The Hunting Behavior of Eastern Screech-owls (Otus asio)

—We studied the nocturnal hunting behavior of eight radiotagged Eastern Screech-owls (Otus asio; five females and three males) during the period from November 1994 through March 1995. Screech-owls selected low perches when hunting (x = 1.66 m), presumably to obtain a clear view of the ground and an unobstructed flight path to prey. Low perches may also improve the ability of screech-owls to hear and locate prey. Screech-owls used perches at different heights when hunting different types of prey and also tended to perch higher when moonlight was available, perhaps because increased light levels permit owls to rely more on vision. Only 8 of 35 attacks were successful, and this low success rate suggests that owls were more often attempting to capture small mammals rather than invertebrates. Male and female screech-owls exhibited similar hunting behavior, with no differences observed in the types of prey hunted or in giving up times. Weather conditions and season (early winter vs. late winter) had little effect on the hunting behavior of screech-owls. While the hunting behavior of diurnal predators has been studied by several investigators (e.g., Fitzpatrick 1981, Greig-Smith 1983, Rice 1983, Sonerud 1992), few studies of the hunting behavior of nocturnal predators have been conducted (Bye et al. 1992). The hunting behavior of owls, in particular, is little known, with most information anecdotal or speculative (Bent 1938, Voous 1989). Consequently, little is known about how factors such as weather, moon phase (i.e., light levels), snow cover, sex, and temporal distribution of prey might influence the hunting habits of owls. Eastern Screech-owls (Otus asio) are small, nocturnal predators found throughout eastern North America (Johnsgard 1988). Researchers have examined several aspects of their behavior and ecology, including food habits (Craighead and Craighead 1956, Ritchison and Cavanagh 1992), home range sizes and habitat use (Belthoff et al. 1993, Sparks et al. 1994), nest site selection (Belthoff and Ritchison 1990), and the postfledging behavior of adults and young (Belthoff 1987). Very little is known, however, about their hunting behavior. __________________________________ Gehlbach (1994) gathered information concerning the hunting behavior of Eastern Screechowls in central Texas, however, observations were made only in suburban yards and in the immediate vicinity of nests. Thus, little is known about how screech-owls hunt in more natural habitats and at locations some distance from nest sites. Eastern Screech-owls apparently hunt in a sitand-wait fashion, using short flights to capture prey (Marshall 1967, Gehlbach 1994). It has also been suggested that Eastern Screech-owls may rely primarily on sight when searching for prey because they have symmetrical ear openings (Marshall 1967, Norberg 1987). Bye et al. (1992) suggested that Boreal Owls (Aegolius funereus) used low perches while hunting because they rely primarily on their sense of hearing. Thus, at least in Boreal Owls, sensory capabilities may play an important role in determining how prey are located and captured. This may also be the case for Eastern Screech-owls. The objective of this study was to describe the hunting behavior of Eastern Screech-owls during the non-breeding period. We specifically sought to examine: (1) possible differences between the hunting behavior of males and females, (2) seasonal and temporal variation in 1 Biologist with the City of Austin, TX. 2 Professor of Biology, Eastern Kentucky University, Richmond, KY.