The purpose of these experiments was to investigate nipple attachment in laboratory rat pups during the first 24 hr of life and to identify determinants that influence its expression. In Experiment 1, nipple attachment was shown to be age dependent: 1-hr-old pups exhibited a low percentage of attachment, and 12-and 24-hr-old pups exhibited high percentages when tested against an anesthetized lactator. Experiments 2-6 .investigated several factors that might influence the nipple-attachment time course. These experiments clearly established the time course as age related. Experiments 7-10 explored the behavioral mechanism responsible for the increase in attachment from Hour 1 to Hour 12. They showed that nipple experience, independent of milk acquisition, was the responsible factor for the increase. The findings suggest that learning is employed as a behavioral strategy by the newborn, and they reemphasize the value of using species-relevant measures in the assessment of behavioral development.

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