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The American Ornithologists' Union
<br />(Curry- Lindahl 1971), and genetically (Sheldon
<br />1987), suggesting that they constitute a single
<br />species. Because they do not overlap in distribution,
<br />however, these taxa are usually considered to be
<br />semispecies constituting a superspecies (e.g.,
<br />Hancock and Elliot 1978, Payne 1979). Such a
<br />classification permits each of the semispecies to be
<br />divided into subspecies.
<br />Hancock and Elliot (1978) divided Great Blue
<br />Heron into seven subspecies, wardii (se. North
<br />America),cognata (GalapagosIs.), treganzai (middle
<br />North America), hyperonca (w. U.S.), sanctilucae (s.
<br />California), and occidentalis (Florida and West
<br />Indies). They also suggested that two more
<br />subspecies might usefully be described for Central
<br />American and Carribean forms. In general, most
<br />researchers view occidentalis (Great White Heron)
<br />as a localized color morph, but Curry- Lindahl
<br />(1971) believed it differed from typical Great Blue
<br />Herons in its behavior, possibly enough to be a
<br />distinct species. Payne (1979) recognized four
<br />subspecies, fannini, herodias, cognata, and
<br />occidentalis. He noted that while southern birds are
<br />larger than northern birds, the eastern variation in
<br />size is clinal. Thus, a single subspecies (herodias)
<br />suffices for most of continental North America,
<br />with the exception of the northwest (fannini) and
<br />Florida ( occidentalis). This account treats occidentalis
<br />as a color morph /subspecies of A. herodias.
<br />MIGRATION
<br />NATURE OF MIGRATION IN THE SPECIES
<br />Migrates alone or in groups of 3 to 12,
<br />occasionally up to 100, day and night (Palmer
<br />1962). Some wander northward in summer to
<br />arctic Alaska, s. Yukon, s. Keewatin, n. Manitoba,
<br />n. Ontario and n. Quebec (Brock 1959, Godfrey
<br />1986). Southward migration from northern
<br />localities from mid -Sep to late Oct. General
<br />movement away from northern edge of breeding
<br />range for winter (Henny 1972), but some recorded
<br />on Christmas Bird Counts in Canada each year.
<br />Spring migrants return in early Feb to Illinois,
<br />Wisconsin, and central Minnesota (Palmer 1962);
<br />mid -Mar to Vermont (Laughlin and Kibbe 1985)
<br />and British Columbia Butler et al. 1986); late Mar
<br />to Kentucky (Mengel 1965), Iowa (Dinsmore et al.
<br />1984), and Oklahoma (Sutton 1967); early Apr to
<br />Nova Scotia (Tufts 1 %1), Ontario (Devitt 1967),
<br />and Alberta (Vermeer 1969). Also arrive Nova
<br />Scotia by Mar, Canadian Prairies and Maritimes in
<br />Apr and early May (Palmer 1962). More infor-
<br />mation on arrival and departure dates needed to
<br />establish migration chronology.
<br />ROBERT W. BUTLER
<br />TIMING AND ROUTES OF MIGRATION
<br />Little information available. Most probably
<br />winter along ice -free coastlines and watercourses.
<br />Recoveries of U.S. and Canadian herons banded
<br />as nestlings east of the Rockies and recovered
<br />before their first birthday suggest many winter
<br />along Caribbean shores (Byrd 1978). Christmas
<br />Bird Counts (CBC) show large numbers in se. U.S.
<br />(see Fig. 5). Pacific coast populations appear
<br />nonmigratory (Byrd 1978, Gill and Mewaldt 1979)
<br />but some post- breeding dispersal occurs (Pratt
<br />1970, Butler 1991). Large concentrations in Puget
<br />Sound, WA, and Strait of Georgia, BC.
<br />MIGRATORY BEHAVIOR
<br />No information.
<br />CONTROL AND PHYSIOLOGY OF MIGRATION
<br />No information:
<br />HABITAT
<br />BREEDING RANGE
<br />Widespread and remarkably adaptable. Feeds
<br />mostly in slow moving or calm freshwater, also
<br />along seacoasts. Occasionally in surf and fields.
<br />Nests in trees, bushes, on ground and artificial
<br />structures (see Breeding: nest site), usually near
<br />water; prefers vegetation on islands or in swamps,
<br />probably to avoid ground predators. Breeding at
<br />elevations up to 1,100 m in British Columbia
<br />(Campbell et al. 1990), 610 min Vermont (Laughlin
<br />and Kibbe 1985), and 1,500 min Panama (Hancock
<br />and Kushlan 1984). Along east coast of U.S., avoids
<br />nesting in marine habitats in New Hampshire and
<br />New York (Spendelow and Patton 1988), favoring
<br />inland sites; farther north and south, nests near
<br />fresh and salt water. Great White Heron found
<br />almost exclusively in shallow -water marine
<br />habitats, particularly tidal grass flats.
<br />SPRING AND FALL MIGRATION
<br />No information but probably similar to breeding
<br />season.
<br />WINTER RANGE
<br />Little information. In Oklahoma, avoids farm
<br />ponds with little emergent vegetation in favor of
<br />natural wetlands and riverbanks (Heitmeyer 1986).
<br />In British Columbia, flies to estuaries (adult
<br />females) and nearby grasslands (juveniles) in
<br />autumn and winter when high tides and declining
<br />fish populations make foraging unprofitable on
<br />beaches; some adult males spend fall and winter
<br />on territories along river banks (Butler 1991). Also
<br />The Academy of Natural Sciences of Philadelphia
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