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The American Ornithologists' Union
<br />ROBERT W. BUTLER
<br />Selection process. Males arrive in colony and
<br />settle on nests, where they court females
<br />(Brandman 1976, Mock 1976). Nest site fidelity
<br />weak; 13 of 14 marked individuals choose different
<br />nests the following yea (Simpson 1984), but fidelity
<br />to the choice of tree species within colonies can be
<br />strong (Kelsall and Simpson 1979). Some colonies
<br />have long histories of use: 71 yr in Stanley Park, BC
<br />(RWB), 37 yi•in Minnesota (M. Partch pers.comm.).
<br />Site characteristics. Nests mostly in trees, up to
<br />30 m or more above ground; usually lowland
<br />swamp or upland hardwood forest, islands, forest -
<br />bordered lakes and ponds, and riparian wood-
<br />lands, including conifers. Where trees not available,
<br />nests on ground (usually only on predator -free
<br />islands; Taverner 1926, Gill and Mewaldt 1979), in
<br />bullrushes, on shrubs (Behle 1958, Vermeer 1969),
<br />cacti (Rosenberg et al. 1991), sagebrush (Blus et al.
<br />1980), mangroves (generally islands; Powe111983),
<br />duck blinds (Palmer 1962), channel markers
<br />(Henny and Kurtz 1978, Blus et al. 1980), and
<br />artificial nest platforms (Sandilands 1980). Nests
<br />Figure 4.
<br />Most Great Blue
<br />Herons nest in
<br />colonies. Drawing
<br />by J. Zickefoose.
<br />with other species of herons (Custer et al. 1980),
<br />waterbirds, and even hawks, owls, and vultures
<br />(Mengel 1965, Ryser 1985, Simpson 1987). Nest
<br />density varies from 39 to 750 nests /ha in Oregon
<br />colonies (Bayer and McMahon 1981).
<br />NEST
<br />Sticks gathered from the ground, nearby trees,
<br />or unguarded nestsprimarily by males and placed
<br />on nest by females ( Cottrille and Cottrille 1958,
<br />Palmer 1962, Mock 1976). Nest built in 3 d to 2 wk,
<br />a platform of twigs with saucer - shaped interior
<br />lined with pine needles, moss, reeds, dry grass,
<br />mangrove leaves, or small twigs (Cottrille and
<br />Cottrille 1958, Palmer 1962, Pratt 1970). Four nests
<br />in British Columbia weighed 2,570, 2,600, 2,800
<br />and 4,820 g (Butler 1989). Material added
<br />throughout nesting period.
<br />Dimensions. Vary greatly, from flimsy new
<br />platforms of sticks just 0.5 m diameter to bulky
<br />older structures 0.9 to 1.2 m across (Andrle 1988);
<br />about 1 m deep in nests used several times.
<br />The Academy of Natural Sciences of Philadelphia
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