Two Unusual Foraging Behaviors of Great Blue Herons in Lincoln County, Oregon

Abstract

Great blue herons (Ardea herodias) rarely kleptoparasitize other birds (Willard 1977; Kushlan 1978; Brockman and Barnard 1979; Bayer 1985) or prey upon birds (Packard 1943; Palmer 1962; Olson and Johnson 1971; Bayer 1979; Chapman and Forbes 1984; Hancock and Kushlan 1984; Evens and Page 1986). In this note, kleptoparasitism of a double-crested cormorant (Phalacrocorax auritus) and the eating and stalking of red phalaropes (P1alaropus fulicaria) by great blue herons are described. At about 1525 hr PST on 9 December 1990 at Eckman Lake, a freshwater impoundment adjacent to Alsea Bay in Lincoln County on the Oregon central coast, I saw an immature double-crested cormorant dive and then surface holding an orangish, cylindrical fish about 10 cm long. For about 10 sec, the cormorant swam and turned its head from side to side while holding the fish crosswise in its upward-pointed bill. A great blue heron flew to the cormorant from a nearby Douglas-fir (Pseudotsuga menziesii) forested area. Splashing water obscured the ensuing 5 sec struggle. The cormorant then dived and surfaced about 15 m away, while the heron stood in 0.5 m deep water with the large fish in its bill. Kleptoparasitism is a function of prey size and handling time (Kushlan 1978; Brockman and Barnard 1979; Quinney et al 1981; Bayer 1985.) The conspicuous handling of a large prey item by this immature cormorant may have resulted from its lack of experience. At 1700 hr PST on 13 January 1991, I saw a great blue heron attempting to swallow a dead red phalarope along the Newport bayfront at Yaquina Bay, Lincoln County. The phalarope was swallowed head first after four unsuccessful attempts within 2-3 min of my initial observation. Between attempts, the heron used its bill to hold the phalarope crosswise around the middle of the body, shaking it at times. After the body-was swallowed, the wrist of one wing protruded from the heron's mouth for about 60 sec before swallowing was complete. A lump in the heron's neck was visible afterwards for approximately 5 min. Over the next 3 min, the same great blue heron stalked 15 to 20 phalaropes foraging within 10 to 20 m of its original position. First, the heron walked slowly with extended neck towards a small group of phalaropes, which swam about 5 m away. Maintaining an upright posture, the heron then walked quickly towards the phalaropes, which again flew about 5 m and landed on the water. Both of these stalking methods were tried unsuccessfully about five times on different groups of three to five phalaropes, but the heron caught no phalaropes during this observation time. For the next approximately 3 min, the heron attempted to approach the phalaropes from a board floating near the phalaropes. After climbing onto the board, the heron stood motionless, facing a phalarope group. Although the phalaropes swam within about 2 m, the heron did not strike. On two occasions when phalaropes approached, the heron raised and held its wings over the water for about 5 sec. Both times, the phalaropes swam away. After flying back from the board to the original mudflat location, the heron continued stalking phalaropes for approximately 3 min. It turned towards phalaropes standing on the mud or swimming in water a few cm deep, and with hunched neck, flexed legs, and forward-pointed bill, it ran quickly towards them into the shallow water. The phalaropes dispersed 2 to 3 m by flying or swimming. The heron returned to the mud and then to the floating board, watching but not stalking phalaropes from both points for 1 to 2 min. Approximately 12 min after my initial observation, the heron was flushed from the area by human activity. Red phalaropes occur sporadically during migration or after winter storms in coastal Lincoln County. Although no other dead phalaropes were seen in a visual search of the area, the heron may have scavenged a dead bird, as described by Kubisz (1989). Red phalaropes are not among the birds documented as great blue heron prey items (Palmer 1962; Brockman and Barnard 1979; Hancock and Kushlan 1984), although predation on a Wilson's phalarope was described by Packard (1943).