Anybody who keeps animals has the potential, by dint of careful observation, to discover something hitherto unrecorded about them and thus to extend the boundaries of scientific knowledge. I keep mostly rodents and several times I have noted things about them which I have not found in any reference book.

Some while ago I wrote an article for NAPAK Animal News in which I expostulated my strong suspicions, based on practical experience, that Steppe Lemmings (Lagurus lagurus) are, in fact, sugar intolerant and should not be given fruit in their diet. Below I outline new conclusions I have drawn about Wild Cavies and Harvest Mice. I must emphasise that these are my own experiences which may differ from other keepers’ observations. I hope that if anybody has conflicting views, they will contact me to tell me my hypotheses are unsubstantiated rubbish!

Harvest Mice (Micromys minutus)

Recently I had two separate colonies of Harvest Mice. Colony A was kept in a 36" glass tank with plenty of climbing facilities, “finch-type” nesting baskets, and a deep layer of hay. Intended as the main breeding group, I deliberately kept the numbe of individuals in this tank fairly low. Colny B was kept in a 12" plastic (“Pen-Pal”) tank. Because this second tank was uite considerably smaller than the first,I was compelled to have far fewer furnishings in it: just a small wooden sleepingbox and a few twigs for climbing. This housed the “over-flow” colony and thus it contained slightly more individuals than in the original group.

The two tanks were kept in separate locations. Colony A was in my main rodent breeding room, where it was in close proximity to numerous other rodent species ranging from Nile Rats (Arvicanthis niloticus) to Spiny Mice (Acomys sp.). Colony B, on the other hand, was in a subsidiary breeding room containing fewer other species.

I was surprised when specimens from colony A (the larger, less populated tank, remember) indulged in tail and ear nipping (although I never actually witnessed any bullying), with the sad result that few specimens were completely “intact”. Perversely, the mice in colony B (those in the smaller tank) were all in excellent condition with perfect ears and complete tails. If anything, one could perhaps have expected the reverse situation. What, then, was going on?

I can only conclude that the mice in colony A were able to smell the other rodents nearby, an odour imperceptible to me, with my typically feeble olfactory sense, but all too detectable to the Harvest Mice. Some of these other species, such as the rats, could be considered potential predators of Harvest Mice. I believe, with the benefit of hindsight, that the close proximity of these larger species contributed to stress within the Harvest Mouse colony, manifesting itself in high levels of redirected aggression within the colony. The mice in colony B, on the other hand, were surrounded by far fewer other rodents and consequently did not indulge in this self-destructive behaviour. Comments, please?

Wild or Brazilian Cavies

Eight species belonging to the genus Cavia are generally recognised, including the domestic Guinea Pig (Cavia porcellus). I have kept and bred the Brazilian Cavy (Cavia aperea) successfully for a number of years and have supplied several other breeders and institutions, including Marwell Zoological Park, with surplus animals. The species is popularly thought to be the ancestor of the domestic Guinea Pig, largely on the basis of anatomical similarities, in particular the crest of hair on its neck.

This theory has been reinforced by crossbreeding and biochemical studies. Results are not conclusive, however, and it remains equally likely that other species of cavy are implicated instead. There are two other possible contenders; these are Cavia fulgida (the Shiny Cavy) and C. tschudii (the Montane Cavy).

It is possible that the Guinea Pig is derived from any of these species, or perhaps even from a hybrid of all three. The jury is still out.

The behaviour of the Brazilian Cavy is very different from that of its domestic relative, being a very nervous animal that does not enjoy being handled. They are quite good at climbing (unlike domestic Guinea Pigs) and have even been known to make vertical leaps or to scramble up wire netting if suddenly startled.

Although the Brazilian Cavy breeds readily in captivity, I and several other breeders have experienced very high infant mortality, the young dying usually within minutes or hours of birth. In most cases the babies are just found dead first thing in the morning, often in a mutilated condition and even, on occasion, partially eaten.

The reason for the high death rate within the crucial first 24 hours is unclear but, having thought long and hard about this, I now believe that the breeding male is responsible for killing the babies, either deliberately or, more likely, inadvertently. The fact that the young are often found in a partially eaten state is probably incidental, many rodent species opportunistically consuming the bodies of other members of the colony that have died from natural causes, although one is at first surprised to find such cannibalistic behaviour in the normally vegetarian cavies.

The female comes into season again almost immediately upon giving birth, although receptivity lasts for less than half a day. Males congregate around the female when the birth is imminent, with the alpha male aggressively guarding her from younger, subordinate males. It is he who generally mates her first following parturition. If, for whatever reason, he does not mate with her, the other males seize their opportunity and will pursue and mate with her. I now believe that, in the confines of the pen, the males’ persistent solicitations are preventing her from attending to the needs of her new-born offspring.

Even when just one male is kept, his repeated attempts to mount the female can be hazardous to the new-born young. It is probable that the babies, in attempting to suckle, are simply getting in his way and are crushed to death.

The solution, obviously, is to remove the male before the young are born. However, it is not always possible to tell when the female is pregnant as these animals are naturally quite rotund anyway, so now I allow the male to run with the females for up to sixty days (the gestation period averages 62 days, with a range of 60-70 days) and then remove him to another pen to allow the females to give birth in peace.

Cavies are very sociable animals and a male, housed by himself, is a miserable and lonely animal, often going off his food and sulking. It is therefore a good idea, if possible, to place with him a young male or a spayed female for company.

I have never had any trouble reintegrating him into the main group once the babies are weaned, unlike some other rodents which are notoriously difficult to reintroduce to each other after a period of separation.