The effect of stress on the vocalizations of captive poultry populations

Date of Completion

January 2010


Agriculture, Animal Culture and Nutrition




The economic and wellness impact of stress on production and health of chickens cannot be over-emphasized. There have been several attempts to measure stress response in animals. Conventional methods of measuring stress are not necessarily good indicators of welfare as they detect stress only after it has negatively impacted the chickens. In the light of the problems associated with stress detection, there is a need to non-invasively measure stress early enough to enable the farmer to remove the stressor before it adversely affects the chickens. This dissertation evaluated the use of chicken vocalizations as an indicator of stress in chickens. ^ The vocalizations of chickens of varied ages, breeds and sex were recorded and analyzed using the modified Hidden Markov Model (HMM). The living conditions of the birds were altered and resultant vocalizations were analyzed in context. Control environments were also created and vocal recordings were made to compare with the stressful vocalizations. Analysis of chicken vocalizations using the HMM revealed that the model achieved an average classification accuracy of 74%. The HMM was also able to detect and distinguish between stressful and non-stressful vocalizations with 100% accuracy within 120 ms, making the model a good tool for early stress detection. ^ The acoustic characteristics of newly hatched chicks' vocalizations under natural and stressful conditions. Significant (P<0.0001) differences in the vocalization pattern of both groups were detected by Praat sound analysis software. To investigate the robustness of the HMM for stress detection, the effect of stress, age and diet on broiler chickens' vocalizations was determined. It was observed that vocalizations made by the older birds had a classification accuracy of greater than 90%. Using the intensity of chickens' vocalizations, habituation to human presence was determined in white leghorn birds. The intensity of the vocalizations of control hens was no longer significantly different from stressed birds after 3 week of exposure to human presence. Additionally, the hearing ability of chicken was determined using a comparative study of chickens' Auditory Brainstem Response (ABR) due to the effect of age, sex and production type. It was seen that in chickens, the peaks occurred later in younger birds than older ones. Sex and production type did not have any effect on the latency-intensity curve of the birds. In conclusion, this dissertation demonstrates the use of chicken vocalizations as a reliable indicator of stress in chickens and its potential use in early stress detection. ^