Burrows dug by albino rats were compared with those of wild Norway rats in an outdoor pen and in observation chambers in the laboratory. Burrows, in terms of measurements, configurations, or sequential development, were indistinguishable in wild and domestic rats. Burrowing for both wild and domestic rats was unaffected by raising in outdoor burrows, by availability of nesting material, or by pregnancy. Prior experience in burrowing did make it more efficient in a second trial, which suggests that learning may have a limited role in what appears to be a behavior with a strong genetic basis. Feralization of domestic rats in the outdoor pen was especially productive in answering claims of degeneracy in these animals: Albino rats were hardy throughout climatic extremes, they maintained a stable population for two years, they constructed and lived in burrows, and they showed a variety of wild-type behaviors. I don't think any behaviorists have considered studying a wild rat in the field just to see what it does. They might get very valuable information if they did. Konrad Lorenz, 1975, p. 63.Lorenz's speculation can be extended to domesticated rats: Behaviorists might also benefit from watching albino rats outside the laboratory. If domestic rats were kept outside, would they survive the rigors of feral living? Would they, after hundreds of generations in laboratory cages, dig burrows like those of wild rats? Initial help on this project was diligently supplied by Anita Settle, and assistance with construction was provided by Merlin Schnell. The outdoor pen was provided by X. J. Musacchia and C. C. Middleton and by the Sinclair Research Farm. Elizabeth Gilk provided generous assistance in some of the later tests. Gratitude also goes to a fellow researcher, E. 0. Price, then at the State University of New York at Syracuse, who refrained from further research on this topic when he discovered we had unknowingly started similar projects at about the same time. Portions of the present research were

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Five experiments with wild and domestic rats (Rattus norvegicus) were designed to assess behavioral effects of domestication. The results, which must be considered preliminary, are supportive of the notion that domestication in the Norway rat has induced an adaptive fitness rather than degeneration: 1. Scar-marked captives showed the poor reproductive success typical of traditional attempts at initial laboratorization. In 10 such pairs, three of the females killed prospective mates and five of the six who produced litters cannibalized all or some of the offspring. Unscarred captives, assumed to represent higher social status in the wild population, produced litters in eight of ten pairings with no abnormal breeding or maternal behaviors. 2. Scar-marked captives were least dominant in water competition and were most likely to show abnormal behaviors, new wounds, and mortalities. Similar competitive groupings of domestic rats showed the expected difference in social behavior; fighting was less intense, social distance was less, and threat signals were rare compared to wild rats. Where wild and domestic rats were housed together, however, the intensity of social behaviors in the latter increased, even leading to deaths, although interaction was almost segregated between the two kinds of rats. 3. In an avoidance learning situation, wild-caught and wild F1 (laboratory raised) rats were markedly inferior in performance compared to domestic rats in paradigms with internally or externally cued warnings. 4. In another avoidance learning context, wild rats showed limited evidence of a passive style of learning while domestic rats showed clear evidence of active avoidance learning. These data suggest that learning styles may differ in the two kinds of rats and that definitive evidence of a learning difference will be difficult to obtain. 5. Daily patterns of responding for drinking water were more resistant to change in the wild rats, even at a substantial cost in water obtained, suggesting that domestication may have induced greater behavioral flexibility.

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