5. Social Housing

5,1. Pair Formation and Pair-Housing of Monkeys

How do you go about pairing previously single-caged monkeys to address the animals' need for companionship?

5,1,1. Adult Cynos (Cynomolgus/Long-Tailed Macaques)

I have had great success with pairing cynos. For some reason, adult males have been much easier to pair than females (Figure 44). Cynos don't always group well, but they make pretty good pairs!


Figure 44 These compatible adult male cynos are engaged in grooming each other. Photo by Richard Lynch.

I usually start with a clear, transparent panel between the two intended partners. From this I can usually gage how the socialization will go:

Most of the time, I know within the first 30 minutes whether things will work out when I eventually give the two individuals full access to each other.

Using a similar familiarization technique, Lynch (1998) and Watson (2002) tested 48 adult male cyno pairs and found that partners were compatible in 94 percent of cases.

5,1,2. Adult Rhesus (Rhesus Macaques/Monkeys)

Is the pair formation technique that we have discussed for adult long-tailed macaques safe for adult, especially male, rhesus macaques?

With slight modifications, I have used this technique successfully with adult male rhesus. I always screened four animals at the same time in a cage arrangement that allowed the animals visual and auditory contact through transparent doors. Dyads who exhibited consistent, unidirectional dominance/subordinance behavior were first allowed simultaneous access to a central activity cage, while still maintaining access to their home cages, for 30-minute sessions daily for one week. Criteria for potential pair compatibility were:

Partners of such pairs were subsequently re-evaluated when they had simultaneous access to the activity cage for progressively extended, up to 48-hour, sessions in the course of six weeks. Of 15 dyads tested in this manner, 80 percent (12/15) turned out to be compatible during six-week test periods (Figure 45; Roberts and Platt, 2005). We formed also three adult male cyno pairs in this manner. All three pairs were compatible.

Figure 45  Ray and Max, two rhesus males, have lived together as compatible companions for eight years. The two are assigned to a timed breeding program of a caged rhesus colony. Photo by Viktor Reinhardt.

If you consider the circumstances under which the animals are forced to live together, day-in-day-out with no private space, their degree of partner compatibility of about 80 percent is truly amazing. How would our relationship with a loved person develop if we had to live under conditions similar to those of pair-housed macaques in research labs?! Human primates who chose to marry each other and live in an environment that allows for some private space, become incompatible in over 50 percent of cases. I guess, we could learn something from monkeys, who are caged permanently in the same boring environment, just by observing them!

I have formed same-sex pairs of carefully pre-familiarized adult female and adult male rhesus and checked their compatibility over a period of one year: At the time of pairing and throughout the follow-up year, female pairs were compatible in 88 percent of 77 cases, male pairs were compatible in 80 percent of 20 cases (Reinhardt, 1994b).

The PI who does research with our pair-housed rhesus insists that cage companions be separated during the night and on weekends, so that they cannot fight and injure each other while nobody is around. I would love to keep the animals together also during the night, but cannot argue with the PI because I really don't know if that would jeopardize the safety of the animals.

In our facility, compatible companions are allowed to remain together also during the night, on weekends and holidays. This applies for both female and male pairs, as well as for all animals who have head cap implants. It has never happened that we found paired animals injured or bruised when entering their room in the early morning. I think there is no special risk when pairs spend the night together without being supervised.

We also keep our male and female rhesus pairs together 24/7 and encounter no problems related to aggression during the night. Articles by Crockett et al. (1994) and Lynch (1998) make it clear for paired male cynos that partners engage in more fighting, when they are re-united every morning, than when they are allowed to remain together also during the night. It is probably more risky to have companions go through a brief re-introduction procedure each morning than stay together also during the night.

At our facility, after pairs have been established, they are housed together uninterruptedly. This includes male and female isosexual pairs, and each species housed here, including rhesus, pigtails, sooty mangabeys, squirrel monkeys, chimps, and cynos. We have not noticed that paired companions fight during the night, on weekends and holidays when nobody is around.

Based on my own experience with a large number of pair-housed rhesus macaques, I would not recommend separation during nights/weekends/holidays as a preventative measure. Generally, when things are quiet with the people, things seem quiet with the monkeys! And any time you separate, you run the risks of someone forgetting to re-unite, or re-uniting the wrong animals; and on top of that, it's a lot of work for the staff.

5,1,3. Adult Baboons

How do you establish pairs of male baboons? I currently work with 38 animals, ranging in age between 2 to 6 years. I have paired male rhesus and pigtails successfully but have no experience with baboons.

I have introduced male olive baboons of that same age group you mention. At this age, they are relatively easy to work with. First, I observe two potential partners in a familiarization cage in which they can communicate with each other through a clear Plexiglas cage divider. Good signs of possible compatibility are:

I always allow several days "howdy" time to make sure that the two animals are well familiarized and establish a dominance relationship, which often is not noticeable until they share the same living quarters. Partners, who got along well with each other as neighbors, are subsequently introduced in another unfamiliar cage where they have no reason to engage in territorial conflicts. I establish new pairs always on Mondays, so I have the whole week to check them daily and assure that they remain compatible.

5,1,4. Adult Vervets (Vervet Monkeys)

Does anyone of you have experience with the same-sex pair-housing of adult vervet monkeys?

It is my experience that it makes no difference to the outcome of pair formation, whether the partners were first familiarized or not. Adult female pairs are compatible in about 60 percent of cases. We have never managed to house adult males in pairs, unless they were reared together right after weaning (8 to 10 months), in which case compatibility is about 90 percent.

5,1,5. Young Monkeys

Is it necessary to also pre-familiarize potential companions when working with young animals who have not reached the age of puberty?

With juvenile cynos, I usually don't take the trouble of pre-familiarizing them, but simply put them together. I have never had a pair that was incompatible.

I also skip the familiarization procedure with rhesus who are three years old or younger. These young animals spontaneously get along with each other, probably because dominance-subordination relationships are not yet firmly established. When they are over three years, they typically show dominance status ambitions—especially young males—which makes it very advisable to allow them to establish their rank relationships during a familiarization period before introducing them as a pair. I am always inclined to reduce the risk for the animals to an absolute minimum, even if it means that I have to invest a bit of extra time.

5,1,6. Paired Monkeys Competing over Food

When monkeys are housed in pairs, is competition over food and perhaps even monopolization of food by the dominant partner a problem? If so, how do you deal with it?

I notice this problem in about 10 percent of our pair-housed rhesus monkeys. I tried cooperative feeding for a while. It works if I come in early enough to feed the monkeys myself. Due to time constraints, however, I typically separate the "problem" monkeys with a solid panel until both animals have eaten their portion. Of course, separating monkeys daily for 15 to 60 minutes isn't ideal.

You don't really need to train or separate the partners. When I started pairing rhesus and stump-tailed macaques in double cages, I noticed very quickly that some animals had difficulties getting access to one of the feeders, because the dominant partner tried to monopolize the food. In some pairs, the subordinate animal got so intimidated that he or she no longer made serious attempts to get food while the dominant partner was eating. The installation of dividing panels with a passage hole close to the back wall of the cage (privacy panels) solved this issue (Figure 46), by allowing both partners to obtain food, each from a separate feeder, without seeing each other. I don't remember a single case in which food competition was a problem after this new cage design was implemented throughout the colony of more than 700 pair-housed macaques.


Figure 46 A privacy panel with a passage hole at the back wall of the cage allows paired macaque companions to get away from each other's field of vision. This minimizes agonistic interactions and avoids competition over access to the food boxes (Reinhardt and Reinhardt, 1991). Photo by Viktor Reinhardt.

5,1,7. Conclusions

In order to minimize the risk of injurious antagonism upon initial introduction of two strange adult monkeys, it is advisable to allow potential companions to first get to know each other and establish a dominance-subordinance relationship without option of direct physical contact. This pre-familiarization is not necessary for juvenile animals. Potential food competition between paired cage mates can be circumvented by designing the cage in such a way that the two animals can each access a separate feed station without seeing each other.

5,2. Sex Difference in Partner Compatibility

Is there a sex difference in terms of compatibility/aggression when you keep animals in same-sex pairs?

It is my experience with rhesus and stump-tailed macaques that male-male pairs are equally compatible — and equally affectionate —as female-female pairs:

We keep same-sex pairs of marmosets, and have more problems with fighting between the females than the males. Usually female pairs are okay when they are still young, but when they reach the age of 3 to 4 years, they often start fighting. When this happens, we have to separate the incompatible partners in many cases. It is then very difficult to re-pair them with another female, and we consequently end up with quite a number of single-housed individuals. We have to deal with this age-related social incompatibility also in males, but the incidence is less frequent.

Your observations question the validity of the often-published notion that "males are more aggressive than females." It's true, males may inflict wounds that are more serious when they bite than females, but this doesn't mean that they are more motivated to show aggressive behavior in the social context.

5,3. Making Use of the Stress Buffering Influence of a Companion

There is scientific evidence that the presence of a compatible conspecific can buffer stress reactions not only in people (Bovard, 1959) but also in rats (Davitz and Mason, 1955; Conger et al., 1957; Latané, 1969; Taylor, 1981; Sharp et al., 2002), mice (Goldsmith et al., 1978), guinea pigs (Kaiser et al., 2003; Machatschke et al., 2004), sheep (Fraser, 1995), goats (Pearson and Mellor, 1976; Lyons et al., 1988), and monkeys (Mason, 1960; Coe et al., 1982; Coelho et al., 1991). Do you make use of this stress buffering effect with the animals in your charge?

5,3,1. Post-Operative Care

We have mice who are recovering from telemetry-implantation while being housed either alone or in pairs. With several years of experience with this surgery, we now are pretty sure that socially housed mice "feel better" than individually housed mice. Our mice are anesthetized with O2N2O and isoflurane. They regain consciousness within a few minutes after surgery, are kept in an incubator for one hour, and then returned to their group mates in a heating mat-provisioned home cage. We have encountered no problems, and it never happened that group members would bully the recovering animal or remove sutures.

I can add here an observation of a colleague who performs spinal cord surgery in rats. He lost about 20 percent of the animals when these were individually caged after surgery. Defying tradition, he tried keeping the rats in compatible pairs after surgery. This caused no complications. He then implemented pair-housing for all his post-operative rats. This had the effect that he no longer lost any of his animals. Unfortunately, he has not published this experience and, obviously, does not want to go back to individual-housing to get proper scientific data to support this observation.

It is my experience with rhesus macaques that it is advisable to pair-house an animal after surgery as soon as possible with his or her compatible companion. We do this especially with pairs, after one of them had cranial implant surgery. It is the investigator's and my own impression that the animals recover better from the surgery stress when their familiar companion is with them than when they are alone (Figure 47). The presence of a companion provides a psychological support that the animals seem to need during post-operative recovery. I should perhaps emphasize the obvious, that we establish new pairs well before surgery and always make sure that the animal who had undergone surgery has regained full consciousness before the companion is brought to the post-surgery recovery cage.


Figure 47 Young female rhesus macaque recovering from cranial implant surgery in the company of her adult cage mate who is tethered during an experiment. Photo by Viktor Reinhardt.

Murray et al. (2002) demonstrated the practicability of post-operative pair-housing in 15 female cynos who were returned to their partners on the day of the operation (placement of vascular access port). Change in hierarchy status, self-traumatic events, weight loss or diarrhea did not occur in any of these animals, and the incision sites healed unremarkably. The animals ate and drank normally, and they accepted their postoperative oral medication without problem.

Close to 95 percent of our cyno population is pair-housed. The animals are subjected to a lot of orthopedic procedures. There have never been problems with the re-pairing of the animals after surgery. We partition the pair's cage with a transparent panel, which we remove after the treated companion has fully recovered from anesthetic effects (usually 24 hours). It has never happened that animals who had no surgery showed any negative behavioral reactions toward their temporarily probably weaker cage mates.

In a small study, we compared post-op recovery of the animals when:

We found that there was:

when the animals were re-paired with their partners, than when they were kept alone after surgery.

5,3,2. Chair-Restraint

When I worked at a primate research facility, my primary motivation for implementing pair-housing was prompted by individual rhesus monkeys, who were assigned to research protocols requiring chair-restraint. These animals were tested alone in sound-proof chambers. Their behavior made it very clear that they experienced anxiety and fear, not so much because they were restrained, but because they were alone—apart from the sporadic presence of the investigator or animal care personnel, who unknowingly frightened rather than comforted the monkey. It took me a whole year to coax the PI into pair-housing all 40+ monkeys assigned to this particular research project. What a difference it made! Whenever an animal was chair-restrained, the compatible companion was now brought along in a mobile cage, allowing both partners to keep uninterrupted visual and acoustical contact with each other (Figure 48). This calmed the restrained monkey, who no longer exhibited behavioral signs of distress, such as open-mouth threat, teeth grinding, restlessness, and refusal of food treats.


Figure 48 The distress associated with being chair-restrained all alone in a strange room can be buffered by the presence of the familiar cage companion in a mobile cage. Photo by Viktor Reinhardt.

If circumstances do not allow conspecific companionship, the attending care personnel with whom the restrained animal has a trust-based relationship can possibly act as a stress-buffering substitute. When my monkeys are chaired during an experiment, I stay most of the time with them, talking to them reassuringly. I have the feeling that my presence has a strong calming effect on them, and this actually is the reason why I do it with consistency with all my monkeys.

5,3,3. Chronic Diarrhea

It is not unusual for a rhesus monkey to develop chronic diarrhea after being removed from his or her social group and transferred to a single-housing condition. I have often noticed that, once an animal has been returned to his or her group, the diarrhea stops. Some cases of diarrhea can clear within a week or two when an animal, who has been kept for a long time in a single-cage, is transferred to a compatible pair-housing arrangement.

We had good success by creating a "chronic group" of ten previously single-caged rhesus who had all been labeled as "chronic diarrhea." They were given pepto tabs in the group for the first couple of weeks, but we slowly decreased as needed. Eight animals were cured by this socio-medical treatment, with no relapse occurring during a follow-up period of over two years.

The fact that transfer to social-housing can sometimes cure previously single-caged macaques from chronic diarrhea, suggests that companionship boosts an animal's immune system thereby increasing an animal's resistance to certain pathogens. There are published reports supporting this hypothesis:

5,3,4. Conclusions

Empirical evidence suggests that social animals recover better from surgery when they are not alone, but when a compatible companion is with them. Empirical evidence also indicates that companionship helps rhesus macaques cope with confinement stress, as manifested in chronic diarrhea.

5,4. Capture of Group-Housed Animals

It has been documented repeatedly that group-housed primates can easily be trained to cooperate during the capture procedure (Rose et al., 1975; Smith, 1981; Taff and Dolhinow, 1989; Reinhardt, 1990; Sainsbury et al., 1990; Luttrell et al., 1994; Kessel-Davenport and Gutierrez, 1994; Klaiber-Schuh and Welker, 1997; Lynch et al., 1998; Mendoza, 1999; White et al., 2000). What about rabbits and rodents? What tricks do you use to catch individuals living in a group, without causing undue disturbance/distress?

5,4,1. Rodents and Rabbits

If you offer rats a food treat, about half the time you pick one of them up for any kind of procedure that is not invasive, they will all come running to you, eager to be picked up and rewarded. This part is simple, but the challenge is to select the right one from the crowd.

I am using the same trick, also with great success. When catching rats in this manner, they show hardly any resistance during subsequent daily injections, a circumstance that drastically decreases injectional wound lesions.

Food reward is the keyword also for mice. They love chicken pellets and will come to the front of the cage to get some, even when this implies that they are picked up, briefly restrained and injected.

Guinea pigs are very skittish when their pen is opened. However, they will predictably run into shelters from which they can easy be retrieved (Gray, 1988).

As for rabbits, they also will come to the front of the cage and allow you to get hold of them, if they can trust you and if they can expect a carrot, a piece of bread or any other food reward.

5,4,2. Cats

Our institution has socially and individually housed cats, all living in large pens. As part of the cleaning procedure, the cats have to move into holding areas and return after their pen has been cleaned. Usually they do not cooperate and have to be caught one by one. Many of them do not like to be handled, so it has been an ongoing challenge to shift them in and out of pens. We've even had a few injuries resulting from handling our more grouchy cats.

This has never been an issue for me. As soon as I look through the window of their room, our cats all perk up and run to the door to meet me. To then catch one of them is nothing very special, and I don't think it upsets any of the cats, including the one that I will have to take out for a procedure. I assume that my success here is based on the fact that I quite often visit the animals, play with them, and do nothing that could make them afraid of me; they trust me.

I recently brought in a laser pointer to play with our cats and soon discovered that I can prompt individual cats, and even pens full of kittens, to move wherever I want them to move, without catching them but simply by using the laser as a target. I bought our staff laser pointers, and we've found that it's an effective way to move cats for routine procedures. Not only that, but trying to catch the quickly moving "laser prey" is also entertaining for the cats. They get to exercise and play a fun game every day. I've only seen one male cat who is not interested in chasing the laser.

We hang the laser pointer outside the cat room next to the little window in the door, so that passing-by technicians can play with the cats by shining the laser into the room, and enticing the animals to chase the moving light dot. The technicians and the cats enjoy this game, which provides entertainment to both parties. Amazingly, no one walked off with the laser pointer.

5,4,3. Conclusions

While group-housed monkeys are easily trained to cooperate during the capture procedure, rats, mice and rabbits can be induced to come forward and be picked up by luring them with a food reward. Guinea pigs tend to be more timid but will run into a shelter in which they can then be caught. Cats can be picked up without much ado if they have nothing to fear from you. If they shun you, they will follow a laser point to the location you want them to move.

5,5. Social-Housing of Cats

Cats tend to be rather solitary animals, but seem to prefer companionship—with the option for privacy!—over being caged alone. Is permanent social-housing a species-adequate option for cats in research labs?

We house groups of female cats on a permanent basis; the animals do just fine. Newcomers get integrated without serious fighting. Our cats have access to airline crates, boxes, other hiding places and plenty of elevated resting surfaces (Figure 49). We give them several litter boxes that we exchange daily. In order to circumvent conflicts associated with food, and assure that each cat gets enough, we partition the daily food ratio of a group into more portions than there are cats and distribute them on different locations of the room.

Figure 49 Sufficient resting surfaces so that each cat in a room can have her own "private" space avoids competition and possible aggressive interaction. Photo by Geoff Loveridge; reproduced with permission of the Institute of Animal Technology; published in Animal Technology 45(2), 69-87, 1994.

For many years we have kept same-sex groups of up to 18-month-old cats without encountering serious aggression-related issues. Initially, we had more problems with the girls than the boys, but we were always successful in bringing order back into a group of females, by putting a castrated male into their group. We try to keep the groups as stable as possible and, especially,avoid removing cats whom we consider to be the main players in the group. Good care staff, who are encouraged to get to know all the cats in their charge very well and are given extra time to establish good relationships with them, is a major factor to assure that cats living in groups remain compatible over time.

As long as they are not participating in research studies, our cats are kept in groups in a spacious room. They are all spayed or neutered, a circumstance that makes it unproblematic to keep all of them in a social setting. Bernstein and Strack (1996) kept 14 cats of both sexes (but all neutered) in a room that was furnished and managed in cat-appropriate ways, and found that the animals did co-exist "amicably."

Permanent social-housing of cats can be a safe arrangement under the condition that the primary enclosure is properly structured and the personnel committed to providing high-quality care. If all animals of a group are spayed or neutered, the social-housing of cats is relatively unproblematic.

5,6. Social-Housing of Dogs

How are facilities housing their dogs? Specifically, how are you housing pairs and trios and larger groups? Have you found an ideal number of dogs to house together? Are you using bedding material and platforms?

We keep most of our dogs in pairs or trios, but feed them individually to avoid food competition. They all have daily access to a spacious outdoor pen in compatible groups of five to ten dogs. All males are vasectomized. This allows us to house our dogs together regardless of gender, but we do take the precaution of temporarily separating our bitches when they are in heat. In each dog room, we have six or 12 individual pens that can be interconnected as needed. The floors of the pens are solid. We do not use any bedding. Each pen is provisioned with one platform.

The optimal number of dogs per housing unit depends on the breed, and most importantly, the dogs' temperament. Hickey (1993) describes a well-tested, species-adequate caging arrangement and cage furniture for dogs housed in groups of three who are assigned to toxicological studies in which individual food consumption can be monitored.

It seems to be practical and relatively safe to house dogs in small groups of three in convertible runs that allow for the separation of the animals during feeding times and are provisioned with an elevated platform.

5,7. Exercise for Dogs

How do you get a dog to "exercise" in the research lab setting?

It is a legal requirement in the United States that dogs kept in research facilities are given the opportunity to "exercise" (United States Department of Agriculture, 2002). There is, however, no consensus how this can/should be accomplished. To release a dog alone in a large but barren "exercise area" would not be a sensible way of complying with the law. There is no reason to believe that a dog would actually run around alone and play with himself in such an empty, albeit large enclosure (Figure 50).

Figure 50 A large but unstructured exercise area is unlikely to prompt a dog to actually exercise, i.e., run around and play. Photo by Hillis Miller; re-designed by Annie Reinhardt.

My current facility uses dogs from Class A vendors. For the most part these dogs don't do much running—unless you run with them—don't pay much attention to other dogs, and rarely play with toys. They mostly enjoy either sitting next to people or being petted. Interestingly, the dogs we have adopted out settled into more typical "dog" behaviors in their new homes: sitting on furniture, running in the yard and barking at other dogs. They never, or very rarely, displayed these activities while in the research facility. We've not been able to identify the source(s) of their apparent "discomfort" that causes them not to express more "expected" canine behaviors. They just aren't rambunctious, and getting them to "exercise" isn't an easy task, when they seem much more interested in just sitting in your lap while you talk to them. Putting them on the floor while cage changing/cleaning, or leaving them in a room to play by themselves does not really help.

Campbell et al. (1988) studied beagles in barren enclosures and noticed, not surprisingly, that regardless of the size of the cage, the dogs did not exercise unless people were present in the room. Hughes et al. (1989) concluded from a similar study that human contact is the single most consistent and important factor in encouraging dogs to be active.

Our dogs get daily human attention in a play room. We teach them tricks for treats, groom them, play with them, or just sit with them quietly. Each member of the staff is responsible for one or several dogs, and this includes walking each dog once a day for at least 30 minutes (Figure 51). I can't overemphasize how important human contact is for these animals.

Figure 51 Walking a dog on a leash provides exercise, improves staff morale and helps with re-homing the dogs after research completion. Photo by Novo Nordisk A/S, Denmark.

Playing with dogs and walking them on a leash on a daily basis is probably the most effective and appropriate option to provide dogs with the opportunity for exercise in accordance with animal welfare regulations.

5,8. Social-Housing of Pigeons

Can anybody on the forum share first-hand experiences regarding the refinement of the traditional housing practices of pigeons?

Our pigeons have been singly caged for as long as 15 years. Not surprisingly, many of them have developed stereotypies such as feather picking, over-preening, head bobbing and circling.

Recently we built a large flight pen and group-housed up to six pigeons at a time. We took the oldest 15 to18-year-old male pigeons first and introduced them in the spacious flight cage. Well, they simply froze; they were terrified! We waited for 30 minutes and then added four females, who had a bit more sang-froid about them and were eager to investigate and hang out with the other birds. It then did not take a long time for all pigeons to settle down and adjust to sharing the big enclosure with each other. They seem to be compatible, and since they live together in the flight pen, I have not noted a single incidence of stereotypical behavior.

Finding the right match may be a challenge, but pigeons—just like any other social animals—do benefit from being housed with other compatible pigeons in a relatively large flight pen, versus being housed alone in small, barren cages.

5,9. The Lone Pig—Addressing His or Her Social Needs

Is anyone in charge of pigs who are kept alone with no other animal in the room? How do you deal with the fact that your pigs are social/herd animals who have a strong need for companionship?

People have successfully used mirrors with sheep (Parrott et al., 1988; McLean and Swanson, 2004) and cattle (Piller et al., 1999), but pigs just don't respond the same way to mirrors. We require regular human interaction for our individually housed pigs, just as we do for our dogs (Figure 52). Someone would go in and sit, pet, brush, even walk the pig.

Figure 52 Regular interaction with friendly personnel helps pigs to cope with the distress resulting from being caged alone. Photo by Scottish Agricultural College.

Weekends and holidays can be very lonely for the pigs in a room by themselves. In the past, we had purchased two mini Yucatan barrows solely for companionship to research-assigned pigs, who would otherwise have been alone. We paid for their per diem out of our Enrichment budget. These two pigs were allowed to move about a large area freely. They became everybody's spoiled pets—it was great for morale! They had a good influence on new pigs assigned to research. The new-comers were always high strung and nervous in the beginning, but after a couple days, seeing us interact with their neighboring buddies, settled in quickly and were soon willing to be handled by us. We have since retired the two Yucatan pigs and, unfortunately, didn't manage to get replacements yet.

Regular interaction with friendly personnel or permanent visual and auditory contact with another pig living in the same room are good compromise solutions to address the need for companionship of pigs, who have to be single-caged for research reasons.

5,10. Mixing Different Species

Is it a good or a bad idea to keep different species in the same room, or perhaps even in the same enclosure?

It was always my understanding that mice are fearful of rats—who are natural predators for mice—and that stress can be induced in mice by exposing them to the scent of a rat (Calvo-Torrent et al., 1999; D'Arbe et al., 2002). We recently performed a small study in which we assessed urinary corticosterone—as stress indicator—of mice, when rats were present in their room. We did see a stress effect in the mice during the first week. After that, it appears that the mice got used to the presence of rats.

I have housed small rabbits and guinea pigs together, starting out as a pair when they were still very young. They remained together for seven years, often sleeping alongside each other. I have seen problems when large rabbits were housed with guinea pigs. This does not mean that the rabbits are aggressive, but the little guinea pigs are at a certain risk of being knocked over and "flattened" when the big rabbits bounce around in their general enthusiasm.

While it may be okay to house different species together it would not be a good idea to keep animals of a prey species together with animals of a predator species—e.g., mice and rats—in the same room.

5,11. Why are Male Mice Housed in Trios?

Why are male mice so often kept in groups of three rather than in pairs?

I've heard that one reason for housing mice in trios is that if one mouse becomes aggressive, he will "share" his aggression amongst the other two males. If the mice were housed as pairs, all this aggression would be released on only one male.

This sounds a bit weird, but who knows? Even if this would reflect reality, would it benefit the quality of research data collected from these animals and, hence, justify the trio-housing? I am wondering if the level of aggression-related stress and the incidence of injurious fighting, is higher or lower in pair- versus trio-housed male mice. If a particular housing system is given priority, there should be hard data demonstrating benefits not only in terms of money—which I assume is the case here—but especially in terms of quality of scientific data and animal welfare.

No scientific data have yet been published that would support the prevailing trio-housing of mice.

6. Stories

6,1. The Bucket Monkey

Many of the messages posted here can be quite serious as we try to find answers to our questions and solutions to frustrating problems. Well, I thought that I would share a funny story to help everyone laugh and take a breather.

We have four rhesus girls, each housed in a large activity cage. Piglet—named appropriately!—loves water. She will follow me around as I am cleaning her cage just so she can play with the water jet. She swims too. Yesterday I decided to fill a pumpkin bucket with water for her. Well, for whatever reason she came up with, the bucket ended up on her head! She proceeded to walk around the cage bumping into things and changing direction. She would walk on two legs, then crawl on four. She would do this intentionally. Every once in a while she would take the bucket off, look around and then do it again. She's such a little ham!

6,2. The Rope Mice

I have just had all my beliefs in the sleeping behavior of mice and their preferences for shelters soundly smashed apart when I visited a local pet-shop: Domestic mice were kept in a large cage containing an igloo shelter, nesting material, cardboard tubes, a cardboard box, a wood shavings substrate and a 2 cm-thick hanging rope that was attached to the ceiling of the cage with a hook. Who would like to guess where the two mice were sleeping?

In the open corner huddled together?

On the hook?

Well, the mice were sleeping on the very top of the rope! One appeared to have slung herself over the hook through the knot at the top of the rope, and the other was clinging, but apparently asleep, to the knot at an angle that was almost vertical! These were standard mice being sold as pets—not arboreal miniature lemur or anything like that! There were plenty of "suitable" sites under cover—which I always thought was the major feature that mice desired for sleeping. I was surprised to see the mice so near to the lights in the roof, thinking that they would prefer dark areas for sleeping. I would have also thought that, because warmer air rises, sleeping in the top of the cage would not really help them cool.

That's typical for animals: they always prove us, i.e., the human mind, wrong.

Your story just demonstrates so nicely that animals are not little machines but mysterious, unpredictable, fascinating creatures. I vividly remember waking up in our tent several years ago and seeing two little mice curled up right above us in the cup-shaped mosquito net of the tent's roof. They slept in the bright morning light, visible to the birds—and to us—without any protection whatsoever. Why? Because all the burrows were occupied that particular morning?

6,3. The Escapees

I once had a rat escape and get inside an old radiator on the wall. Funny how dumb I was about it. I spent ages trying to reach in, stick things through the ventilation holes to get the critter and cut holes at various points. An hour later it was getting dark, the rat and I were both grimy and annoyed, and we were glaring at each other through the grill of the heater. Finally I stopped and thought: "What do rats like? Places that are familiar, dark and enclosed." I put the rat's home cage near the hole where she had entered the radiator, and turned off the light. Thirty seconds later she was captured and returned back home.

I had a very similar experience with a hamster who not only escaped but disappeared. During the night, the fellow simply gnawed a hole into the wall and dug his way under the floor of the room. You could hear him shoving material out of his way to build a burrow. However, he got hungry, and I counted on that. The next morning, he came up, sniffed the air and headed straight for the carrot, where I could catch him and put him back into his cage, then give him the well-earned carrot.

We are working on a project in which we film mice during the dark phase with infrared light. The technician working on the project is now analyzing the videos from several weeks ago. She told me yesterday that the cameras had caught three mice escaping from a cage—the lid hadn't been replaced properly—then getting back in several hours later! As far as we were concerned, the mice had never gotten out of the cage. We would not have known about this if it hadn't been for the camera. I wonder how many other mice go for midnight walks unnoticed!

I had a chicken called Roadrunner who was a terrible escape artist. She could open her cage by finding her way around various pegs and twist ties. Once free, she would lurk around under the cages and slip out when someone opened the door. She would then lurk around in the rafters until someone opened the outside door. I swear she had very definite escape plans; none of this wandering around in plain sight! She got out of the building on several occasions. Fortunately, the building was in a rural area and she only got a short distance before being startled by a sheep and freezing, so I could grab her and bring her back home.

6,4. The Monkey in the Box

We hang boxes—the kind used for organizing small storage items—with a double clip from the tops of the cages of our pair-housed squirrel monkeys. They are a big hit and many of the monkeys spent hours swinging back and forth in the boxes. One pair had a history of one partner "beating up" on the other, stealing treats and pushing him off the perch.

One morning, we heard a terrible screeching, and upon investigation, found the normally subordinate squirrel monkey swinging back and forth in the box with a firm grip on the head fur of the normally dominant monkey. As the box swung back and forth, the poor guy getting his fur pulled was also being pulled back and forth in the cage. We corrected the situation quickly and added a second box, which was instantaneously grabbed by the now dominant monkey, leaving the other box for his partner. This restored peace.

6,5. A Near Accident in the Swimming Pool

We had a near accident in the little swimming pool for our cynos, when an adult female was swimming underwater and a big male started playing around, like a cat chasing after a mouse, from outside the pool and, finally, jumped on the female's back. He put his hands around her neck and appeared to be deliberately holding her under in the 1 meter deep water. After about 15 seconds, I panicked, since I thought he was actually drowning her. I rushed to the scene to "interfere," but just at that point he released her and retreated. She shot out of the water like a rocket and was really angry with him, screeching and with rage in her eyes. He looked surprised, and like he had made a significant error, ran screaming away from her as she chased him down and bit him a good one and repeatedly slapped and pinched him. The whole time, he was acting submissively toward her, lip smacking wildly, and ducking as she continued to clobber him.

The two have been in the pool together many times since then, but the female never takes her eye off the male even when she's under water (as cynos dive with their eyes open).

6,6. The Friday Bath

We give our pair-housed rhesus girls a "bathtub" on Fridays. The tub is a rat cage filled with water placed in the tunnel of the two interconnected cages (Figure 53). At first, they didn't know what to do. I then put a carrot in the basin to help them get closer to the water. Soon enough, they were dipping their hands in the water and fished for the carrot. Kuaui would sit there and stare at the carrot with her hand above the water. Then, suddenly, she'd lunge her hand in and grab it. This girl was full of spunk! In the end, I had them all sitting in the water.

 Figure 53 Long-tailed macaques love water; they are good swimmers. Photo by Natasha Down.

Tejas goes under water and keeps her eyes open, while Kuaui dives with her eyes and mouth open! Since the rat cage is transparent, I can see everything. The two are quite hilarious! I am surprised they can fit themselves into the bathtub, but they love it!

7. Working With Animals

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