat has been plowed under. An additional four species have one or more threatened subspecies. In nearly all cases, these forms are threatened because of habitat loss or inadvertent poisoning (control efforts directed at other, more common, pika species).

Significance to humans

Direct economic benefits from pikas are few; they are too small to serve as a source of country food. In central Asia,

their pelts were once used to make felt. A distillate of the soft feces of pikas ("mumio") is used as a folk medicine in central Asia to speed up the healing of broken bones or to remedy rheumatism. Some species are believed to be agricultural pests or to damage rangelands and are subject to widespread poisoning efforts. A contrasting view is that these species are important in their respective ecosystems and should be preserved to maintain local biodiversity rather than to be subject to control.

Species accounts

List of Species

American pika

Ochotona princeps

taxonomy

Ochotona princeps (Richardson, 1828), Rocky Mountains, Canada. Thirty-six subspecies.

other common names

English: Cony, whistling hare, rock rabbit.

physical characteristics

Moderate sized, with short ears and egg shaped body. Body is 6 to 8.5 in (162–216 mm). Buffy pelage; it lacks the grayish collar and the white ventral pelage found on the only other North American pika (the collared pika).

distribution

Found primarily at high elevations throughout the intermontane west of North America. Many of the 36 subspecies correspond to populations from isolated mountain ranges.

habitat

A characteristic rock-dwelling species.

behavior

Males and females defend individual territories of approximately equal size. These territories are relatively large, and normally only about six animals will occupy 1 acre (15 per ha).

feeding ecology and diet

Generalized herbivores.

reproductive biology

Rock-dwelling pikas produce few young each year (normally only two or three offspring), but normally only two are weaned

successfully. They mate early in the spring. All adult females initiate two small litters during each short summer season. If the first litter is successful, then the second litter is abandoned. If the first is claimed by a weasel or lost because the female was in poor physiological condition coming out of the long winter, then the second litter as a back up is produced. Gestation is approximately 30 days, and young normally become surface active about a month after parturition.

conservation status

Several isolated subspecies are considered Vulnerable to extinction.

significance to humans

None known.

Plateau pika

Ochotona curzoniae

taxonomy

Ochotona curzoniae (Hodgson, 1858), Chumbi Valley, Tibet, China. No subspecies.

other common names

English: Black-lipped pika.

physical characteristics

Body length 4.7–9.8 in (12–25 cm); weight 0.4 lb (200 g). Brownish fur. The nose has a blackish tip and the lips form an indistinct black ring.

distribution

Confined to the high alpine meadows of the Qinghai-Xizang (Tibetan) plateau.

habitat

Alpine meadow habitat across the Tibetan plateau.

behavior

The basic unit of social organization is the family unit that occupies a communal burrow system on alpine meadow habitat. These territories form a matrix of adjoining families, and the average spacing between the centers of activity of these territories is approximately 75 ft (25 m). Location of family burrow system territories is relatively stable on the meadow from year to year, however their composition may vary dramatically. Extremely social: as the density builds within a family burrow system during summer, the frequency of affiliative behavior soars. Rates of behavior may be as high as one social encounter per minute. These behaviors are complemented by a rich vocal repertoire (whines, trills, muffle calls) that appears to initiate many of these social encounters. In contrast to these social behaviors seen within families, most behaviors between individuals from different families are aggressive, long chases and fights.

feeding ecology and diet

Generalized herbivores that eat a wide variety of grasses, sedges, and forbs that grow on the high alpine meadows of the Tibetan plateau. The lack of a snowpack on the plateau allows them to forage year-round, and thus they are one of the few pika species that does not build a conspicuous haypile.

reproductive biology

Different mating systems exist yearly, relating to current populations of local territories. Have a high rate of reproduction. During the spring to summer breeding season mothers initiate many sequential litters at three-week intervals. Most mothers wean three large litters (up to eight young), while others may produce up to five litters in a year.

conservation status

Not threatened.

significance to humans

Treated as a pest species for nearly four decades, it is believed that they cause rangeland degradation and eat vegetative resources that could better be utilized by local livestock (primarily yak and sheep). As a result, this species has been poisoned extensively. In Qinghai Province alone, pikas have been poisoned over 80,000 mi² (200,000 km²), and the onslaught continues. Unfortunately, loss of the plateau pika over vast expanses of the Tibetan Plateau has resulted in a loss of many native species that rely on the pika. Most endemic native birds nest only in pika burrows, and when these collapse following poisoning, the birds disappear. Most predators on the plateau (weasels, ferrets, Pallas's cat, Tibetan fox, wolf, brown bear, upland buzzard, saker falcon, and black-eared kite) rely almost exclusively on pikas in their diet. When the pikas are poisoned, these animals also disappear. Thus, it appears that the plateau pika is a keystone species for biodiversity on the plateau and should be managed accordingly. Fortunately, as of 2002, the tide has been turning toward a policy that embraces the pika rather than one bent on destruction of the species.

Large-eared pika

Ochotona macrotis

taxonomy

Ochotona macrotis (Günther, 1875), Tibet, China. Four subspecies.

other common names

None known.

physical characteristics

Body length 5.9–7.9 in (15–20 cm). A generalized ochotonid, but with large thin ears. Brown coat with gray undercoat.

distribution

High mountains of central Asia; has been recorded as high as 20,100 ft (6,130 m).

habitat

A typical rock-dwelling pika; it lives in high mountains.

behavior

Adults live in pairs.

feeding ecology and diet

A generalized herbivore, some do not cache vegetation in haypiles, a characteristic of most pika species; it is felt that the lack of snow in parts of their range allowing for year-round foraging may be responsible.

reproductive biology

Monogamous. Typical of most talus-dwelling pikas, they produce few (generally two) small litters (three to five young) per year.

conservation status

Not threatened.

significance to humans

None known.

Northern pika

Ochotona hyperborea

taxonomy

Ochotona hyperborea (Pallas, 1811), Chukotsk Peninsula, Russia. Seven subspecies.

other common names

English: Siberian pika.

physical characteristics

A generalized ochotonid with no obvious external discriminating characteristics. Medium brown with orange to buffy under parts.

distribution

Largest distribution of any pika species; found across most of eastern Siberia to Sakhalin and Hokkaido islands.

habitat

A typical rock-dwelling pika, although throughout much of its range it also is known to inhabit tree-falls, stumps, and mossy banks.

behavior

Adults live in pairs, although they rarely interact.

feeding ecology and diet

Forages on grasses and other vegetable matter; constructs large haypiles for winter feeding.

reproductive biology

Assumed monogamous. Most females initiate two litters per summer reproductive season, and most litters range in size from one to five young.

conservation status

Common. However, subspecies on Hokkaido Island, Japan (O. h. yesoensis), are locally considered to be endangered.

significance to humans

On Hokkaido Island, it is an important animal for ecotourism.

Turkestan red pika

Ochotona rutila

taxonomy

Ochotona rutila (Severtzov, 1873), Kazakhstan. No subspecies.

other common names

None known.

physical characteristics

Known primarily for its rich rust-reddish dorsal pelage in summer. Size and weight not available.

distribution

Primarily found in the Parmir, Kirgiz, Gissar, and Tien Shan mountains of central Asia.

habitat

A typical rock-dwelling pika in the central Asian mountains.

behavior

It is unusual among rock-dwelling pikas by having a significantly larger territory on which it forages, and its tendency for juveniles to over-winter on the territory with their parents. Sometimes this is called the "silent" pika, as it has no song or typical alarm call.

feeding ecology and diet

Construct large haypiles. They appear more reticent to forage on open meadows than most pikas, confining most of their foraging to patches of vegetation among the rocks on its large territory.

reproductive biology

Normally two litters are initiated, and litter size is small (two to six young/litter). Mating system may vary yearly depending on populations of local territories.

conservation status

Common, not threatened.

significance to humans

None known.

Pallas's pika

Ochotona pallasi

taxonomy

Ochotona pallasi (Gray, 1876), Kazakhstan. Three subspecies.

other common names

English: Mongolian pika.

physical characteristics

A generalized ochotonid, no strong external discriminating characteristics. Size and weight not available.

distribution

Primarily mountains of western Mongolia and isolated subspecies in Mongolia and northern China.

habitat

Habitat utilization varies across the species. The subspecies O. p. pricei usually occupies arid steppe environments and may construct burrows, whereas the other subspecies are more likely to live in rocky habitats.

behavior

Just as the habitats occupied by Pallas's pika vary, so does the ecology of the species. The marked differences in reproduction, habitat, behavior, and vocalizations may indicate that O. p. pricei will ultimately be treated as a different species. Pallas's pika appears to be an intermediate species (with habitat characteristics between those of the obligate rock-dwellers and the meadow-dwelling burrowing pikas). In these intermediate species, and certainly true for Pallas's pika, the life history features more closely resemble those of the burrowing forms than those of rock-dwelling pikas.

feeding ecology and diet

Known to make large haypiles, although some populations store most of their winter cache under rocks.

reproductive biology

Has a high reproductive rate; several litters may be born per reproductive season, and litter sizes may be large (one to 13 young per litter). Mating system may vary yearly depending on populations of local territories.

conservation status

Common, species-wide. However, two subspecies are threatened with extinction: O. p. hamica (IUCN status: Critically Endangered) and O. p. sunidica (IUCN status: Endangered).

significance to humans

O. p. pricei has been considered a focus for plague and subjected to control efforts. This activity is no longer being pursued.

Afghan pika

Ochotona rufescens

taxonomy

Ochotona rufescens (Gray, 1842), Kabul, Afghanistan. Two subspecies.

other common names

None known.

physical characteristics

During summer, it possesses a cream-colored collar that is outlined with russet pelage. Size and weight not available.

distribution

Patchily distributed in the mountains of Iran, Afghanistan, and Pakistan.

habitat

Another intermediate species one that has a tendency to live in rocks, but also constructs burrows. Unlike most alpine pikas,

the Afghan pika may occupy landscapes that are significantly more xeric (dry).

behavior

Its life history characteristics mimic those of the true burrowing forms. It lives in family groups at medium-high densities (up to 30 animals per acre [70/ha]), but it does not have a well-developed vocal repertoire.

feeding ecology and diet

Known to eat thistles and other xeric plants. They make large hay piles, but normally collect these stores twice per year (in spring before the vegetation dries up and again in fall when the vegetation is revived by seasonal rains).

reproductive biology

Have a high rate of reproduction; females may produce up to five litters in an extended breeding season, and litter sizes may contain as many as 11 young. Mating system may vary yearly depending on populations of local territories.

conservation status

Not threatened.

significance to humans

Considered a threat to agricultural crops and orchards throughout much of its range, and as a consequence has been subject to control programs.

Gansu pika

Ochotona cansus

taxonomy

Ochotona cansus Lyon, 1907, Gansu, China. Three subspecies.

other common names

None known.

physical characteristics

Very small, with adults weighing only about 3 oz (80 g). Otherwise, it is typical of most ochotonids. Brownish fur is lighter below.

distribution

Distributed throughout the north-central Tibetan Plateau.

habitat

Lives in shrubby habitats, largely dominated by Potentilla fruticosa and Caragana spp., under which it constructs burrows.

behavior

The ecology and behavior of the Gansu pika closely resembles that of the plateau pika; it has a vocal repertoire of four calls.

feeding ecology and diet

A generalized herbivore.

reproductive biology

Two or three litters are produced during a breeding season that extends from early April until late August. Litter sizes range from one to six young. Mating system may vary yearly depending on populations of local territories.

conservation status

Common, species-wide. However, one subspecies is threatened with extinction (O. c. sorella; Endangered); and another is Data Deficient (O. c. morose).

significance to humans

None known.

Steppe pika

Ochotona pusilla

taxonomy

Ochotona pusilla (Pallas, 1769), Orenburgsk Obl, Russia.

other common names

English: Little pika.

physical characteristics

Body length is 5.9 in (15 cm). Color is darker grayish brown above, lighter below. A small generalized ochotonid.

distribution

Found from the Ural Mountains east across southern Russia and northern Kazakhstan.

habitat

Occupies flat meadow and steppe country where it utilizes burrows.

behavior

The ecology and behavior of the steppe pika closely resemble that of the plateau pika. The steppe pika is the only truly nocturnal pika. One of its key characteristics is the loudness of its short call, which can be heard over very long distances.

feeding ecology and diet

A generalized herbivore that constructs haypiles.

reproductive biology

Have a high reproductive rate; three to five litters are produced per year and litter sizes may contain as many as 13 young. Mating system may vary yearly depending on populations of local territories.

conservation status

Vulnerable.

significance to humans

None known.

Resources

Books

Averianov, A. O. "Mammals from the Mesozoic of Kirgizstan, Uzbekistan, Kazakhstan and Tadzhikistan." In The Age of Dinosaurs in Russia and Mongolia, edited by M. J. Benton, M.A. Shishkin, D. M. Unwin, and E. N. Kurochkin. Cambridge: Cambridge University Press, 2000.

Chapman, J. A., and G. A. Feldhamer, eds. Wild Mammals of North America. Baltimore: Johns Hopkins University Press, 1982.

Chapman, J. A., and J. E. C. Flux, eds. Rabbits, Hares and Pikas: Status Survey and Conservation Action Plan. Gland, Switzerland: IUCN, 1990.

Cheeke, P. R. Rabbit Feeding and Nutrition. Orlando, FL: Academic Press, Inc., 1987.

Hoffmann, R. S., and A. T. Smith. "Lagomorphs." In Mammal Species of the World: A Taxonomic and Geograhic Reference, Vol. 3, edited by D. E. Wilson and D. M. Reeder. Washington D. C.: Smithsonian Institution Press, in Press.

Li, C-K., R. W. Wilson, M. R. Dawson, and L. Krishtalka. "The Origin of Rodents and Lagomorphs." In Current Mammalogy, Vol. 1, edited by H. H. Genoways. New York: Plenum Press, 1987.

Myers, K., and C. D. MacInnes, eds. Proceedings of the World Lagomorph Conference. Guelph, Canada: University of Guelph, 1981.

Smith, A. T. "Population Structure in Pikas: Dispersal versus Philopatry." In Mammalian Dispersal Patterns: The Effects of Social Structure on Population Genetics, edited by B. D. Chepko-Sade and Z. T. Halpin. Chicago: University of Chicago Press, 1987.

Thompson, H. V., and C. M. King, eds. The European Rabbit: The History and Biology of a Successful Colonizer. Oxford: Oxford University Press, 1994.

Periodicals

Averianov, A. O. "Phylogeny and Classification of Leporidae (Mammalia, Lagomorpha)." Vestnik Zoologii 33 (1999): 41–48.

Cao, Y., M. Fujiwara, M. Nikaido, N. Okada, and M. Hasegawa. "Interordinal Relationships and Timescale of Eutherian Evolution as Inferred from Mitochondrial Genome Data." Gene 259 (2000): 149–158.

Dobson, F. S., A. T. Smith, and X G. Wang. "Social and Ecological Influences on Dispersal and Philopatry in the Plateau Pika." Behavioral Ecology 9 (1998): 622–635.

Dobson, F. S., A. T. Smith, and X. G. Wang. "The Mating System and Gene Dynamics of Plateau Pikas." Behavioural Processes 51 (2000): 101–110.

Hedges, S. B., and S. Kumar. "Divergence Times of Eutherian Mammals." Science 285 (1999): 2031a.

Huchon, D., et al. "Rodent Phylogeny and a Timescale for the Evolution of Glires: Evidence from an Extensive Taxon Sampling Using Three Nuclear Genes." Molecular and Biological Evolution 19 (2002): 1053–1065.

Killian, J. K., R. R. Buckley, N. Stewart, B. L. Munday, and R. L. Jirtle. "Marsupials and Eutherians Reunited: Genetic Evidence for the Theria Hypothesis of Mammalian Evolution." Mammalian Genome 12 (2001): 513–517.

Liu, F-G. R., and M. M. Miyamoto. "Phylogenetic Assessment of Molecular and Morphological Data for Eutherian Mammals." Systematic Biology 48 (1999): 54–64.

Kumar, S., and S. B. Hedges. "A Molecular Timescale for Vertebrate Evolution." Nature 392 (1998): 917–920.

Murphy, W. J., E. Elzirik, W. E. Johnson, Y. P. Zhang, O. A. Ryder., and S. J. O'Brien. "Molecular Phylogenetics and the Origins of Placental Mammals." Nature 409 (2001): 614–618.

Swihart, R. K. "Body Size, Breeding Season Length, and Life History Tactics of Lagomorphs." Oikos 43 (1984): 282–290.

Organizations

IUCN Species Survival Commission, Lagomorph Specialist Group. Department of Biology, Box 871501, Arizona State University, Tempe, AZ 85287-1501 USA. E-mail: a.smith@ asu.edu Web site: <http://www.ualberta.ca/dhik/lsg>

Other

IUCN—The World Conservation Union, Species Survival Commission, Red List Programme Office. Official IUCN Red List of Threatened Species. <http://www.redlist.org>.

Andrew T. Smith, PhD