Little Blue Heron Habitat Model
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Little blue heron, Egretta caerulea
Use of Study Area Resources:
Reproduction, migration. Little blue herons breed within inland and coastal wetlands in the Gulf Coast and south-central states through Florida, Georgia, and the Carolinas. They also breed along the Pacific coast of Mexico and Central America, and the Gulf Coast of Mexico, the Caribbean, and the Atlantic coast as far north as Maine. Little blue herons winter in southern California, Florida, Central and South America (Rodgers and Smith 1995). Post-nesting dispersal is typically widespread, including a general northward and interior movement before a southward winter migration (Rodgers and Smith 1995). On the Atlantic coast birds travel as far north as New Brunswick and Nova Scotia, returning when weather becomes cold and prey scarce (late September and October). Nesting activities extended further north in Maine during the 1970's (Tyler 1977), but this species is 'relatively uncommon in the Northeast' (Andrews 1990).
Cover. Little blue herons feed in a variety of freshwater and estuarine covers (Rodgers and Smith 1995), such as marshes, swamps, streams, rivers, ponds, impoundments, flooded agriculture fields, estuarine shallows and tidal flats. They seem to prefer inland wetlands - ponds, freshwater marshes, and wet meadows - to coastal areas (Spendelow and Patton 1988). Little blue herons use same cover types during the breeding season and migration. They often nest in mixed colonies with other waterbirds. Nests generally are constructed in trees and shrubs standing in water, or on small islands of interior wetlands, swamps, ponds, lakes, or impoundments, or marine islands within range of foraging areas.
Nest substrates in the Northeast may be oak, holly, cattail or Phragmites, willow, or blueberry (Rodgers and Smith 1995). 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. Little blue herons feed on a wide variety of small freshwater and estuarine fishes, crustaceans; also frogs, and insects (Rodgers and Smith 1995). Smith (1997) observed that grass shrimp were more frequently fed to nestlings in Lake Okeechobee, Florida, than were fishes, in contrast to proportions fed by other nesting waders. This suggests that freshwater wetlands may be more suitable than estuarine wetlands for little blue herons, because the preferred invertebrate prey would have a lower salt content than is found in coastal invertebrates. This hypothesis is supported by a similar selection of prey for nestlings by white ibis in South Carolina (Bildstein 1997).
During the breeding season the nesting birds require adequate forage within a suitable flight distance. Erwin et al. (1987) and Erwin and Spendelow (1991) observed that distances were generally (50-70%) less than 6 km for several wader species, but up to 28 km; mean travel distances for 4 spp of egrets and herons "were all well below 5 km". Frederick and Collopy (1988) also found daily travel distances of Everglades birds to be 5 km or less, and Rodgers and Smith (1995) found that foraging generally took place within 7 km of freshwater interior colonies, and 10 km from marine colonies in Florida. Figures in Gibbs and Woodward (1984) for great blue herons in Maine had a mean of 6 km and a maximum of over 30 km. In the Mediterranean region the area and quality of wetlands appears to control the size and diversity of wading bird colonies; as the availability of freshwater habitat within 5 km falls below 800 ha, the colony size and species diversity declines significantly (Hafner 1997).
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 little blue 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.
|Cover Types||Cover Suitability
(0 - 1 scale)
|Upland deciduous forest|
|Upland coniferous forest|
|Upland mixed forest|
|PEM, L2EM||Lake/pond, emergent vegetation||0.9|
|PFOcon||Palustrine forest, conifer||0.9|
|PFOdec||Palustrine forest, deciduous||0.9|
|PSSdec||Palustrine scrub shrub, deciduous||0.9|
|PSScon||Palustrine scrub shrub, conifer||0.9|
|PAB, L2AB||Lake/pond, aquatic vegetation||0.9|
|L1UB, PUB||Lake/pond, unconsolidated bottom|
|L2US||Lake, unconsolidated shore||0.9|
|L2RS||Lake, rocky shore||0.9|
|R1UB||Riverine subtidal unconsolidated|
|E1AB||Estuarine subtidal vegetated|
|E1UB||Estuarine subtidal unconsolidated bottom|
|E2AB||Estuarine intertidal algae||0.7|
|E2EM||Estuarine intertidal emergent||0.7|
|E2RS, R1RS||Estuarine, tidal river rocky shore||0.7|
|E2SS||Estuarine intertidal shrub||0.7|
|E2US/R1US||Estuarine, Riverine intertidal unconsolidated shore||0.7|
|M1AB||Marine subtidal vegetated|
|M1UB||Marine subtidal unconsolidated bottom|
|M2AB||Marine intertidal algae||0.5|
|M2RS||Marine intertidal rocky shore||0.5|
|M2US||Marine intertidal unconsolidated shore||0.5|
Andrews, R. 1990. Coastal Waterbird Colonies Maine to Virginia 1984-85. U.S. Fish and Wildlife Service. 429 pp.
Bildstein, K.L. 1997. Wading-bird science: a guide for the twenty-first century. Colonial Waterbirds 20(1):138-142.
Erwin, M.E., J.E. Spendelow, P.H. Geissler and B.K. WIlliams. 1987. Relationships between nesting populations of wading birds and habitat features along the Atlantic coast. In W.R. Whitman and W.H. Meredith (eds): Waterfowl and wetlands symposium; proceedings of a symposium on waterfowl and wetland management in the coastal zone of the Atlantic flyway. Delaware Depart. of Nat. Res. and Environm. Control, Dover DE. 552 pp.
Erwin, M.E. and J.E. Spendelow. 1991. Colonial wading birds; herons and egrets. Pp. 19-1 through 19-14 in S.L. Funderburk, S.J. Jordan, J.A. Mihursky, and D. Riley (eds.) Habitat Requirements for Chesapeake Bay Living Resources. Habitat Objectives Workgroup, Chesapeake Bay Research Consortium, Inc. Solomons, MD.
Frederick, P.C. and M.W. Collopy. 1988. Reproductive ecology of wading birds in relation to water conditions in the Florida Everglades. Florida Coop. Fish and Wildl. Res. Unit, Sch. For. Res. and Conserv. Univ. of Florida. Tech Rept. No. 30.
Gibbs, J. and S. Woodward. 1984. Breeding colonies of great blue herons on Maine coastal islands. Maine Chapt. The Nature Conservancy, 1984.
Hafner, H. 1997. Ecology of wading birds. Colonial Waterbirds 20(1):115-120.
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.
Pierson, E.C., J E. Pierson and P.D. Vickery. 1996. A Birders Guide to Maine. Down East Books, Camden, ME.
Rodgers, J.A.,Jr. and H.T. Smith. 1995. Little blue heron, Egretta caerulea. In A. Poole and F. Gill, (eds.) The Birds of North America, No. 145. The Academy of Natural Sciences, Philadelphia, and The American Ornithologists' Union, Washington, D.C.
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.
Veit, R.R. and W.R. Petersen. 1993. Birds of Massachusetts. Massachusetts Audubon Society. 514 p.