The Gambian pouch rat, Cricetomys gambianus, also known as the African Giant Pouch rat, is a nocturnal pouched rat native to Africa, and an invasive alien species in Florida. It is the largest rat in the world.
Characteristics
Gambian pouch rats can grow to be as big as a raccoon and can weigh up to 4 kg. They have very poor eyesight and so depend on their senses of smell and hearing. Their name comes from the large, hamster-like pouches in their cheeks. They are not true rats (subfamily Murinae), but are part of a uniquely African radiation of muroid rodents.
In their native Africa, these rats live in colonies of up to twenty strong, usually in forests and thickets, but also commonly in termite mounds. They are completely omnivorous, feeding on vegetables, insects, crabs, snails, and other items, but apparently preferring palm fruits and palm kernels.
Unlike domestic rats, they have cheek pouches like a hamster. These cheek pouches allow them to gather up several kilograms of nuts per night for storage underground. They have been known to stuff their pouches so full of date palm nuts so as to be hardly able to squeeze through the entrance of their burrows. The burrows consist of a long passage with side alleys and several chambers, one for sleeping and the others for storage.
Gambian pouch rats reach sexual maturity at 5-7 months of age. They have up to four litters every nine months with up to six offspring in each litter.
Male pouch rats are territorial and tend to be aggressive when they encounter one another, otherwise these rodents are extremely friendly and have become popular as exotic pets. They are intelligent, social and can be very gentle if handled from an early age.
In Africa, they are routinely eaten as bushmeat. They (and other mammals) are referred to by the pidgin name of “beef”.
Problems with the pouch rat
Currently these rats have been an invasive species on Grassy Key in the Florida Keys. Perry et al. (2006) confirmed that animals found on the island are, in fact, representative of a breeding population and are not isolated escapees. It is unknown how the rat was released to the wild, and there is fear that if the rats reach Key Largo they could invade the Everglades and cause great ecological damage. Peterson et al. (2006) determined through computer modeling that C. gambianus (and, to a lesser degree C. emini) has strong potential to be a successful invasive across much of the mainland USA, particularly the southeast. Biologists say it would compete for food with native species, carry diseases, and damage the bird population by eating their eggs.
This outsized African rodent is also believed to be responsible for the current outbreak of monkeypox in the United States. In 2003, the United States’ Centers for Disease Control and Prevention and the Food and Drug Administration issued an order preventing the importation of the rodents following the first reported outbreak of monkeypox. Several African species are believed to carry the disease.
Pouch rats as mine-sniffers
A Belgian company has begun training Giant Pouch Rats to sniff out mines. Due to their excellent sense of smell and tractable personality the Giant Pouch Rat has excelled in this application. They are clicker trained from an early age to associate the smell of explosives with a food reward, usually banana or a peanut. In the field, the rat wears a harness connected to a rope suspended between two handlers. Multiple rats sweep up and down an area about the size of racquetball court one at a time and areas that the rats signal to (usually by stopping and scratching) are noted on a grid of the area. When an area has been thoroughly swept by the rats a team with metal detectors goes in and detonates all mines in the area.
Using Giant Pouch Rats in place of dogs has several advantages. The rats are indigenous to Africa where they are used and thus are well suited to the climate and are resistant to many endemic diseases. They are also widely available and inexpensive to procure. Training time is much shorter for rats than dogs and fewer resources are needed to raise a rat to adulthood, and Giant Pouch Rats have a relatively long life span.
In the field the rat’s relatively small size means that it rarely detonates mines by walking over them. Both rat and rat handler teams are therefore safer than are dogs and dog handler teams. Furthermore, large areas can be swept by multiple rats for multiple bombs before a detonation team goes in to explode the detected bombs. This cuts down on the time needed to search a particular area, since with dogs each land mine must be detonated as it is detected, to avoid the greater danger of search dogs detonating land mines. The rat’s small size also means that many rats can be easily transported to and from field sites.
As with the use of dogs land mines that have been manufactured to be completely sealed cannot be detected. These mines must be detected with metal detectors, since both dogs and rats use their sense of smell to detect trace amounts of explosive that leak from land mines.
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