Camas rat, Willamette valley gopher
The camas pocket gopher (Thomomys bulbivorus ), also known as the camas rat or Willamette Valley gopher, is a rodent, the largest member in the genus Thomomys, of the family Geomyidae. First described in 1829, it is endemic to the Willamette Valley of northwestern Oregon in the United States. The herbivorous gopher forages for vegetable and plant matter, which it collects in large, fur-lined, external cheek pouches. Surplus food is hoarded in an extensive system of tunnels. The dull-brown-to-lead-gray coat changes color and texture over the year. The mammal's characteristically large, protuberant incisors are well adapted for use in tunnel construction, particularly in the hard clay soils of the Willamette Valley. The gophers make chattering sounds with their teeth; males and females make purring (or crooning) sounds when they are together, and the young make twittering sounds. Born toothless, blind and hairless, the young grow rapidly before being weaned at about six weeks of age.
Although the camas pocket gopher is fiercely defensive when cornered, it may become tame in captivity. While population trends are generally stable, threats to the species' survival include urbanization, habitat conversion for agricultural use and active attempts at eradication with trapping and poisons. It is prey for raptors and carnivorous mammals, and host to several parasitic arthropods and worms. Scientists believe that the gopher's evolutionary history was disrupted when the Missoula Floods washed over the Willamette Valley at the end of the last ice age. The floods almost completely inundated its geographic range, which may have caused a genetic bottleneck as survivors repopulated the region after the waters receded.
The camas pocket gopher is, by a small margin, the largest member of its genus (Thomomys ). The fur is a dull brown above and dark, leaden gray beneath. There are often patches of white on the chin, throat and around the anus, and it has blackish ear and nose markings. The external ear is a thickened rim of tissue. During the summer, the gopher's coat is short and coarse; winter pelage is longer and furrier. The coat of the young is similar to the adult summer coat, but with more sparsely distributed fur; the abdominal skin may be visible.
Like other gophers, it has small eyes and ears and a nearly hairless tail. Its shoulders are broader than its hips. It is pentadactyl, with five claws on each foot. The claws on its forefeet are longer than those on its hind feet, and its middle claws are longest. The front claws of the camas pocket gopher are short and weak relative to its size. It employs plantigrade locomotion. The male is larger than the female, measuring an average 300 mm (12 in) in length. A large male weighs about 500 g (18 oz). One male specimen was 321 mm (12.6 in) long and weighed 633.8 g (22.36 oz). Females are about 271 mm (10.7 in) long. The tail measures 90 mm (3.5 in) in the male and 81 mm (3.2 in) in the female. An adult male's hind feet measure 40–43 mm (1.6–1.7 in), and an average female's hind feet measure 39 mm (1.5 in). There are four mammary glands: two in the inguinal region and two in the pectoral region, each supplying a pair of nipples. Morphologically, it most closely resembles Botta's pocket gopher; differentiation can be made based on the concavity of the inner surface of the pterygoids, small claws, more uniform fur coloring and exoccipital groove of the camas pocket gopher.
The camas pocket gopher is found in the Willamette Valley and the drainage areas of the Yamhill River and other tributaries of the Willamette River. Its range extends north from Eugene to Portland and Forest Grove and west to Grand Ronde. A 1920 report of a Pleistocene fossil in Fort Rock, Oregon has been questioned, since it is far outside the species' current geographic range; as of 1987, the specimen could not be located for further evaluation.
The clay-rich Willamette Valley soils are hard in the dry season, and the gopher's protuberant incisors are well adapted to these conditions. Adequate soil drainage and suitable plant food are essential components of the gopher's ideal habitat. Not typically found in wetland areas (where its tunnels would flood), the species is found in seral communities of grasses and shrubs. They are also established in agricultural fields in the Willamette Valley, including fields of alfalfa, wheat and oats. The species has also been found in areas of ecological disturbance with similar terrain features.
On a geologic timescale, the Willamette Valley has been the site of massive floods. During the late Wisconsin glaciation, a series of floods (known as the Missoula or Bretz Floods) occurred. The last flood in the series, a massive flood with an estimated 1,693 km3 (406 cu mi) of water flowing at a rate of 42 km3 per hour (412 million ft3 per second) over a 40-hour period, occurred about 13,000 years ago. The flood filled the Willamette Valley to a depth of about 122 m (400 ft), in a near-perfect overlay of the camas pocket gopher's range. Although the species has been collected above this elevation, such finds are uncommon. A temporary lake, Lake Allison, formed. Although it is assumed that the gopher lived in the valley before the flood, no fossils have been recovered. The Chehalem Mountains, with a peak elevation of 497 m (1,631 ft), probably provided refuge for survivor populations and survivors would have repopulated in isolated pockets when the waters receded. Before and since the floods, the mountains are thought to have limited gene flow between populations. The relatively narrow, sluggish Willamette River does not appear to obstruct genetic flow in gopher populations.
The camas pocket gopher is a mostly solitary herbivore which is active throughout the year and does not hibernate.The gopher spends most of its time excavating tunnels in search of food, and the hard clay soils of the Willamette Valley pose a challenge. Although the gopher's front claws are too weak to dig through the clay (particularly during dry seasons), its large incisors and strongly protuberant orientation are well-adapted for this purpose. Tunnel systems constructed by the camas pocket gopher can be complex, with some tunnels exceeding 240 m (260 yd) in length. About 90 mm (3.5 in) in diameter, the tunnels are up to 0.91 m (3.0 ft) deep. When soils are damp the gopher constructs ventilation ducts or chimney mounds (possibly unique to the species), to increase ventilation. The chimney mounds rise vertically 15–25 cm (6–10 in), are open at the top and are thought to ventilate the burrows in accordance with Bernoulli's principle. It is not known if adjacent gopher burrowing systems interconnect. Reports differ about whether or not the ranges of the camas pocket gopher and the Mazama pocket gopher overlap; if so, this refutes the previous belief that Oregon gopher ranges do not overlap.
Although the species is primarily fossorial, it occasionally gathers food near the entrance of a tunnel. Dandelions seem to be its favorite food, and are also used as nesting material. During breeding season males will enter the tunnels of females, and males and females may make purring (or cooing) sounds when they are together. Mothers seem to comfort the young by softly vocalizing, with the young twittering in response.
The camas pocket gopher may behave aggressively when on the defensive, with mammalogist Vernon Orlando Bailey describing the species as "morose and savage." However, it may be easily tamed in captivity; the female is more readily tamed than the male. Another small rodent endemic to the Willamette Valley, the gray-tailed vole (Microtus canicaudus ), also uses camas pocket gopher tunnels. Other mammals sharing the range of the camas pocket gopher (and, possibly, its tunnels) include the vagrant shrew, Townsend's mole, the brush rabbit, the eastern cottontail rabbit, Townsend's chipmunk, the California ground squirrel, the dusky-footed woodrat, the North American deermouse, the creeping vole, Townsend's vole, the Pacific jumping mouse, the long-tailed weasel and the striped skunk.
Varying onset times and duration of the camas pocket gopher breeding season have been reported. Early reports suggested an early-April onset, with the season extending through June. Other reports cited "evidently pregnant" females seen in late March. In heavily irrigated areas the breeding season may be longer, extending into early September. About four young are born in a litter, although litters as large as nine have been reported. The blind, hairless, toothless offspring weigh about 6.1 g (0.22 oz) and are 50 mm (2.0 in) in length. During their first six weeks they will begin to crawl, develop cheek pouches, open their eyes and wean from milk to solid food. The young then weigh about 86 g (3.0 oz) and measure 164 mm (6.5 in) in length. At weeks 8, 10 and 17 they will weigh 101 g (3.6 oz), 160 g (5.6 oz) and 167 g (5.9 oz). Some reports indicate that more than one litter may be born in a season. Sexual maturity probably develops by the following year's breeding season. Although males are fully grown by that time, females may continue to increase in size.
There was little data as of 1998 on the longevity and mortality of the camas pocket gopher. It is presumably prey for carnivorous mammals, and its bones have been identified in regurgitated pellets of raptors such as the great horned owl. Parasites include mites, lice, fleas, roundworms and flatworms. The species' tougher skin may protect it from some fleas known to infest Botta's pocket gopher and the Mazama pocket gopher. Mites known to parasitize the camas pocket gopher include Androlaelaps geomys and Echinonyssus femuralis. Some authorities report Androlaelaps fahrenholzi as another parasitic mite, but a later publication did not report it. The chewing louse Geomydoecus oregonus has also been reported.
Two parasitic worms first discovered in the gastrointestinal tract of camas pocket gophers are the nematode Heligmosomoides thomomyos and the cestode Hymenolepis tualatinensis. Other worms include two nematodes and the cestode Hymenolepis horrida.
Citing concerns of urbanization, habitat loss and active attempts at eradication, NatureServe assessed in 2014 the camas pocket gophers' conservation status as vulnerable. The conservation status of the camas pocket gopher is classified as "least concern" by the IUCN (International Union for Conservation of Nature) Species Programme, with a stable population trend. The IUCN notes that the gopher is common in its range; studies indicate that populations can recover rapidly after traps are removed from an area, and the species may adapt well to environmental changes.
The IUCN and others express concern about degradation of the species' habitat due to urbanization and agricultural expansion. The total area occupied by the camas pocket gopher is less than 20,000 km2 (7,700 sq mi). This area, the Willamette Valley, contains 70 percent of Oregon's human population. Although this range probably contains a few protected areas, many preserves in the valley are primarily waterfowl protection for hunters. Wetland areas are not suited to the camas pocket gopher, since tunnels are flood-prone. In areas better suited to the gopher (disturbed habitats and pastoral farmland), it may be considered a pest and subject to eradication by poisoning and trapping.
