Thomomys bulbivorusCamas pocket gopher

Geographic Range

Camas pocket gophers (Thomomys bulbivorus) are limited to Willamette Valley, Oregon in the United States and the river drainages from the Yamhill River to the Willamette River system. They are distributed from Portland and Forest Grove south to Eugene, and west to Grand Ronde Valley. (Cassola, 2016; Bailey, 1936)

Habitat

Camas pocket gophers are a fossorial species that inhabit habitats with rich, fertile soil, avoiding coniferous timber stands. This species can be found in early successional units of both hills and lowlands and are common in both agricultural and pastoral lands such as fields of alfalfa (Medicago sativa), wheats (Triticum), or oats (Avena sativa), or filbert orchards, weedy pastures, and lands damaged by clearing. Their habitats in this valley range in elevation from 120 to 125m above sea level. They avoid wetlands and poorly drained grasslands. (Bailey, 1936; Cassola, 2016; Wight, 1918; Wight, 1922)

Nesting cavities can be entered by two or more openings, connecting usually with the deeper underground passageways. On low grasslands, the nests are often less than 0.30 m beneath the surface whereas on better-drained slopes, these pocket gophers nest at a depth of 0.61 to 0.91 m. The maximum depth of these gophers' burrows may be as great as 1.5 to 1.8 m. The diameter of a burrow is about 7.6 cm but varies with the body size of the gophers. Their burrow systems are often quite active, with portions regularly sealed off and new areas quarried. A single burrow system could hold up to 180 m of tunnels. ("Habits and economic status of the pocket gophers", 1931; "Pocket gophers", 1994; Cassola, 2016)

  • Range elevation
    125 (high) m
    410.10 (high) ft
  • Average elevation
    120 m
    393.70 ft

Physical Description

Camas pocket gophers have small, weak eyes that rarely open, small ears, short legs, powerfully- built shoulders, slim hips, and a nearly naked tail that can be from 40 to 95 mm long. They have vibrissae (whiskers), as well. They have fur-lined cheek pouches and reach total lengths of 228.6 to 330.2 mm and weights of 633 g. They are the largest pocket gopher in their genus. Their fingers and palms are equipped with fringes of stiff bristles and the hind feet usually exceed 40 mm in males and 38 mm in females. Their middle toes are the longest and the claws on their forefeet are longer than those on their hind feet. Their front claws are the smallest in the genus and relatively weak, instead relying on their large chisel-like incisors for digging in soil. Both the upper and lower incisors are white-tipped due to abrasion of the yellow surface enamel and are fairly narrow. The incisors also protrude with the lips closing behind them. A groove (sulcus) on the median edge of each incisor is lacking, though present in other members of the genus. Their dental formula is i 1/1, c 0/0, p 1/1, m 3/3, with a total of 20 teeth. (Bailey, 1936; Nowak, 1999; Verts and Carraway, 1987; Verts, 1999; Wight, 1918; Wight, 1922)

For camas pocket gophers, it is difficult to determine sex by external characteristics. Males lack a protruding penis and the testes are generally internal. Non-reproductive adult female pocket gophers have the pelage and external characteristics of immature gophers. Size can sometimes determine sex, as males are typically 10% heavier and 3-4% greater in total length than females. (Baker, et al., 2003)

Appearance of camas pocket gophers vary greatly not just with differences in age, sex, and season. The dorsum color can range from a very dark sooty brown to a bright reddish brown and the male usually showing a more grizzled appearance. The venter is lead-colored except for an irregularly-shaped white patch on the throat. The chin and with rare exceptions, the anal patch and markings on the feet are also white while the nose and ears are dark, or blackish. The pelage varies upon season with the winter pelage being long and furry and the summer pelage being short and coarse. (Verts and Carraway, 1987; Wight, 1918; Wight, 1922)

  • Sexual Dimorphism
  • male larger
  • Range mass
    633 (high) g
    22.31 (high) oz
  • Range length
    228.6 to 330.2 mm
    9.00 to 13.00 in

Reproduction

Before mating season, in the spring, both female and male camas pocket gophers do not associate with one another. If they do come in contact with one another, The males fight aggressively with the females, but when given the opportunity, the females run away. From late February through March, certain mates will live together during the breeding period. During the mating process, males leave their burrows to find and mate in the females’ burrows. After mating, the females leave their burrows to find another place to protect themselves and their young from other gophers and possible threats before giving birth. Males play no further part in rearing the young. Male camas pocket gophers are serial monogamists. This means that they mate in series throughout their lifetime, being committed to one female for one breeding period until the females move away. Female camas pocket gophers are also monogamous, but no research tells if they mate in series. ("Pocket gophers", 1994; Baker, et al., 2003; Wight, 1918; Wight, 1930)

Camas pocket gophers’ breeding season lasts from early March to early July. They give birth to young between the first of April and the beginning of the summer season, extending as late as July. The gestation period lasts from 18 to 19 days. Females generally produce four to nine young in a litter, averaging 4.2. At birth, the young appear shapeless, weighing about 6.1 g and averaging 50 mm long. They are blind and lack hair, pockets, and teeth. Growth is rapid, and by two weeks the young have begun to develop thin hair that has a brownish appearance. By three weeks, they can crawl and consume solid food, such as succulents, using their tiny paws. By four weeks, they develop pockets, and by five weeks they can open their eyes. By six weeks, the young weigh 85.05 g and are nearly 177.8 mm long. At this time, they have learned to grind and chatter their teeth like grown adults. This begins the weaning period, which is determined by their mothers once they seem mature. After they are kicked out of their mother’s burrow, the juveniles search for their own burrows and live in solitude. They reach sexual maturity a year after they are born. (Verts and Carraway, 1987; Wight, 1918; Wight, 1922; Wight, 1930)

  • Breeding interval
    Camas pocket gophers breed every spring season
  • Breeding season
    March to July
  • Range number of offspring
    4 to 9
  • Average number of offspring
    4.2
  • Range gestation period
    18 to 19 days
  • Range weaning age
    6 (high) weeks
  • Range time to independence
    6 (high) weeks
  • Range age at sexual or reproductive maturity (female)
    1 (high) years
  • Range age at sexual or reproductive maturity (male)
    1 (high) years

Once the gestation period begins, the mothers leave their initial burrows and seek protection elsewhere. Fathers have no ability to invest in the young after mating, because the mothers leave them. Female camas pocket gophers rarely leave their burrows until the young are weaned to avoid potential threats. After birth, the young are covered in the nest to make up for their lack of hair and inability to thermoregulate sufficiently. Young camas pocket gophers depend on their mothers for warmth. During feeding/suckling time, mothers will place their heads far back under their bodies, spread their hind legs far apart, and raise their abdomen. At this time, the young lie on their backs, often resting upon their mothers’ throat and chin to be hidden away. If the mothers feel threatened, they’ll drag their young from the nest and complete the feeding process when protected from all threats. By the time the young are three weeks old, they begin to consume the food their mothers have placed beneath the nests for them. At the age of weaning, the mothers kick them out and leave them to fend for themselves. ("Habits and economic status of the pocket gophers", 1931; Bailey, 1936; Nistler, et al., 1993; Verts and Carraway, 1987; Wight, 1918; Wight, 1930)

  • Parental Investment
  • female parental care
  • pre-fertilization
    • provisioning
    • protecting
      • male
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

There is little research on the longevity of camas pocket gophers. A similar species, Botta's pocket gophers (Thomomys bottae), live up to 4.8 years in the wild and up to 6.1 years in captivity. It is assumed that a similar lifespan applies for camas pocket gophers. However, camas pocket gophers are not often kept in captivity. (Howard and Childs, 1959; Weigl, 2005)

Behavior

Camas pocket gophers are specialized in burrowing activity. While digging, they almost turn completely upside down to use their teeth to break up the large chunks of soil. They then paw the soil back underneath their stomach with their front feet and give one last kick to the soil with their hind feet. These large packs of soil that are loosened by their teeth and claws are pushed out the entrance with a side to side motion to one of the inclined lateral tunnels to form a fan-shaped mound. These tunnels are usually sealed up with the soil mounds well packed in place, except for when the soils are wet and an opening is left at the top of the burrow. These mounds that have chimney structures are thought to be made for increased ventilation and tunnel drying. Their burrowing activity is largely fossorial despite evidence of some predatorial advantages that suggest some surface activity. (Baker, et al., 2003; Verts and Carraway, 1987; Wight, 1918; Wight, 1922)

Most of the activity is carried out underground. Camas pocket gophers are both diurnal and nocturnal. In soft, moist soil, camas pocket gophers can dig at a rate of 1828.80 mm an hour while hard baked soil requires more time and skill, averaging a rate of 457.2 mm an hour. Tunnel development continues as their main activity throughout their lifetimes. Underground burrow system building is estimated to require 360-3400 times the energy of moving across the surface. Because this activity increases from spring through summer and into fall, it is thought to be important for increased survival and food availability. ("Pocket gophers", 1994; Baker, et al., 2003; Wight, 1918; Wight, 1922)

Camas pocket gophers are known as one of the most vicious animals, renowned for their size and fighting ability. In captivity, they may become tame but still have little tolerance for conspecifics. In their natural habitat, they are solitary, constantly sealing off their interconnected burrows from each other except during mating season. An imperative behavioral feature of camas pocket gophers is their response to any motion that opens their burrows. If they come across an opening, they will immediately seal the opening up by pushing dirt to the surface and packing the burrow system some distance below the surface. This activity is thought to be adaptive in protecting against threats by creating a wall of soil to block intruders. When they come across predators in their homes, such as weasels, snakes, and other threats, they generally react by getting into a threatening posture with their mouth open, making panting sounds, and raising the front of their bodies slightly with their claws extended frontward. This behavior usually chases away other gophers encountered in their runways. If the intruder is a snake, they fight aggressively with many strikes to the predator using their sharp incisors and claws. If needed, camas pocket gophers will run away. ("Pocket gophers", 1994; Baker, et al., 2003; Verts and Carraway, 1987)

Home Range

Most of daily lives for camas pocket gophers are within their burrow systems. The burrow system size on average for camas pocket gophers rarely exceeds 240 m in total length. In diameter, they range from 51 to 127 mm and from 0.08-0.91 m below surface. Home ranges and territories have not been quantified in the literature. (Verts and Carraway, 1987)

Communication and Perception

The most common sounds of camas pocket gophers are made by the chattering of their teeth. They can make noise by moving their teeth in a straight up and down motion or grinding them with a more lateral motion. The first sound is largely understood as a sign of discomfort and is made when they appear aggressive and challenging toward a threat. The lateral grinding sound can be heard when they are alone. They make a cry of pain when injured. Crooning sounds and purrs are heard when a male and female wish to mate. Mothers communicate with their young and the young respond with a chirping sound. (Wight, 1918)

Some observations suggest that the gophers have a form of chemical communication and perception. There is a white, milky fluid that is secreted over the eye upon some emotional stimulation. This substance secretes when the animal is in a state of discomfort. These gophers also have poor sense of direction and when let out of captivity have trouble finding their burrow again. (Wight, 1918)

Food Habits

The diet of camas pocket gophers consists of a wide range of plants, fruits and other vegetation but they are most commonly associated with their consumption of bulbs from camas (Camassia) which grow abundantly in their valley. While that may be their most common food, the camas pocket gopher forages on roots, bulbs, and tubers obtained opportunistically while extending their tunnels. Roots and leaves of many plants such as cat’s ear (Hypochaeris radicata) as well as the bark from the woody roots of bushes and trees are often consumed so much as to obliterate the plants. The roots of apples (Malus pumila) and pear trees (Pyrus) are the most commonly consumed but many other fruit or orchard trees such as peach trees (Prunus persica), nut trees, and walnut roots (Juglans) are also disturbed by the gophers. When the animal comes to the surface, they usually stuff their cheek pouches with vegetation gathered near the opening of their burrow, mostly clover (Trifolium), alfalfa (Medicago sativa), thistles, and succulents. They also grab grasses, grains, and a variety of crops and vegetables such as carrots (Daucus carota) and plantain (g. Plantago) as they come upon them. Many observations have detected these animals of smelling like wild onion (Allium) suggesting that, too, was frequently eaten. (Bailey, 1936; Verts and Carraway, 1987; Wight, 1918)

The food of camas pocket gophers is taken to a good degree from below, the root being cut off first from beneath the ground and taken back to their burrows. Food such as parsnips and carrots have been retrieved in this way. Dandelions (Taraxacum) are generally collected and placed in their burrows, too. The roots are stored in the caches and the leaves are put beneath the animal’s nest. Several observations, show that they will take food from about their open burrows, reach out, cut the food off and pull it back into the hole. ("Habits and economic status of the pocket gophers", 1931; Wight, 1918)

The underground chambers that are excavated for the sole purpose of storing food vary in size according to the resources within reach and with seasonal demands. The storage areas are often near the surface in these underground chambers which connect with the feeding runs. This arrangement, in turn, streamlines the transportation of resources in the harvest season. ("Habits and economic status of the pocket gophers", 1931; Wight, 1918)

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

Predation

Pocket gophers in this genus are mainly prey to badgers (Taxidea taxus), coyotes (Canis latrans), weasels, and some snakes. They are most often preyed on during times of feeding, at or near the surface, or when moving soil and debris to the surface. During this time, they are vulnerable to other animals such as hawks, owls, foxes, bobcats (Lynx rufus), spotted skunks (Spilogale gracillis), and house cats (Felis catus), as well as coyotes. The main owl species that prey on camas pocket gophers are great-horned owls (Bubo virginianus) and barn owls (Tyto alba). Birds appear to be the most capable of capturing pocket gophers. Camas pocket gophers spend most of their lives in solitude, and because of this they are less susceptible to predation and have an increased likelihood of surviving past reproductive age.

When they come across predators in their homes, such as weasels, snakes, and other threats, they generally react by getting into a threatening posture with their mouth open, making panting sounds, and raising the front of their bodies slightly with their claws extended frontward. This behavior usually chases away other gophers encountered in their runways. If the intruder is a snake, they fight aggressively with many strikes to the predator using their sharp incisors and claws. If needed, camas pocket gophers will run away. ("Pocket gophers", 1994; Baker, et al., 2003)

Ecosystem Roles

Most of the activities that camas pocket gophers do daily, such as burrowing, mound production, and tunneling, harshly affect soil arrangement. Their burrowing activity often leaves plants buried or removed from the surface, and soil tends to erode when left at the surface. When vegetation is scarce, there is a presence of more sand particles in the mounds left at the surface that can also lead to increased wind and water erosion. These mounds at the surface differ in nutrient content from surrounding microhabitats and lead to an increase in plant biodiversity. Alternately, camas pocket gophers can also harm an area by their feeding habits. They can greatly reduce plant biomass in areas where disturbance is naturally uncommon. Their feeding runways are centered around the root sectors of plants, thus extending the likelihood that root exposure inside the tunnels may increase root withering. In the Thomomys genus alone, pocket gophers can remove as much as 30% of the subterranean net primary productivity.

Camas pocket gophers help soil in many ways, such as increasing soil aeration, water filtration, and soil formation. The increase in soil aeration and water filtration results in the decrease of soil compaction and runoff. Camas pocket gophers increase soil formation by moving subsoil substances to the surface. They also increase soil fertility by adding organic material such as their buried vegetation and fecal wastes.

Camas pocket gophers are hosts to some parasitic and commensal species. Parasitic or commensal species known to camas pocket gophers are the mites (Androlaelaps fahrenholzi, Echinonyssus femuralis), and chewing louse (Geomydoecus oregonus), which are all ectoparasites. Other species that use camas pocket gophers as hosts are nematodes (Trichuris fossor, Ransomus rodentorum) and cestode species (Hymenolepis horrida). Camas pocket gophers are also mutualists in their environment with the gray-tailed voles (Microtus canicaudus) that use their tunnels. ("Pocket gophers", 1994; Baker, et al., 2003; Verts and Carraway, 1987)

Mutualist Species
Commensal/Parasitic Species
  • nematode (Trichuris fossor)
  • nematode (Ransomus rodentorum)
  • mite (Androlaelaps fahrenholzi)
  • mite (Echinonyssus femuralis)
  • chewing louse (Geomydoecus oregonus)
  • cestode (Hymenolepis horrida)

Economic Importance for Humans: Positive

Camas pocket gophers cultivate soil, bury vegetation with their chunks of soil, and improve the soil for the use of humans. The soil mounds left at the surface are bare patches, which may differ in nutrient content from intermound areas, allow for the exchange of gases and the movement of water through soils with greater ability. These bare patches are areas where succession must start over, increasing the diversity of plants in the area of disturbance. (Bailey, 1936; Baker, et al., 2003)

Economic Importance for Humans: Negative

Camas pocket gophers, like other gophers, are considered a known financial burden to humans. These gophers can threaten livestock and crops. The density of pocket gophers in an area can negatively affect the productivity of crops due to burrowing activity and feeding on plants. Their feeding activity causes great damage to machinery, irrigation systems, and buried electrical and telephone cables. The amount of damage caused by pocket gophers, in general, costs over a million dollars to fix yearly.

In smaller, surrounded pastures where clovers and grasses are mixed, camas pocket gophers can often be troubling. They cover up parts of the surface with their soil mounds which interfere with harvesting. Because of scarcity, grasslands are often so disturbed that they have the appearance of being cultivated. This is because food isn't nearly as available here as it is in alfalfa (Medicago sativa) and clover (Trifolium) fields, so camas pocket gophers tend to dig more extensively in search of grassier foods. Agriculturalists must clear these lands of the pocket gophers in order to be profitably handled for the production of hay. Camas pocket gophers also get into farmers’ storage areas and take away agricultural products. The extent of damage caused by these pocket gophers is not detectable until it has already caused economic harm. It is because of these activities that humans have been studying extensive ways to control camas pocket gophers. ("Pocket gophers", 1994; Bailey, 1936; Baker, et al., 2003)

  • Negative Impacts
  • crop pest

Conservation Status

According to the IUCN Red List, this species is listed as Least Concern. Camas pocket gophers’ range and populations are not currently declining. They are adapted to human disturbance in their habitat. Locally, in orchards and fields, they are viewed as crop pests and are lethally removed by poisoning and trapping. Other sources, such as the US Federal List, CITES, and State of Michigan List, have no special status for this species. There are no known conservation efforts for this species. Indeed, most efforts focus on eradicating nuisance populations. (Cassola, 2016)

Contributors

Tiffany Parker (author), Radford University, Alex Atwood (editor), Radford University, Layne DiBuono (editor), Radford University, Lindsey Lee (editor), Radford University, Karen Powers (editor), Radford University, Joshua Turner (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

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

agricultural

living in landscapes dominated by human agriculture.

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

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

female parental care

parental care is carried out by females

folivore

an animal that mainly eats leaves.

fossorial

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

frugivore

an animal that mainly eats fruit

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).

monogamous

Having one mate at a time.

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.

nocturnal

active during the night

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

soil aeration

digs and breaks up soil so air and water can get in

solitary

lives alone

stores or caches food

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

suburban

living in residential areas on the outskirts of large cities or towns.

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.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

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

USDA Technical Bulletin (Scheffer, T.H.). Habits and economic status of the pocket gophers. 224. Washington, D.C.: United States Department of Agriculture. 1931.

Wildlife Damage Management, Internet Center for Damage (Case, R.M. and Jasch, B. A.). Pocket gophers. 13. Lincoln, Nebraska: University of Nebraska. 1994.

Bailey, V. 1936. The mammals and life zones of Oregon. North American Fauna, 55: 1-348.

Baker, R., R. Bradley, L. McAliley, Jr. 2003. Pocket gophers. Pp. 276-284 in G Feldhamer, B Thompson, J Chapman, eds. Wild Mammals of North America: Biology, Management, and Conservation. Baltimore, Maryland: The Johns Hopkins University Press.

Carraway, L., P. Kennedy. 1993. Genetic variation in thomomys bulbivorus, an endemic to the Willamette Valley, Oregon. Journal of Mammalogy, 74/4: 952-962.

Cassola, F. 2016. "Thomomys bulbivorus" (On-line). The IUCN Red List of Threatened Species 2016: e.T42594A22216513. Accessed January 31, 2018 at http://dx.doi.org/10.2305/IUCN.UK.2016-2.RLTS.T42594A22216513.en.

Hill, J. 1935. The retractor muscle of the pouch in the Geomyidae. Science, New Series, 81/2093: 160.

Howard, , Childs. 1959. Ecology of pocket gophers with emphasis on Thomomys bottae mewa. Hilgardia, 29: 277-358.

Nistler, D., B. Verts, L. Carraway. 1993. Aging techniques, juvenile breeding, and body mass in thomomys bulbivorus. Northwestern Naturalist, 74/1: 25-28.

Nowak, R. 1999. Walker's mammals of the world. Baltimore and London: The Johns Hopkins University Press.

Schramm, P. 1961. Copulation and gestation in the pocket gopher. Journal of Mammology, 42/2: 167-170.

Verts, B., L. Carraway. 1991. Summer breeding and fecundity in the camas pocket gopher, thomomys bulbivorus. Northwestern Naturalist, 72/2: 61-65.

Verts, B., L. Carraway. 1987. Thomomys bulbivorus. Mammalian Species, 273: 1-4.

Verts, B. 1999. Suculi in upper incisors of Thomomys bulbivorus. Northwestern Naturalist, 80/1: 30-32.

Weigl, R. 2005. Longevity of Mammals in Captivity; from the Living Collections of the World. Stuttgart, Germany: Kleine Sencken-Reihe 48.

Wight, H. 1918. The Life-history and Control of the Pocket Gopher in the Willamette Valley. Corvallis, OR: Oregon Agricultural Experiment Station.

Wight, H. 1930. Breeding habits and economic relations of the Dalles pocket gopher. Journal of Mammalogy, 11/1: 40-48.

Wight, H. 1922. The Willamette Valley gopher. The Murrelet, 3/3: 6-8.