Behavioral correlates of olfactory and trigeminal gaseous stimulation in chickens, Gallus domesticus.

Despite growing evidence of avian olfactory abilities, there are few reports of behavioral correlates of chemosensory stimulation in birds. The present study aimed to determine how the behavioral responses of hens to selected gases might be affected by input from different chemosensory systems. We also hoped to relate electrophysiological thresholds previously measured in our laboratory to behavioral evidence of perception. Immediate behavioral responses to ascending series of short (7 s) pulses of olfactory (hydrogen sulphide), trigeminal (carbon dioxide) and combining (ammonia) gaseous stimulants were measured in 12 partially restrained adult hens (Gallus domesticus) using a purpose built gas delivery system. The concentration ranges applied matched those used in our previous electrophysiological studies of olfactory bulb responses. Consistent and specific behavioral responses were observed in response to stimulation with each gas. While significant increases in mandibulation (a distinctive rapid bout of bill movements), interruption of ongoing behavior, orientation to the end of the stimulus, and struggling were seen during stimulation with all three gases, orientation towards the stimulus occurred only in response to the olfactory stimulants, ammonia and hydrogen sulphide. The only gas to elicit significant avoidance was hydrogen sulphide, while gasping and headshaking were elevated in response to stimulation with carbon dioxide. Approximate threshold values for some types of behavior related reasonably well to receptor thresholds determined electrophysiologically, but perception may have occurred at lower concentrations without overt behavioral consequences. The diversity of the behavioral responses observed supports the notion that the gases selectively stimulated different sensory pathways.