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Brachylagus idahoensispygmy rabbit

By Ashley Rohde

Geographic Range

Pygmy rabbits live throughout most of the Great Basin area and, to a lesser extent, in nearby intermountain areas of the western United States. They are found from the southwest corner of Montana north and east through southern Idaho and southern Oregon. Distribution also extends south to northern Utah, northern Nevada, and Eastern California. There are also populations in east-central Washington and Wyoming that are genetically isolated. (Sayler, et al., 2001)

There is some evidence that the geographic range of pygmy rabbits has diminished within the last 3000 years. Fossil evidence and the constant reduction of sagebrush habitat, the habitat type that is necessary for pygmy rabbit survival, provide strong evidence that the prehistoric range was much larger than it is currently. (Lyman, 1991)

Habitat

Brachylagus idahoensis are found primarily in big sagebrush (Artemisia tridentata) habitat and secondarily in communities dominated by rabbitbrush (Chrysothamnus spp.). More rarely they are found in areas of abundant greasewood (Sarcobatus spp.). They have also been found in areas with the woody plants antelope bitterbrush (Purshia tridentate), threetip sagebrush (Artemisia tripartita), gray horsebrush (Tetradymia canecens), and prickly phlox (Leptodactylon pungens). Grasses they are associated with include thick spike wheatgrass (Elymus lanceolatus), palins reedgrass (Calamagrostis montanensis), sedges (Carex spp.), prairie junegrass (Koeleria macratha), and several others. (Lyman, 1991)

Pygmy rabbits can be found from 4,494 to more than 7,004 feet (1,370 to 2,135 meters) in Nevada and from 4,986 to 5,298 feet (1,520 to 1,615 meters) in California.

  • Range elevation
    1370 to 2135 m
    4494.75 to 7004.59 ft

Physical Description

Brachylagus idahoensis is the smallest rabbit species in North America and fit easily in the palm of a hand. They weigh between 246 to 462 grams, averaging 398 to 436 g. They are 23.5 to 29.5 cm long, with a tail length of 15 to 24 mm and hind foot length of 67 to 76 mm. Their fur color varies from brown to dark grey with white around the margins of their short, round ears. Their ears and feet are densely covered in hair and they have a very short tail. Rabbits in general show some sexual size dimorphism, in that females are 1 to 10 percent larger than males. (Chapman and Feldhamer, 1982; Green and Flinders, 1980; "Information from Pacific Biodiversity Institute's Endangered Species Information Network", 2004)

  • Sexual Dimorphism
  • female larger
  • Range mass
    0.4 to 0.46 kg
    0.88 to 1.01 lb
  • Range length
    23.5 to 29.5 cm
    9.25 to 11.61 in
  • Average basal metabolic rate
    2.145 W
    AnAge

Reproduction

Mating systems in pygmy rabbits are unknown. In the related genus Sylvilagus, males maintain sexual hierarchies, with dominant individuals mating with more females. (Chapman and Feldhamer, 1982; Chapman and Feldhamer, 1982)

There is little known about the reproductive habits of pygmy rabbits. The breeding season is short, compared to other rabbits, occurring from March to May in Idaho and February to March in Utah. It has been suggested that young are raised in nests inside burrows, though none have been found. Pygmy rabbits appear to synchronize breeding throughout the breeding season. Breeding time is determined by female readiness, which seems to be influenced by photoperiod and the condition of local food plants. Gestation is unknown, but lasts from 27 to 30 days in Sylvilagus species. Average litter size is 6. There is a maximum of three litters in a breeding season. Pygmy rabbits are capable of reproduction in the year following their birth. (" Information from Pacific Biodiversity Institute's Endangered Species Information Network", 2004; Chapman and Feldhamer, 1982; Green and Flinders, 1980)

  • Breeding interval
    There is a maximum of three litters in each breeding season.
  • Breeding season
    Breeding occurs from March to May in Idaho and February to March in Utah.
  • Range number of offspring
    4 to 8
  • Average number of offspring
    6
    AnAge
  • Range gestation period
    27 to 30 days
  • Range age at sexual or reproductive maturity (female)
    11 (high) months
  • Range age at sexual or reproductive maturity (male)
    11 (high) months

There is little known about parental investment among pygmy rabbits. In other rabbit species females build nests for their young and care for them until they are mature. (Chapman and Feldhamer, 1982)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

Little is known about the lifespan of pygmy rabbits. Lifespans of related rabbit species vary greatly. Pygmy rabbit lifespan is primarily limited by predation, which can claim up to 88% of all individuals including adults and juveniles. Maximum mortality occurs between birth and 5 weeks old. (" Information from Pacific Biodiversity Institute's Endangered Species Information Network", 2004; Conaway and Wight, 1962)

Behavior

Pygmy rabbits are the only rabbit species in North America to dig their own burrows. Burrows are dug in deep loose soil and are extensive, with multiple, interconnecting chambers. They also use natural cavities and the burrows of other animals. Burrows have several entrances, usually at the bases of large sagebrush shrubs. Pygmy rabbits use a system of runways between food plants, both above ground in the summer and below the snow in winter. They move by scampering close to the ground and generally don’t leap. (Duszynski, et al., 2005; Green and Flinders, 1980)

Home Range

Pygmy rabbits are not territorial and their home range is generally determined by food availability. (Lyman, 1991)

Communication and Perception

Brachylagus idahoensis produce several vocalizations characterized as squeals, squeaks, and chuckles. They squeal when alarmed. Male pygmy rabbits also communicate dominance through body signals. It is likely that chemical cues play a role in communication, as in other mammals, but this is poorly understood in pygmy rabbits. (Chapman and Feldhamer, 1982; Duszynski, et al., 2005; Green and Flinders, 1980)

Food Habits

Pygmy rabbits are herbivorous grazers that eat mostly sagebrush (Artemisia spp.). During winter months their diet consists of up to 98% sagebrush. In the summer and spring months their diet becomes more varied, including more grass and new foliage. (Green and Flinders, 1980; Sayler, et al., 2001)

  • Plant Foods
  • leaves
  • roots and tubers
  • wood, bark, or stems
  • seeds, grains, and nuts

Predation

Pygmy rabbits are preyed upon by weasels (Mustela), coyotes (Canis latrans), badgers (Taxidea taxus), bobcats (Lynx rufus), diurnal birds of prey (Falconiformes), owls (Strigiformes), foxes (Vulpes and Urocyon cinereoargenteus), and sometimes humans (pygmy rabbits are sometimes difficult for hunters to distinguish from other rabbit species). Predation is the primary cause of mortality among both adults and juveniles and can be as high as 50% in the first five weeks of life. Like other rabbits, pygmy rabbits mainly try to stay hidden and are cryptically colored to avoid predation. They are also capable of short bursts of speed to try and escape predators. ("Wildlife Distribution and Occurrence", 1991; Chapman and Feldhamer, 1982)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Brachylagus idahoensis is a prey source for many predators (listed above) but dwindling populations make them scarce game. It is possible that the burrowing and grazing habits of these rabbits have an advantageous effect on at least one species of sagebrush plants (Artemisia tridentate), which are their primary food source. (Lyman, 1991)

  • Ecosystem Impact
  • creates habitat

Economic Importance for Humans: Positive

Pygmy rabbits are important and unique members of the ecosystems in which they live.

Economic Importance for Humans: Negative

Pygmy rabbits have no known negative economic impact on humans.

Conservation Status

Washington state lists B. idahoensis as an endangered species and it is believed that there are less than fifty left, maybe none left in the wild. Breeding and reintroduction programs to date have been mostly unsuccessful. Washington pygmy rabbits are a genetically distinct subspecies and, therefore, conservationists are not trying to crossbreed them with larger populations elsewhere. Pygmy rabbits are also a species of concern in Idaho. ("Wildlife Distribution and Occurrence", 1991; Sayler, et al., 2001)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Ashley Rohde (author), Kalamazoo College, Ann Fraser (editor, instructor), Kalamazoo College.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

folivore

an animal that mainly eats leaves.

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

herbivore

An animal that eats mainly plants or parts of plants.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

2004. "

Information from Pacific Biodiversity Institute's Endangered Species Information Network
" (On-line image). Endangered Species Information Network. Accessed October 15, 2005 at http://www.pacificbio.org/ESIN/Mammals/PygmyRabbit/pygmyrabbit.html.

Pacific Biodiversity Institute. 2004. "Information from Pacific Biodiversity Institute's Endangered Species Information Network" (On-line). Endangered Species Information Network. Accessed October 15, 2005 at http://www.pacificbio.org/ESIN/Mammals/PygmyRabbit/pygmyrabbit.html.

1991. "Wildlife Distribution and Occurrence" (On-line). Accessed October 15, 2005 at http://www.fs.fed.us/database/feis/wildlife/mammal/brid/wildlife_distribution_and_occurrence.html.

Chapman, J., G. Feldhamer. 1982. Wild Mammals of North America, Biology, Management, Economics. Baltimore, Maryland: The Johns Hopkins University Press.

Conaway, C., K. Sadler, D. Hazelwood. 1974. Geographic Variation in Litter Size and Onset of Breeding in Cottontails. Journal of Wildlife Management, 27: 171-175.

Conaway, C., H. Wight. 1962. Journal of Wildlife Management. Onset of Reproductive Seasonand First Pregnancy of the Season in Cottontails, 26: 278-290.

Duszynski, D., L. Harrenstien, L. Couch, M. Garner. 2005. A Pathogenic New Species of Eimeria from the Pygmy Rabbit, Brachylagus idahoensis in Washington and Oregon, with Discription if the Oocyst and intestinal Endogenous Stages.. Journal of Parasitology, 91: 618-623.

Green, J., J. Flinders. 1980. Brachylagus idahoensis. Mammalian Species, 125: 1-4.

Lyman, R. 1991. Late Quaternary Biogeography of the Pygmy Rabbit (Brachylaus idahoensis) in Eastern Washington. Journal of Mammals, 72: 110-117.

Sayler, R., L. Shipley, R. Westra. 2001. "Behavior, Dispersal and survival of captive-raised Idaho pygmy rabbits (Brachylagus idahoensis) released onto the INEEL in Idaho." (On-line). Accessed October 15, 2005 at http://www.stoller-eser.com/NERP/pygmy.htm.

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