Priorities for Future Research

The nocturnal Great Horned Owl is rarely seen or heard during standard breeding bird surveys, even where pairs are known to be present on nearby nests (CSH). A possible exception is the first few stops on Texas routes where dawn comes rapidly. In future, NOS results should accompany nest density data as the 2 most reliable indicators of long-term population trends.

Because boreal populations are cyclic and not entirely typical for other regions, it would be constructive to compare the lifetime reproductive success of cyclic populations with that of stable populations in the temperate zone and in arid regions where years of food scarcity are rare or irregular. Careful studies of the boundaries of the various subspecies, using breeding season specimens, are long overdue. More information is required on how many floaters are present in populations, on the age at first breeding (males and females), and on whether birds emigrating during food scarcity survive or even return to their breeding area.

Little is known about how territories are established, whether territory size changes with food availability, about the role of the sexes in pair formation and selection of nest sites, about hooting activity throughout the year, about responsiveness to the playback of hooting during censuses in different habitats, about the extent of individual and geographic variation in hooting, about the behavioral mechanisms and severity of territorial defense, and about sex-specific differences in the behavior of territorial birds and floaters.

The effects of different forestry practices on this species need to be determined. Month-by-month pellet analyses are still lacking for most regions. No one has used night telescopes to gather data on the number of minutes a female is absent from the nest, or on feeding rates at the nest. More research is needed on sex ratios, molt sequence, the extent and exact timing of molts in specimens of known age, the time of day of egg-laying, and the disposal of eggshells and feces in the nest. DNA studies could determine whether extra-pair paternity occurs.

The effects of the Great Horned Owl on other owl or raptor species, such as the northern Spotted Owl, and on species at risk (terns, plovers) need study.