Great Blue Heron Ardea herodias
Version: 1.0 — Published March 4, 2020
Text last updated April 28, 2011
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Diet and Foraging
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Main Foods Taken
Mostly fish but also amphibians, invertebrates, reptiles, mammals, and birds (Palmer 1962a, Kushlan 1978b, Verbeek and Butler 1989, Butler 1995, Butler 1997). One report of scavenging carrion (Ritzi and Ritzi 2005).
Microhabitat For Foraging
See Habitat. The different foraging microhabitats of Great Blue Herons are best explained by individual ability. In British Columbia, juveniles forage in grasslands, adult females in estuarine marshes and intertidal beaches, and adult males along riverbanks (Butler 1997). Juveniles have poor foraging skills, which limits their use of beach habitats and ability to handle large fish (Gutsell 1995). The microhabitats of yearlings are poorly known, but include estuaries and beaches plus occasional visits to colony-sites (RWB). In the Pacific Northwest, herons occasionally can be found foraging from floating seaweed beds and wharves (Butler 1997).
Food Capture And Consumption
Forage singly, with conspecifics and other bird species. Behavior is flexible, and the diet varied. Reviews of Great Blue Heron foraging behavior have been published by Kushlan (1976, 1978) and Kelly et al. (2003).
Individuals hunt most often by slowly wading or standing in wait of prey in shallow water (Kushlan 1976a, Kushlan 1978b, Willard 1977, Hom 1983). Also dive feet first after prey (Forbes 1987), and hunt while floating (Jensen 1932), or from floating objects (Godin 1977). Kubisz (1989) reported a heron landing on the water to pick up a food item and then taking off from floating. Zickefoose and Davis (1998) reported a Great Blue Heron passively using bait (bread) to catch fish.
Wade more slowly and stop for longer periods than other herons (Willard 1977). Other behaviors of note reviewed by Kelly et al. (2003) include standing fly-catching, gleaning, wing flicking, hovering, and feeding while swimming. On tidal beaches, most foraging occurs on ebbing and low tides (Herbert 1996, Butler 1997). Often forage in flocks with other Great Blue Herons (Krebs 1974, Butler 1995), other ciconiiformes (Willard 1977, Kushlan 1978b), and Double-crested Cormorants (Phalacrocorax auritus (Butler 1997).
Can be found foraging at night and during the day (Black and Collopy 1983). Up to one third of total photoreceptors in ciconiiform eyes are rods, presumably an adaptation for night vision (Lish 1983). Prey are located by sight (Krebs and Partridge 1973) and are caught by a rapid forward thrust of the neck and head; then held between the mandibles before swallowing. Most prey are swallowed whole. Peifer (Peifer 1979) reported that small mammals sometimes are wetted before swallowing (but see Bayer [Bayer 1981a]). Armored fish generally are taken ashore, then speared and shaken with beak to break or relax the spines (Forbes 1982, but see Bayer [Bayer 1985c]).
Major Food Items
Wide array of animals including fish, insects, mammals, amphibians, birds and crustaceans (Willard 1977, Kushlan 1978b, Peifer 1979). Voles an important component nestling diet in Idaho (Collazo 1979); also important to juvenile survival in British Columbia during the winter (Butler 1991, 1995, 1997, Gutsell 1995).
Few data, most from the breeding season. In Nova Scotia, diet mostly flounders (98%, n=124 food items, Quinney and Smith 1979); in British Columbia, mostly sticklebacks, gunnels, sculpins and perch (Kelsall and Simpson 1979, Butler 1995, 1997); in California, sculpin, bass, perch, flounder and top smelt (Hom 1983). Voles accounted for 24-40% of the diet of nestlings in one Idaho study (Collazo 1979).
Food Selection and Storage
Few data are available. Great Blue Herons generally target fish about 5 to 30 cm long, occasionally longer (Willard 1977). Breeding herons in British Columbia ate disproportionately more shiner perch (Cymatogaster aggregata) and sculpins (Leptocottus armatus) than were estimated to be present (Butler 1995).
Nutrition and Energetics
The estimated mean (± SE) intake of metabolized energy per day by individual Great Blue Herons feeding on small fish during 4 breeding stages was: egg-laying 1,163 kJ (± 555), incubation 1,197 kJ (± 194), small chicks 4,264 kJ (± 764) and large chicks 1,598 kJ (± 151; Butler 1991). Hand reared captive chicks held in outdoor pens were estimated to consume 2,027 (± 25) kJ/d during the maximum growth period between 26-41 days of age, and 1545 (± 22) kJ/d by 50 days of age (Bennett et al. 1995). There was no significant difference in energy required by male and female chicks (Bennett et al. 1995).
Apparent metabolizable energy coefficients of prey include: mackerel (0.769± 0.063), trout (0.79± 0.029), and herring (0.621± 0.137; Bennett 1993).
Drinking, Pellet-Casting, and Defecation
Water intake for Great Blue Herons likely is gained from their diet. Mammal hair is cast in pellets, and bones are digested (RWB). Territorial herons depart from foraging sites to defecate more often than non-territorial herons (Bayer 1980b).