NEPHEW, B.C.*; AARON, R.S.; ROMERO, L.M.; Tufts University: Effects of Arginine Vasotocin on the Corticosterone, Heart Rate, and Behavioral Responses of Starlings to Crowding

Arginine vasotocin (AVT) has been previously shown to have significant effects on heart rate (HR), plasma corticosterone (CORT) concentrations, and numerous behaviors in independent studies. In this study, we examined all three of these variables simultaneously to obtain a more complete picture of AVT�s role following crowding, an ecologically relevant stressor. The study consisted of eight HR transmitter implanted resident Starlings being subjected to combinations of 3 conspecific crowding treatments (0,1,5 intruders) and 3 AVT treatments (saline, 1ug, 4ug AVT), for a total of 9 treatments. The subcutaneous AVT doses were given prior to 30 minutes of pre-intrusion, which was followed by 30 minutes post-intrusion. Treatments were videotaped for behavioral analysis, HR data was collected, and basal and post-intrusion blood samples were obtained. The resident CORT data indicate that there was no effect of intruders on CORT, although the 4mg AVT dose did significantly elevate CORT. In contrast, in the intruders, both AVT and intruders significantly increased CORT. However, while CORT levels increased with increasing AVT in the 1 intruder treatments, they decreased with increasing AVT in the 5 intruder treatments. Behavioral analysis of the residents revealed significant decreases in feeding, drinking, preening, and beak wiping following injection of AVT when pre and post-intrusion data were combined. Increasing conspecific density resulted in elevated aggression, but this increase was attenuated by AVT. Although analysis of the HR data is not complete, the present results suggest that the CORT response of Starlings to crowding and AVT�s role in this response is dependent on social environment, and that AVT may suppress crowding-induced aggression in resident Starlings.