NEPHEW, B.C.; KAHN, S.A.; ROMERO, L.M.: Heart rate and behavior change independently of corticosterone following acute auditory and visual stressors

Captive European starlings (Sturnus vulgaris) were subjected to five acute stressors: a visual stressor (strobe light), an auditory stressor (loud music), and disturbance by three different humans; their accustomed caretaker, an antagonist (the experimenter), and a novel human. Behavioral, heart rate (HR), and corticosterone (CORT) responses to each stressor were recorded simultaneously in starlings subcutaneously implanted with HR transmitters. Behaviorally, both the auditory stressor and the human antagonist caused a significant increase in preening behavior without subsequent increases in activity, beak wiping ( a behavioral indicator of displaced aggression), or bouts of feeding and/or drinking. The visual stressor elicited a significantly depressed maximal HR response of ~550 beats per minute (bpm) compared to the ~700 bpm recorded following the other four stressors. In addition, the time it took for the HR to return to basal levels (335 bpm) was significantly shorter following the strobe. In contrast to the stressor-specific differences in HR and behavior, all five acute stressors elicited similar sub-maximal CORT responses. Although it has been shown that pigeons are capable of distinguishing between individual human faces, and anecdotal evidence implies that wild populations may be capable of identifying individual researchers, we found no significant difference in either HR or CORT responses to three diverse human intrusion stressors in starlings. Taken together, our data indicate that starlings modulate behavioral, HR, and CORT responses differently depending on the stressor, and that these three pathways are regulated independently.