Open-field behavior in domestic chicks tested individually or in pairs: Differential effects of painted lines delineating subdivisions of the floor

The open field is a common test of fear, but the apparatus varies widely. Lines painted on the floor facilitate measurement of locomotion (areas entered), but, though some animals balk at lines, this variable has received little attention. In Experiment 1, 10-day-old female chicks were tested individually in an open field with an unmarked floor or one delineated into areas by 1- or 3-mm-wide black lines. In Experiment 2, chicks were tested in pairs in the presence or absence of 3-mm-wide lines. Strong intraindividual correlations demonstrated that both paces and areas entered are effective measures of locomotion. Chicks tested individually were unaffected by the presence or width of lines. Conversely, pair-tested chicks paced and pecked more when the floor was delineated. Given the latter findings, some standardization is recommended.