All rats (Rattus nmvegicuS), wild or tame, have a well-marked tendency to explore their surroundings. Wild rats, but not tame ones, also tend to avoid unfamiliar objects in a p r e~o w l y explored, and therefore familiar, area. The effect of environmental change on feeding waa studied in three groups of wild rats. Rats of Group 1 were accustomed to feeding from a wire basket at the back of the cage; for them the change consisted of transfer of the food to an unfamiliar tin at the fkont of the cage. Group 2 had food in the basket throughout, and the change consisted only in an empty, unfamiliar tin being put in the h n t of the cage. The rats of Group 3 fed from a basket in the front of the cage; the change for them was the placing of an unfamiliar empty tin between the back of the cage, where they slept, and the food. In all three group feeding was interrupted by the change. In the first group, three of the five rats stopped eating completely for one or more days; in the other two groups, food consumption waa merely reduced on the first day after the change. The ?heck in eating was not due to exploration: the new object waa at first completely avoided by all the rats. Tame albino and hooded rats,, subjected to the same procedure as the wild rats of Group 1, investigated the tin and the food in it at once; their food intake during the day after the change waa unaffected. The first approach of the hooded rats to the new object was, however, more hesitant than that of the albinos. Investigation of a new object, or new conditions, can sometimes lead to an interruption of feeding in tame rats, but this has nothing in common with avoidance behaviour in wild rats. PqcJwl. 48, 23846.cubed diet for mice and rats.

SUMMARY Wild rats (Battus norvegicus Berkenhout and R. rattus L.) were kept in large cages fitted with nest boxes and supplied with excess food and water. Colonies varied in size from four to twenty rats, and were usually maintained for at least nine weeks. The rats were individually identified and their behaviour studied in detail. Rattus norvegicus. In all‐male colonies there was a low mortality and most of the rats increased in weight. In colonies containing both males and females, mortality was high among the males, very low among the females; most of the males declined in weight, though some grew well. There was however no fighting for females. It is suggested that the extra fighting which took place in these colonies resembled displacement behaviour and was due to excitement evoked by the presence of females combined with frequent frustration. There were no deaths in all‐female colonies, or in colonies of litter mates. Unless parturient, normal females did not display aggressive behaviour except in ‘play’. Males, but not females, added to established colonies, were attacked by resident males and usually died, sometimes within a few hours and often without visible injury. At the beginning of an experiment there was much exploration, both of the cage and of the other rats. Social relationships were established early. Male members of the colonies fell into three classes: (i) alphas, which were the equals or superiors of other males in the colony, and attacked newcomers; (ii) betas, which adapted themselves to a subordinate role, and were ingratiating towards newcomers; (iii) omegas, which were persecuted by one or more alphas and soon died. Alphas and betas gained in weight; omegas lost weight. There were more omegas in male‐female colonies than in those consisting only of males. Amicable behaviour (apart from coitus and care of young) was shown by both sexes and was based mainly on contact ‘releasing’ stimuli: the most specific of a number of amicable responses was crawling under the belly of another rat. Fighting involved a series of stereotyped acts, including tooth chattering and a characteristic threat posture; there was much wild leaping, but biting produced only superficial damage. Rattus rattus. A small number of experiments with R. rattus showed that this species possesses all the components of amicable and aggressive behaviour observed in R. norvegicus, but that it is less fierce and more agile. There was no evidence of extra conflict in male‐female colonies. All‐male colonies containing both species were usually peaceful. R. rattus of either sex added to norvegicus colonies were usually attacked, but not with such intensity or consistency as were male norvegicus; if attacked, they died. R. norvegicus males added to rattus colonies were sometimes attacked, but they did not die. Displacement behaviour and abnormaľ sexual and aggressive behaviour were observed in both species. General. There is no reason to think that dominance hierarchies ever develop in wild rat colonies. Members of a single famil...

Summary Since 1953 laboratory mice have been bred continuously in an environment kept at – 3° C. Control stocks are kept at 21° C. All mice have cotton wool bedding. The effects of the cold environment are reviewed, and related to observations on other species exposed to cold. Physiological adaptation The principal physiological adaptation, of a small mammal exposed to cold, is increased heat production. Inbred mice, fully adapted to – 3° C., expend up to 4–5 kcal./100 g. body weight/hr., or about four times that of controls at 21°C. This is probably a maximum, maintained only outside the nest and for short periods. Colon temperature is unchanged; skin temperature, though high (31 °C. at the surface), is lower than at 21° C. (34° C.). Virgin female inbred mice at – 3° C. eat about twice as much food, per unit body weight, as controls at 21° C. The difference during late pregnancy is, however, much less; and, relative to body weight, consumption during the first 10 days of lactation is lower at – 3° C. than at 21° C. There are fewer young at ‐ 3° C. The lactating females may eat the maximum they can digest. Food is probably utilized more efficiently at ‐ 3° C. than at 21° C. Lowered external temperature reduces activity. Mice in a cold environment economize in general exploration of their environment; they also do no ‘functionless’ gnawing of friable materials. After increased heat production, the most important adaptive response is nest‐building. When accustomed to a cold environment, mice build better nests than in a warm one. But, given unfamiliar nest material, in a novel situation, they build a nest less quickly at – 3° C. than at 21° C.‐another example of economizing in energy. On exposure to cold, an increase in body weight would be adaptive. Some wild mammals increase their weight and body fat in winter. But adult laboratory mice, after transfer from 21 to ‐ 3° C., lose weight, largely owing to loss of fat. In this they resemble laboratory rats transferred to a cold environment. Similarly, inbred mice reared at ‐ 3° C. are usually lighter, at all ages, than controls at 21° C. Appendages, especially tails, are usually shorter in a cold thanin a warm environment; in mice the caudal vertebrae are shorter. The extent to which this reduces heat loss is not known. A genetically mixed stock of mice, selected for fertility at ‐ 3° C., developed longer tails during eighteen generations in the cold. Laboratory rats, after a few weeks at about +4° C., alone, without nests, have heavier liver and kidneys, intestine, heart and adrenal glands, than controls. Exposure in groups, or to seasonal cold, evokes different responses. In cold‐adapted inbred mice of the first or second generations reared at ‐3′ C., stomach, intestine, liver, and heart are heavier than those of controls. Insulation by hair is slightly increased at ‐ 3° C., though the heat‐conserving effect of this is small; the weight of the cropped skin is reduced in inbred mice, but it was unchanged in a genetically mixed stock after twelve generations in a cold...

Feeding behaviour has been studied in rats (Rattus norvegicus Berkenhout) kept in small cages in which a choice of foods was offered. Most of the rats were wild, but some albinos were used for comparison. The main intention of the experiments was to elucidate the component activities which make up feeding behaviour; but some observations on food preferences were made. When offered minced liver, wheat grains, flour and sugar, rats usually ate some of each food; sugar was eaten least, and sometimes little of e i t h e r flour or wheat was taken. When offered the alternative of wheat mixed either with cod liver oil or aniseed oil, as against wheat mixed with arachis oil, consumption was almost confined to the arachis oil mixture. This was true even when, as nestlings, the rats had been given only the distasteful mixture to eat. Both wild and albino rats show very marked exploratory and sampling behaviour during feeding. Evidence is presented that this is a pattern in its own right, and not merely appetitive. Its function is to make possible the rapid learning of topography, and especially the whereabouts of food, water and shelter. Sampling is also important in enabling rats to associate particular physiological actions, whether nutrient or toxic, with different foods. Exploration and sampling occur even when the situation and the foods are familiar, and regardless of age or sex. Continued sampling makes possible regular reinforcement of learned preferences. It also enables rats to change rapidly from a familiar but distasteful food to an unfamiliar but palatable one. Sampling is not stopped by 'satiation', but is released by it. In wild rats, but not albinos, there is highly developed flight and avoidance behaviour. This tends to reduce the dangers of exploratory behaviour. Both wild and tame rats tend to feed in cover when this is practicable. This has indirect social effects, since one rat may rob another in the nest. Social influences on feeding are only incidental. Often they are a product of associative learning. There is no parental guidance of young, nor imitation by young of adults. Displacement grooming was seen when hungry rats were deterred from feeding by the unfamiliarity of the situation; and in other frustrating circumstances. It is concluded that much of the feeding behaviour of wild rats can be interpreted as a resultant of the opposed effects of exploration and sampling on the one hand, and flight and avoidance on the other.

A critical analysis is presented of some features of exploratory behaviour, especially in wild and tame rats but also in other species. Such behaviour is considered in the light of certain general concepts, especially ‘appetitive behaviour’, ‘reactive inhibition’, latent or exploratory learning, and motivation. The avoidance of new things, displayed by wild rats, is also discussed.