vocalization

Although the two primary functions of vocalization are to defend territory and to attract mates, vocalization also has the function of indicating behavior and comfort levels. Chickens begin to vocalize soon after hatching and continue to do so until they decease. In a 2013 study by researchers at Università degli Studi di Milano in Italy and the University of Bristol in the United Kingdom observed the vocalization patterns of broiler chickens during the first 38 days of the chickens' lives. The study consisted of using specialized microphones to record and compare the sounds of baby chicks when they were all together in their hen house and when they were socially isolated. A sample of the recordings is depicted below in Figure 8. The researchers found that, "As soon as the first chick was moved into the enclosed box, the vocalizations immediately increased in repetition rate, both inside and outside the box, showing that social isolation in chicks led to an increase in rate of vocalisation" (Fontana et al, 2013).

A more recent study published in 2020 and titled "Assessment of Laying Hen's Thermal Comfort Using Sound Technology" observed the vocalization patterns of hens in response to changes in their environment's temperature. The vocalization patterns are described below in Figure 9. The environment's temperature-humidity index (THI) was organized as follows: a comfort zone of THI < 70, an alert zone of THI 70 - 75, a ddanger zone of THI 76 - 81, and an emergency zone of THI > 81 (Du et al, 2020). The study explains that the occurances of different calls correlated with the temperature of the chickens' environment.