Responses of Instrumentally Conditioned Starlings to Aversive Acoustic Stimuli

Abstract

Comparative data for responses of instrumentally conditioned starlings (Sturnus vulgaris) to pure tone and distress cry stimuli are presented. A direct relationship was obtained between score (a measure of the repellency) and intensity of pure tone at 1,000 cps. This relationship was also obtained when a recorded starling distress cry was used as a stimulus. Juvenile birds had lower scores (were less affected) than adults for both stimuli at all levels of intensity tested. Different frequencies of pure tone, from 1,000 to 7,500 cps had similar repellent effects on the birds. Increasing the duration of distress cries from 2 to 95 seconds, resulted in no significant changes in repellency scores. When the cry was played continuously the birds required less time to habituate; hence, presenting a stimulus for short periods may be more effective as a repellent. The average score of a distress-cry test was approximately 11 times greater than a pure tone trial at the same decibel level. This paper reports techniques for presenting acoustic stimuli and evaluating their repellent properties. Effects of intensity, frequency, and time of exposure of pure tone and recorded distress cry stimuli are discussed. The instrumentally conditioned behavior patterns of starlings were measured. Recorded acoustic stimuli have been widely used in attempts to repel nuisance birds. Basic procedures have been to play the stimuli at a high intensity either continuously or intermittently (Frings and Jumber 1954, Pearson et al. 1967). Under natural conditions, previous workers found that it was difficult to obtain comparative data in order to evaluate the effectiveness of the stimuli; therefore, other techniques have been used. Physiological phenomena, such as heart rate (Thiessen and Shaw 1957, Thompson et al. 1968) and behavioral responses, such as head shake and tail twitch in penned Peking ducks (Thiessen et al. 1957) have been used to evaluate the effectiveness of aversive acoustic stimuli. 1 Technical Paper No. 2537, Oregon Agricultural Experiment Station. We wish to acknowledge the statistical advice of W. S. Overton, Department of Statistics, Oregon State University. T. G. Scott, Department of Fisheries and Wildlife, Oregon State University provided encouragement and support in this research. V. Bogatich and K. H. Larson, U. S. Fish and Wildlife Service, assisted in obtaining birds. B. J. Verts, Department of Fisheries and Wildlife, Oregon State University and R. C. Simon, Oregon Cooperative Fishery Unit, critically reviewed the paper. METHOD AND MATERIALS Instrumental Conditioning Instrumental conditioning is a psychological technique whereby animals are trained to make a specific response for a reinforcement. In this study, birds obtained food when they made correct responses but incorrect responses were unrewarded; hence, the bird was instrumental in reinforcing its response (Underwood 1966, Ratner and Denny 1964). Feeding cycles (when rewards were available) occurred at predetermined intervals throughout the day. The time allowed for each feeding cycle was constant.