Hens vary their vocal repertoire and structure when anticipating different types of reward

The vocalizations of nonhuman animals are considered potential indicators of motivational or internal state. In many species, different call types, and structural variation within call types, encode information about physical characteristics such as age or sex, or about variable traits such as motivation. Domestic chickens, Gallus gallus, have an elaborate vocal repertoire, enabling investigation into whether reward-related arousal is encoded within their call type and structure. Twelve hens were given a Pavlovian conditioning paradigm using sound cues to signal the availability of two food rewards (mealworms, normal food), one nonfood reward (a container of substrate suitable for dustbathing), and a sound-neutral event (sound cue, no reward). A muted-neutral treatment (no sound cue, no reward) provided a baseline for vocal behaviour. Sound cues preceded a 15 s anticipation period during which vocalizations were recorded. Hens produced a 'Food call' (previously defined in other studies) in anticipation of all rewards, including the nonfood reward. 'Food calls' and 'Fast clucks' were more prevalent in anticipation of rewards, and most prevalent following the cue signalling the dustbathing substrate, suggesting that this reward induced the most arousal in hens. The peak frequency of 'Food calls' made in anticipation of the dustbathing substrate was significantly lower than those made in anticipation of food rewards, potentially reflecting differences in arousal. Vocalizations that reliably indicate hens' motivational state could be used as measures of welfare in on-farm assessment situations. Our study is the first to reveal variation in the frequency-related parameters of the 'Food call' in different contexts, and to show the prevalence of different call types in reward and nonreward contexts, which may have implications for welfare assessments. (C) 2017 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.