Development of locomotion toward home nesting material in neonatal rats

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Abstract
Neonatal rats were individually placed in a narrow choice zone between home and fresh nesting materials. At Day 2 postpartum the pups made significantly more home‐choosing responses (vs responses for fresh nesting material). At a mean of 5.6 days (range, 4 to 9 days) the pups reached a criterion of 2 consecutive days of responses all for home nesting material. The number of head contacts increased abruptly upon reaching the criterion. In a 2nd experiment we observed that the pups which were repeatedly tested performed no better than those which were tested for the 1st or the 2nd time. Thus, (a) home‐seeking responses appear to emerge substantially earlier than previously reported by other investigators, (b) head‐contact responses appear to be related to successful home‐choosing, and (c) some maturational rather than experiential factors are important for the development of both head‐contact and home‐choosing responses.