Avian Mobbing Behavior and Predator Recognition

Abstract

In a series of experiments, stuffed specimens of owls were used to represent predators. The species used were the Screech Owl (Otus asio), the Horned Owl (Bubo virginianus), the Burrowing Owl (Speotyto cunicularia), the Short-eared Owl (Asio flammeus), and the Pigmy Owl (Glaucidium gnoma). Some of the Screech Owls, Burrowing Owls, and Horned Owls were fairly realistic in appearance. The rest of the owls were typical museum study skins, with their faces turned upward and with cotton eyes. All these specimens differed from live owls in that they were motionless and silent. The owls were placed either on objects upon which a live owl might perch or on a set of collapsible poles that could be arranged to stand 8, 16, or 24 feet high. The specimens were placed in a wide variety of habitats, including those in which the species that was being used might naturally occur and those where it was presumably absent. Most of the experiments were carried out in various parts of Los Angeles County, California. The remainder were conducted in Tehama, Butte, and Nevada counties of California, and in Washoe County, Nevada. Certain requisites for the sites of these experiments were established. The sites were in areas which (1) had a population of small birds, (2) were near cover suitable for the birds, (3) were reasonably free from interruptions by people, (4) had not previously been used for such experiments, and (5) were as far as possible from known or suspected nests. The second qualification was adhered to so that the responses of the birds would not be limited. The fourth qualification reduced the possibility of previous conditioning to the site of the experiment, such as was demonstrated by Nice (1943). The fifth requirement was an attempt to avoid the familiar hypersensitivity of birds that are near their nests.