The TI fear respons has previously been found to be amplified both by stressful events and by increased levels of the stresshormone corticosterone in blood plasma. As small broiler breeders in the current study display lower level of fearfulness through lower inducability, shorter TI-duration as well as shorter latency to first headmovement during TI, this may indicate a lower stress level in these individuals.

Vocalizations is a very important social tool for chickens and they display a wide repertoire of vocalizations. If socially isolated, chicks normally responds with increasing frequency of vocalizations, presumably in order to reinstate contact with conspecifics.
   The findings that small chicks vocalize both more and sooner than do large chicks in both the OF test and the TI test may hence be a sign of differences in social motivation or social reinstatement tendencies. Differences in sociality may have consequences in terms of coping with the normal housing environment of broiler breeders as this is a situation where social stimuli is presented in excess.