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GREAT BLUE HERON A From this position, an aggressor can thrust the bill at an opponent, although such attacks are not frequent. The Full Forward behavior, however, can result in serious injury and even the death of an opponent (Forbes and McMackin 1984). "Bill duels," in which opponents alternately attempt to C The Birds of North America, No. 25, 1992 B Figure 2. Breeding displays of the Great Blue Heron. (A) Forward display; (B) Stretch; (C) Bill duel. By D. Otte, from Mock (1976). A. Poole, P. Stettenheim, and F. Gill, Editors grab each other's head (Fig. 2c), occur during some Full Forward displays. "Circle Flights" involve a heron taking flight with the neck extended and parallel to or below the axis of the body; used by territorial herons along boundaries and by nonterritorial herons pursuing one another. In the "Arched Neck" display the neck is fully extended above or parallel to the body axis with a down -curve in the distal portion; used by territorial herons after preening, stretching, or long periods of inactivity, during short flights within a territory, while walking and wading, and while flying to a roost or colony site. Also used by herons in pursuit flight, when flying from an approaching heron or predator, or when supplanted by another individual. Displays on the foraging grounds may be analogous to displays at the nest (R. Bayer pers. comm.). Communicative interactions between chicks and their parents need study. SPACING Individual distance. Nonterritorial herons from neighboring colonies overlap foraging grounds (R. Bayer pers. comm.). Individual distance on foraging grounds and at nests maintained by displays and aggressive interactions (Bayer 1984b, Mock 1976). Territoriality. Adults defend territories along rivers, creeks, mudflats, and lografts day and night (Bayer 1978, Butler 1991). Territories maintained by displays, threats, and chases (Bayer 1984b). Territorial herons rest in exposed sites from where they display and launch chases of approaching herons (RWB). Mean length of shoreline of 32 territories in Yaquina estuary, OR 355 m (SD = 168); mean area: 8.4 ha (SD = 5.4); in freshwater marshes (n = 7 territories): 129 m (SD = 28); mean area: 0.6 ha (SD = 0.1; Bayer 1978).