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Tonic immobility tests were used to obtain information about the levels of fear in end-of-lay hens after they had been transported to four commercial processing plants. They stayed in a condition of tonic immobility longer than hens which had only been caught and removed from cages. There was no evidence that they became habituated to transport during journeys of up to five hours, but there were significant differences between the levels of fear expressed by birds transported by the different processors.
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Mills et al. (1990) studied this question.
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