Tonic immobility (TI) test is used to assess the fearfulness of birds. However, its outcomes depend on many factors including the breed, species, and restraining position. This study aimed primarily to evaluate the effect of different restraining treatments on TI parameters in both chickens and ducks. Secondarily, it aimed to identify the associations between various variables measured in this study including body weight, handling time, induction attempts, and TI response. Two separate experiments were conducted in broiler chickens and mule ducks. TI was performed on ground level in chickens and on a U-shaped cradle in ducks. Briefly, 30 broiler chickens (34 d of age) and 18 mule ducks (55 d of age) were randomly assigned to three restraining treatments: left lateral position (LLP), right lateral position (RLP), and back or dorsal position (DP). The variables measured in both experiments were body weight (BW …