Recorded Calls of the Eastern Crow as Attractants and Repellents

Abstract

The eastern crow (Corvus brachyrhynchos) often becomes a nuisance because of its feeding and roosting habits. As with other pest birds, many ideas for control have been tried, but none has proved fully satisfactory. As a continuation of our attempts to use recorded sounds of biological significance to influence behavior of pest birds (Frings, et al., 1954, 1955), we have recorded the calls of the eastern crow and have studied the reactions of crows to broadcasts of these recordings. The calls were recorded on tape (at 73, in./sec.), with either a Pentron Model 9T-3C or an Ampex Model 350P tape recorder. Recordings were made in the field by concealing microphones near roosting or nesting places of wild crows and monitoring from concealment nearby. The reactions of the birds to their natural sounds were thus observable. From these recordings, copies were made on continuous-loop tape cartridges played by a special player (Bird-E-Vict) through a Stromberg-Carlson Model AU 42 amplifier and University Model PA 30 speakers. The objectives of the study were mostly practical, and therefore no attempt was made to record the complete repertoire of calls nor to test fully all that were obtained. Bent (1946, pp. 247-249) reviews earlier studies on calls of crows, but we find it impossible to compare the calls we recorded surely with the syllabic renditions given by earlier workers. Recordings were made of nestlings, juveniles, and adults. Attempts to capture wild adults for possible distress calls proved fruitless. Two calls were found early in the work to have pronounced effects, and these were tested most carefully. The first, an assembly call, is given by crows that have sighted an owl or a cat. The crows gather nearby and join in a strident chorus of sharp caws. This call, when recorded and broadcast, is remarkably attractive to crows. We have tested it under many different conditions in Maine and Pennsylvania, usually without having crows within sight or hearing at the start, and in only 3 out of 30 tests have crows not come to the source of the sound within 1-5 minutes. If the speakers and observers are in the open, the crows approach near enough to see them and settle on some vantage point to observe. If the speakers and observers are hidden, the crows may come almost to them. At intensities up to 120 db. at 1 meter from the speaker-loud enough to be disturbing to man-crows have come practically to the source.