Sunday, 13 June 2010

Rodents of Bristol 1: Hopping to it

To kick of a new series on Bristol Zoos rodents, I will begin with one of the cuter rodents we have here – Merriam’s Kangaroo Rat Dipodomys merriami. We have some on show in Twilight World and their characteristic method of locomotion (shared with several other desert rodents) always draws a crowd. This dry land rodent is found throughout the south western North America from California to Mexico. It gets its name from the hopping method of locomotion it uses – they can jump up to 1m in any direction, which comes in handy when escaping from rattlesnakes, one of their main predators.

Like many rodents it is solitary, living in burrows which usually have entrances at the base of shrubs. The only time several animals share a burrow system is when a female has young – up to four pups three times a year from February to May.

In a desert food is scarce, and kangaroo rats are famous for their hoards. Most of the diet is seeds of grasses and desert plants, which they carry back to their hoards in cheek pouches. They also eat some insects, especially during the winter months when seeds have mostly been collected and they are living off their hoards. They do not need to drink, as they can produce metabolic water from the process of digestion, and their kidneys are extremely efficient in retaining water.

Merriam’s kangaroo rat is not endangered, as it has a wide range and appears to be quite adaptable in its habitat requirements. Other species however have small ranges or more exacting requirements, such as being confined to particular dune systems, and some of them are threatened. For example, the Giant Kangaroo Rat Dipodomys ingens from the San Joaquin valley in California, which is 15cm long excluding the equally long tail, is classed as threatened.

All told there are over 20 species in Dipodomys, which despite its appearance is not related to the Old World Jerboas, which have a very similar lifestyle. The kangaroo rats are most closely related to the pocket mice and kangaroo mice in the Heteromyidae, a family endemic to the Americas which appears to have originated in North America and spread into northern South America in the last few million years.

Not many zoos keep kangaroo rats – ISIS lists only 61 Merriam’s kangaroo rat worldwide, with 39 in Europe. Bristol has bred them several times (we currently hold 12 individuals) and some are on show in Twilight World. As an experiment one has been kept with Chuckwallas and Collared Lizards in the reptile house. It did OK and did not interfere with the reptiles, but as might be expected was seldom visible when the public were around – they are very reluctant to appear above ground in daylight, and even on moonlit nights will tend to stay in their burrows.

Despite the huge diversity of rodents, a very small selection of species is on show in zoos, as they are mostly nocturnal and many species are hard to tell apart by non-specialists. Their husbandry is mostly straight forward, with a diet of seed mix plus some mealworms or crickets sufficing for most desert rodents. The other main factor is their territoriality – with the solitary species males and females should only be placed together for mating and separated immediately afterwards. Providing sufficient space is available, pups should be raised without too many problems.

In fact, one species, that is so rare in the wild that for many years it was believed to be extinct, has become a popular pet. It is of course the Syrian or Golden hamster, Mesocricetus auratus. In the wild the Syrian hamster is found only on the borders of Syria and Turkey, and may have a population as low as 2,500 adults – extremely low for a small rodent. The main threat is persecution as a crop pest and loss of habitat.

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