Tricolored Heron Habitat Model
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Draft Date:
June 2002

Species:
Tricolored heron, Egretta tricolor

Use of Study Area Resources:
Reproduction. Tricolored herons breed along and somewhat inland of the U.S. Gulf Coast, all of Florida, and along the Atlantic coast into New England.  They also breed along the both coasts of Mexico, Central and South America, and the western Caribbean (Frederick 1997). Tricolored herons winter in coastal southern California, Mexico, and most of Central America, and the Gulf and Atlantic coasts up through the Carolinas (Frederick 1997). They undertake moderate post-nesting dispersal, including a general northward and interior movement before a southward winter migration (Frederick 1997, Palmer 1961).  On the Atlantic coast birds may travel north into Canada, returning when weather becomes cold and prey scarce (late September and October).  This species expanded its range into New England prior to the 1970's, but breeding still is uncommon in the Northeast (Andrews 1990).

Habitat Requirements:
Cover. Tricolored herons breed primarily in coastal wetlands (Frederick 1997), such as salt marshes, estuarine shallows, tidal flats, and river deltas, but also may use freshwater areas such as ponds and marshes.  They often nest in mixed colonies with other waterbirds. Nests generally are constructed in trees and shrubs on higher ground surrounded by open water or flooded marsh (Frederick 1997), but tall reeds, grasses, or the ground may be used (Spendelow and Patton 1988).

Nest substrates in the Northeast may be oak, maple, holly, willow, or waxmyrtle (Frederick 1997); where woody plants are lacking will use rushes or cane (Palmer 1961). Over time, the vegetation may be damaged by nest building activities and excrement, with the result that the birds move or colonies are abandoned until the site regenerates.

Foraging. Tricolored herons "...sometimes feed in freshwater marshes, but essentially are birds of brackish and saltwater areas." (Spendelow and Patton 1988). They feed mostly on small freshwater and estuarine fishes (> 90% of the diet), but will consume crustaceans, frogs, and insects when abundant (Frederick 1997, Smith 1997). Foraging typically is in shallow, sparsely vegetated estuarine waters (Frederick 1997).  

During the breeding season the nesting birds require adequate forage within a suitable flight distance.  Average foraging travel distances were about 6 km, with maximum of 28 km from lower Everglades breeding colonies (Bancroft et al. 1990 in Frederick 1997), and 2.4 km, with a maximum of 22 km at Lake Okeechobee (Smith 1995).

Habitat Mapping:
Data Sources: Data on nesting colonies were obtained from the Maine Department of Inland Fisheries and Wildlife (MDIF&W) Seabird Nesting Island databases, from Andrews 1990, and from Massachusetts Fisheries and Wildlife (Brad Blodgett).  Pierson et al. (1996) gave narrative descriptions of foraging sites frequented by tricolored herons in Maine.

All upland areas of active (most recent survey, at least since 1984) colonies were regarded as optimal nesting habitat, and so scored 1.0. SItes used since 1970,  but not in most recent surveys, were scored 0.8. Foraging areas were mapped by selecting fresh and marine wetlands bounded by any USDA Forest Service Ecological subunits (Keys et al. 1995) within 30 km of active nesting colonies, or otherwise having regular documented use, indicating value for dispersing birds. Foraging scores range from 0.9, as optimal, to 0.5, as suitable, allowing foraging and nesting areas to be distinguished the single (combined) output grid. Foraging areas within 10 km of active nesting colonies were scored at the nominal values (see table, below); those more distant from nesting colonies were scored at half those values.

NWI Designations (wetlands only)	Cover Types	Cover Suitability (0 - 1 scale)
	Upland deciduous forest
	Upland coniferous forest
	Upland mixed forest
	Grassland
	Upland scrub/shrub
	Cultivated
	Developed
	Bare ground
PEM, L2EM	Lake/pond, emergent vegetation	0.5
PFOcon	Palustrine forest, conifer
PFOdec	Palustrine forest, deciduous
PSSdec	Palustrine scrub shrub, deciduous
PSScon	Palustrine scrub shrub, conifer
PAB, L2AB	Lake/pond, aquatic vegetation	0.5
L1UB, PUB	Lake/pond, unconsolidated bottom
L2US	Lake, unconsolidated shore	0.5
L2RS	Lake, rocky shore	0.5
R1UB	Riverine subtidal unconsolidated
Rper	Riverine perennial	0.5
E1AB	Estuarine subtidal vegetated
E1UB	Estuarine subtidal unconsolidated bottom
E2AB	Estuarine intertidal algae	0.9
E2EM	Estuarine intertidal emergent	0.9
E2RS, R1RS	Estuarine, tidal river rocky shore	0.9
E2SS	Estuarine intertidal shrub	0.7
E2US/R1US	Estuarine, Riverine intertidal unconsolidated shore	0.9
M1AB	Marine subtidal vegetated
M1UB	Marine subtidal unconsolidated bottom
M2AB	Marine intertidal algae	0.7
M2RS	Marine intertidal rocky shore	0.7
M2US	Marine intertidal unconsolidated shore	0.7
NOTES

Sources:

Andrews, R. 1990. Coastal Waterbird Colonies Maine to Virginia 1984-85. U.S. Fish and Wildlife Service. 429 pp.

Hafner, H. 1997. Ecology of wading birds. Colonial Waterbirds 20(1):115-120.

Frederick, P.C. 1997. Tricolored heron, Egretta tricolor. In A. Poole and F. Gill, (eds.) The Birds of North America, No. 306. The Academy of Natural Sciences, Philadelphia, and The American Ornithologists' Union, Washington, D.C.

Keys, J.E., Jr., J.C. Carpenter, S. Hooks, F. Koenig, W.H. McNab, W. Russell and W. Smith. 1995. Ecological units of the eastern United States - first approximation (map and booklet of map unit tables), USDA Forest Service. Atlanta, GA.

Palmer, R.S. 1961. Handbook of North American Birds; Vol. 1. Yale University Press, New Haven CT. 567 pp.

Pierson, E.C., J E. Pierson and P.D. Vickery. 1996. A Birders Guide to Maine. Down East Books, Camden, ME.

Smith, J.P. 1995. Foraging flights and habitat use of nesting wading birds (Ciconiiformes) at Lake Okeechobee, Florida. Colonial Waterbirds 18(2): 139-158.

Smith, J.P. 1997. Nesting season food habits of 4 species of herons and egrets at Lake Okeechobee, Florida. Colonial Waterbirds 20(2): 198-220.

Spendelow, J.A. and S.R. Patton. 1988. National Atlas of Coastal Waterbird Colonies in the Coterminus United States: 1976-82. U.S. Fish and Wildlife Service Biol. Report 88(5). 326 pp.

Tyler, H.R. 1977. Wading birds in Maine and their relevance to the Critical Areas Program. Planning Rept. No. 26. 51 pp.