Click here for photographs.

Introduction

The Jaculus genus contains two subgenera and a total of five species. This text will concentrate on J. jaculus and J. orientalis, the Lesser and Greater jerboas respectively. While they remain rare their scientific names are generally used to avoid confusion. They are sometimes misleadingly refereed to as 'Kangaroo Rats/Mice' or 'Desert Rats'. As with Jirds their name is often mis-spelt 'Gerboa'.

In the wild J. jaculus covers the whole of Northern Africa; Mauritania to Morocco and Egypt. J. orientalis ranges from Morocco through Israel. Here they choose the most inhospitable areas of the Earth to inhabit.

Both species construct similar burrows; extending about 3-4m to a depth of 1-2m, it includes sleeping quarters and escape exits. The burrows of J. jaculus spiral anticlockwise. In the case of J. orientalis the burrow includes a food storage chamber. Nesting material will contain shredded vegetation and camel hair.

These burrows provide accommodation all seasons. They will cover or block the entrances during the day and night.

J. jaculus the smallest member of the genus has a weight of approximately 55g. While the largest of the genus, J. orientalis, has a weight of 134g, a body length of around 147.5mm, a tail of around 220mm, and hind feet of 75mm.

You can expect both species to live to a maximum of 5-6 years.

Specialisation for desert life

The fore-feet of both species are generally a fourth of the length of hind feet. The tail is tipped with a bush of dark/black fur which, in turn is tipped with white. This is thought to a distraction to predators in a chase or in the unlikely event they are cornered.

Both species have three toes on each hind foot with a cushion and fringe of hair; this hair has the affect of a snowshoe on snow (giving a larger surface area and better grip) but also provides a buffer between the hot desert sands and the delicate sole of the foot.

J. jaculus is able to jump somewhere in the region of one metre high and three in length in a single bound, with the ability to change direction with each bounce. They are able to run bipedally (on two feet) turning right angles suddenly. The tail is used for balance and acts as a rudder.

Their tails are truly versatile tools, not only is it used as described above and as a prop when still but is likely to help control their temperature. Tiny blood vessels are expanded or contracted to dissipate or retain heat.

To stop sand getting in unwanted places while digging or when on the move the have some or all of these features (depending on species); a tough piece of skin that can be drawn over the nostrils, long hair at the base of the outer ear, and long eye lashes.

To enable themselves to run at great speeds bipedally they have evolved with three middle foot bones; the metatarsals fuse to form a single cannon bone. This provides extra strength and support, and also lifts it from its feet to its toes when running.

Large bulbous eyes make use of the little available light during their nocturnal activities.

During very hot periods of the summer Jaculus species will aestivate - a kind of reduced hibernation. By aestivating and lowering their metabolic rate they can live a long time on little energy. It allows them to 'stick out' the hardest of times.

One of the most surprising abilities is that of being able to go without a direct source of water - they do not drink - their metabolism produces enough moisture from the diet. The kidneys highly concentrate the urine (without being toxic to the animal) while the intestines extract all the moisture they can from the faeces.

The jerboas have three main types of locomotion; when pottering around it will move on all fours, when hunting or moving medium distances it will move each limb independently in a series of strides, when at full speed both limbs works simultaneously to get most thrust.

J. jaculus is thought to be the most highly specialised of all jerboas.

Housing

Although not hugely large, both species require a large area in which to run, they really will make use of all the space you can give them. A three-foot aquarium for a pair of J. jaculus and a four foot for a pair of J. orientalis are the bare minimum sizes, and really should be at least one foot or more longer.

The substrate should be of wood shavings or more ideally sand to the depth of around four inches. Bedding should include hay, straw, raw wool, tissue paper and other dried vegetation.

If wood shavings are used as the main substrate then a sand area or bath should be provided, otherwise the coat will become streaky and greasy.

A nest box can be given and will be appreciated. I suggest a design similar to that of below for J. jaculus with sizes scaled up 50-100% for J. orientalis.

It is suggested that additional lighting be used to stimulate natural cycles. This can be achieved with a standard florescent tube light places across the top of the tank, ideally with a daylight emulating tube used. Also suggested is a heating light (the sort available for reptiles) placed at one end the tank so when resting the jerboas have a range of temperatures to choose from.

The cage may be furnished with branches, stones, dried plants and small bushes. The latter two are often shredded to use as bedding.

The temperature should be kept between 15-30 degrees Celsius, with a natural dip at night. Good ventilation is necessary especially at higher temperatures and warm bedding at the lower end of the range.

In the wild they will experience a temperature range from 10 degrees Celsius at night to 50 degrees Celsius during the day in summer. Although it is at the hottest temperatures that they aestivate.

Feeding

Firstly we should address the decision whether to give standing water or not. This is an area of some controversy; some say that they should be given water in captivity while other say that they should not be given it, as is in the wild. I tend to go with the latter opinion for the following reason: Thousands of years of evolution has produced the animal with very efficient organs to deal with the extreme lack of water in the desert, then suddenly to have all the water they could require and more cannot be beneficial to the animal as the finely tuned organs will be 'overloaded'. Similar to the principle of giving Degus sugar after their metabolism has evolved without it. I think offering standing water to desert jerboas will cause kidney failure/damage leading to premature death.

In the wild they will eat roots, sprouts, seeds, grains, and sometimes, cultivated vegetables. It varies depending on availability and time of year. This diet should be simulated in captivity.

A suggested diet plan is below: -

Due to their not having standing water it is always good to give some 'wet' food source - for example the apple or sweet potato.

Behaviour

J. jaculus is thought to be a solitary animal in the wild but in captivity seem to prefer to be in pairs, though sometimes fighting occurs, which can be quite dangerous when the sharp claws on the powerful hind feet are involved.

J. orientalis is highly sociable and have been observed in the wild in groups of 2-3 and in larger groups in captivity.

You will find that they will sleep either on their sides or hunched forward to accommodate the long legs.

Although predominantly silent the jerboas are capable of producing grunts and shrieks when stressed or scared, and tapping of the hind leg is audible in some species - presumably to a similar effect of the rabbit - as warning signal.

You will observe both J. jaculus and J. orientalis 'playing', they will chase each other, your hand or even themselves. They will frolic about and stretch satisfyingly their hind legs from one extreme to another.

Breeding

There has been a lack of success with breeding jerboas in captivity, I feel this is majority due to lack of experience and knowledge rather than refusing to breed.

Some success has been achieved with each species though greater with J. jaculus.

I believe production and survival of litter is best attained by keeping the adults in pairs - this is certainly true for J. jaculus. The males may stay with the female during and after birth.

The female of both species has eight mammae.

Wild Status

During 1999 and 2000 surveys take of the Sharjah Emirate - likely jerboa areas. Unfortunately all bar one section was extinct of jerboas. This decline is most likely due to the reduction of their natural habitat coupled with the capturing of these animals. The degradation of habitat does not allow populations to recover. It was noted that vegetation had degraded; few edible species replaced by the more invasive species.

Also the lack of rain over the last the few years has made the grazing of donkeys and camels have much more of an impact.