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Tamias merriamiMerriam's chipmunk

By Kim May

Geographic Range

Merriam's chipmunks (Tamias merriami) are distributed throughout central and southern California. In particular, they occurs below 2700 m in the South Coast, Transverse, Peninsular, and Southern Sierra Nevada ranges. (Harvey and Polite, 1999)

Habitat

Merriam's chipmunks occur in habitats that have trees, shrubs, logs, stumps, snags, rocks, and litter. An important factor is understory brush that they use for foraging. These animals inhabit chaparral, oak and pine forests, thickets by streams, and are often found around rock outcroppings. They also inhibit a wide variety of habitats if there are no competing species, such as black bears, mule deer, wild pigs, deer mice, kangaroo rats, and woodrats. (Best and Granai, 1994)

  • Range elevation
    2700 (high) m
    8858.27 (high) ft

Physical Description

Merriam's chipmunks are grayish-brown, with dark stripes of equal width on the dorsal area. The stripes are typically gray or brown, rarely black. The belly and cheeks are white. The tail is long and bushy, and is usually edged with dull white. The average length of the head and body is 134.6 mm. Length of tail is 109.5 mm. The average mass is 71.8 g from males and 77.8 g for females. Hind foot length averages 35.8 mm. The length of the rostrum is 14.1 mm. Braincase length is 24.2 mm. The length of the maxillary tooth-row is 5.9 mm. The length of nasals is 12.1 mm for males and 12.6 mm for females. Width of nasals is 2.5 mm. The depth of the cranium is 14.7 mm. The dental formula for Merriam's chipmunks is i 1/1, c 0/0, p 2/1, m 3/3 = 22. (Best and Granai, 1994)

Merriam's chipmunk seems to follow Gloger's rule. The darker populations occur in the humid coastal areas of the redwood forests from San Francisco Bay southward. The palest populations are in single-leaf pinyon forests in Walker Pass in the semi-arid Kern Basin and on the eastern slope of the Sierra Nevada. (Best and Granai, 1994)

  • Sexual Dimorphism
  • female larger
  • Range mass
    71.8 to 77.8 g
    2.53 to 2.74 oz
  • Average length
    134.6 mm
    5.30 in

Reproduction

The nature of the mating system in T. merriami has not been reported. However, the act of mating has been well described. Females attract males by calling to them. Females call for 10 to 20 minutes intervals. These intervals of calling may take up 3 to 4 hours of a female's day. A male will approach a calling female and perform a display. During this display, the male runs and leaps around the female. Then he will nuzzle his face on the female's face. The female may go into a crouching postion, allowing the male to mount her. In one instance, copulation consisted of four series of pelvic thrusts. There were 12 to 24 thrusts in each series, and each series of thrusts lasted about four seconds. After each series, the male rested and brushed his face side to side on the back of the female's neck. The entire copulation lasted for about 18 seconds. (Callahan and Compton, 1995)

Merriam's chipmunks breed from mid-January to June, with a peak during April. Gestation is about thirty-two days. Average litter size is four, but ranges from three to eight. Females have one litter per year. Mothers spend most of their time with their young for about two weeks. Nests are made in logs, stumps, snags, and burrows. Males that survive the breeding season are usually in poor condition. They will go to their burrows to recover in May and stay there until August or September. (Best and Granai, 1994; Harvey and Polite, 1999)

The young are altricial, and must develop some before they emerge from the natal burrow or nest. At about one month of age, the young are able to leave the burrow. Their movements are uncoordinated, and they do things like go down trees backwards, rather than head-first. It takes about two weeks for them to develop the ability to jump accurately. (Best and Granai, 1994)

There is an extended period of juvenile learning after emergence from the natal burrow or nest. The young go through a predictable pattern of behavioral development, including exploration of the area around their shelter, tandem following, recognition of trails, recognition of food, increased alertness to the mother's expressions, play, increased area of exploration, and development of dominance rankings. (Best and Granai, 1994)

Sexual development is apparently variable. By 11 weeks of independence, the young of the year are about the same size as adults, but maintain a distinct subadult pelage. Puberty is marked in females by a pinkening of the genitals, swelling of the vulva and rupture of the covering membrane. (Best and Granai, 1994)

  • Breeding interval
    Merriam's chipmunks breed once yearly.
  • Breeding season
    Mating occurs from mid-January to June, with a peak of activity in April.
  • Range number of offspring
    3 to 8
  • Average number of offspring
    4
  • Average gestation period
    32 days

The young of this species are altricial, and do not leave the nest until they are about a month of age. When the young chipmunks become active in the nest, their senses are functional. The first day out of the nest, the young will give alarm and agitation calls. It takes about two weeks for the young to develop accuracy in jumping. Young learn how to forage by following their mother around. (Best and Granai, 1994)

  • Parental Investment
  • altricial
  • pre-fertilization
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • protecting
      • female
  • extended period of juvenile learning

Lifespan/Longevity

Merriam's chipmunks can live up to 5 years in the wild. (Best and Granai, 1994)

  • Average lifespan
    Status: wild
    5 years

Behavior

Merriams's chipmunks are diurnal and most do not hibernate. At high elevations, some may hibernate to avoid the snow and cold. During the fall, they collect and cache food, choose a shelter spot, and feed to increase thier mass. During the winter, males form groups and display for precourtsip. Mating continues through spring. In the summer, adults molt and gain weight. (Best and Granai, 1994)

Merriam's chipmunks use woodpecker cavities, natural cavities, and burrows from pocket gophers for night shelter. Most night shelters face east. They usually do not forage more than 300 meters from their night shelter. Merriam's chipmunks travel along tree branches and logs. The trails are communal and are used generation after generation. (Best and Granai, 1994)

Home Range

Most members of this species forage within an range of 300 meters of their night shelter. (Best and Granai, 1994)

Communication and Perception

Merriam's chipmunks use four main calls. The "chuck" has a narrow frequency range and causes others to be quiet and to hide. The "chip" has a wide frequency range and can be located without difficulty. It is usually made by a chipmunk by its den and incites others to call. The "trill" is usually intertwined with the chip and is used for alarm. Lastly, the "chipper" is a series of disorderly notes made from an individual who has been scared and is going for cover. (Best and Granai, 1994)

Scent communication is also important. These animals have functional scent glands by the age of 4 weeks. The vulva emits an odor important for reproduction. Scent marking is common. (Best and Granai, 1994)

In addition, there is tactile communication during mating and between a mother and her offspring. Because the species is diurnal and social, it is likely that visual signals, such as body postures, are also used.

Food Habits

Evidence has shown that Merriam's chipmunks consume more than seventy species of plants. Acorns are a major food source throughout the year. These animals will also consume insects, lizards, muscle tissue of sparrows, seeds found in the feces of goldfinches, and embyronic membrane from eff shells of California quail. (Best and Granai, 1994)

They have two daily forages and a resting period during midday. The first foraging period is in the morning and lasts about three and half hours of constant activity. The second foraging is more relaxed and ends when they goes into their shelter for the night. Searching for food to store in caches takes up most of its active time. Foraging areas are jointly used and there is seldom conflict over food. These animals search for food in forest understory and in trees.

Using their cheekpouches they carry food to another site where they remove the husk and then eat the seeds. If they cache an acorn, they do not remove the husk. They make a pit about 3.8 cm deep and deposit a single acorn. They cover the hole with leaf litter and soil. Merriam's chipmunks also store food in dead logs, between limbs, and branches of trees. When storing food, females generally cache acorns further apart than males. (Best and Granai, 1994)

  • Animal Foods
  • birds
  • reptiles
  • eggs
  • insects
  • Plant Foods
  • seeds, grains, and nuts
  • fruit

Predation

Merriam's chipmunks are prey to several species. These include long-tailed weasels (Mustela frenata), bobcats (Lynx rufus), coyotes (Canis latrans), gray foxes (Urocyon cinereoargenteus), sharp-shinned hawks (Accipiter striatus), badgers (Taxeda taxus), Coopers's hawk (Accipiter cooperii), great horned owls (Bubo virginiana), Pacific rattlesnakes (Crotalus viridis), garter snakes (Thamnophis), gopher snakes (Pituophis melanoleucus), and domestic cats (Felis domesticus). (Best and Granai, 1994; Harvey and Polite, 1999)

Ecosystem Roles

Merriam's chipmunks are prey items for a wide variety of carnivores. They also cache acorns, which may help disperse oak trees. (Best and Granai, 1994)

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Positive

There is no specific information available on this topic. However, these animals are cute and can be entertaining to people who view them scurrying about. Also, they serve as food for predators which people also enjoy watching. Although this does not exactly make Merriam's chipmunks a source of ecotourism, it should be noted that even without substanitial economic impact on humans, there is some human benefit from this species.

Economic Importance for Humans: Negative

This species has no reported negative economic impact on humans.

Conservation Status

Merriam's chipmunks are not listed by CITES or IUCN. (Harvey and Polite, 1999; Best and Granai, 1994)

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Kim May (author), University of Wisconsin-Stevens Point, Chris Yahnke (editor, instructor), University of Wisconsin-Stevens Point.

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.

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

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.

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

granivore

an animal that mainly eats seeds

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.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

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

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

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.

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

Best, T., N. Granai. 1994. Tamias merriami. Mammalian Species, 476: 1-9.

Callahan, J., S. Compton. 1995. Reproductive behavior in Merriam's chipmunk. Great Basin Naturalist, 55/1: 89-91.

Harvey, T., C. Polite. 1999. "California Wildlife Habitat Relationship System" (On-line). Accessed May 07, 2004 at http://www.dfg.ca.gov/whdab/html/M060.html.

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