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GREAT BLUE HERON
<br />forage occasionally in dry fields. Along east coast
<br />of U.S., favors coastal marine habitats, especially
<br />salt marshes.
<br />FOOD HABITS
<br />FEEDING
<br />Main foods taken. Mostly fish but also
<br />amphibians, invertebrates, reptiles, mammals, and
<br />birds (Palmer 1962, Kushlan 1978, Verbeek and
<br />Butler 1989).
<br />Microhabitat for foraging. Different foraging
<br />habitats best explained by individual ability. In
<br />British Columbia, juveniles forage in grasslands,
<br />adult females in estuarine marshes and intertidal
<br />beaches, adult males along riverbanks (Butler
<br />1991). Microhabitats of yearlings poorly kn onn;
<br />include estuaries and beaches, p l
<br />visits to colony -sites (RWB).
<br />Food capture and consumption. Forage singly
<br />and with conspecifics; behavior flexible, diet
<br />varied. Hunt most often by slowly wading or
<br />standing in wait of prey in shallow water ( Kushlan
<br />1976, 1978, Willard 1977, Hom 1983); also hunt
<br />from floating objects (Godin 1977) and even -while
<br />floating;:SJensen 1932). Wade more slowly and
<br />stop for longer periods than other herons (Willard
<br />1977). Often forage in flocks with other Great Blue
<br />Herons (Krebs 1974), other ciconiiformes (Willard
<br />1977, Kushlan 1978), and Double- crested Cormor-
<br />ants (Phalacrocorax auritus; RWB). Forage -night
<br />and day on beaches (Black and Collopy 1983) and
<br />wharves (RWB); up to' one :third-- of total
<br />photoreceptors in ciconiiform eyes :.are: rods,
<br />presumably an adaptation fornight vision (Lish
<br />1982). Prey located by sight (Krebs and Partridge
<br />1973) and caught by rapid forward thrust of neck
<br />and head; then held between Mandibles. Most
<br />prey swallowed whole. Small mammals sometimes
<br />wetted before swallowing (Peifer 1979, but see
<br />Bayer 1981a). Armoured fish taken ashore, then
<br />speared and shaken with beak to break or relax the
<br />spines (Forbes 1982, but see Bayer 1985a).
<br />DIET
<br />Major food items. Wide array of animals
<br />induding fish, insects, mammals, amphibians, and
<br />crustaceans (Willard 1977, Kushlan 1978, Peifer
<br />1979). Voles 24% to 40% of diet of nestlings in
<br />Idaho (Collazo 1979); also important to juvenile
<br />survival in British Columbia in winter (Butler
<br />1991).
<br />Quantitative analysis. Data scant, mostly from
<br />breeding season. Predominantly fish (Parker 1980,
<br />Quinney and Smith 1979, Parker 1980, Horn 1983,
<br />The Birds of North America, No. 25, 1992
<br />Butler 1991). Occasionally chokes to deathonlarge
<br />prey items (Wolf and Jones 1989).
<br />NUTRITION AND ENERGETICS
<br />Estimated mean (± SE) intake of metabolized
<br />energy per day by individual herons feeding on
<br />small fish during 4 breeding stages was:' egg-
<br />laying 1,163 kJ (± 555), incubation 1,197 kJ (± 194),
<br />small chicks 4,264 kJ (± 764) and large chicks 1,598
<br />kJ (±`151; Butler 1991).
<br />DRINKING, PELLET CASTING, AND DEFECATION
<br />Water probably from diet. Casts pellets of
<br />mammal hair. Bones digested. Territorial herons
<br />depart from foraging sites to defecate more often
<br />than nonterritorial herons (Bayer 1980).
<br />FOOD SELECTION AND STORAGE
<br />Few data; fish about 5 to 30 art long, occasionally
<br />longer (Willard 1977).
<br />SOUNDS
<br />VOCALIZATIONS
<br />Mostly silent except at breeding colonies and
<br />when disturbed on foraging grounds. Geographic
<br />variation unknown. Calls show much variability
<br />and intergrade (Bayer 1984a).
<br />Vocal array. Bayer (1984a) lists 7 calls at
<br />breeding colonies: Frawnk call: rapid squawk,
<br />kt
<br />average duration of 19.7 s, given day
<br />when alarmed or when aggressive toward
<br />conspecifics; it may account for the local name
<br />"Crank" given to this species along the New
<br />England coast. Go -go-go call: a series of ducks
<br />given at the foraging site and breeding colony and
<br />often answered with same. The awk call: a scream
<br />lasting an average of 2.3 s, given mostly inbreeding
<br />colonies. The goon call resembles the bleat of a calf;
<br />uttered at the end of the "full forward" display
<br />(see Fig. 2a). Theee call: divided into two segments,
<br />uttered day and night mostly while flying. The
<br />roh- roh -roh call: a series of squawks uttered
<br />spontaneously for about 3.6 s by herons on the
<br />feeding grounds; also arrival at nests is often
<br />preceded by this call. Perhaps advertises territorial
<br />ownership on the foraging ground (Bayer 1984a)
<br />and mate recognition at nest (Mock 1976).
<br />NONVOCAL SOUNDS
<br />Loud bill snap, part of sexual display (see
<br />Behavior: sexual). Males snap bills most often
<br />when unmated and defending a nest site; also
<br />during bachelor stage when displaying toward
<br />females (Mock 1979); also once pairs form, but less
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