Nicol, C. J. 1992. Effects of environmental enrichment and gentle handling on behaviour and fear responses of transported broilers. Applied Animal Behaviour Science 33, 367-380.

Enriched/handled birds were more active in their home pens than control animals. ..The most fearful birds were those which had been enriched [fabric squares, plastic rings, grass, perches, etc.] and handled, whilst the least fearful bird were enriched but not handled. Thus, environmental enrichment itself may have reduced the birds' reaction to novel stimuli. Obviously, the handling was not gentle, because the birds continued to attempt to avoid the experimenter even after 40 days of regular handling.