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BIOLOGICAL AND ECOTOXICOLOGICAL CHARACTERISTICS OF TERRESTRIAL VERTEBRATE SPECIES RESIDING IN ESTUARIES

Tricolored Heron Tricolored Heron photo by Peter Osenton
(Photo by Peter Osenton)
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Biological Characteristics 

Species

Once called the Louisiana heron, Egretta tricolor is 63-76 cm in length. Males have an approximate mass of 415 grams and females 334 grams (Dunning, 1993). Its gray-blue plumage is offset by a conspicuous white belly and a white stripe that runs from the chin down the neck (Bull and Farrand, 1977; Hancock and Kushlan, 1984). During the non-breeding season the bill is yellow with a black tip, and the legs are yellow. When breeding, the bill turns bright blue (though the tip remains black) and the legs are bright pink (Hancock and Kushlan, 1984).

Status in Estuaries

This species typically breeds in colonies with other heron species and is generally found in brackish and salt water coastal areas, marshes, swamps, and mud flats (Bull and Farrand, 1977). Nests are close to or on the ground, preferably where tides are low (Hancock and Kushlan, 1984; Custer and Osborn, 1978). Typical clutch size is 3 or 4 pale bluish green eggs. Young are altricial (Ehrlich et al., 1988). The maximum age of a tricoloed heron recorded in nature 17 years.

Abundance and Range

The tricolored heron is found in North America, from Massachusetts southward to the Gulf Coast. The winter range extends from Virginia southward (Bull and Farrand, 1977). In the late 1970's, a total of 14,697 individuals were counted along the Atlantic Coast (Maine to Georgia), 13,644 along the Florida Coast, and 150,485 along the Gulf Coast (Spendelow and Patton, 1988). Less than 194,000 individuals are presently estimated in North America (NACWCP, 2001).

Site Fidelity

Dependent upon the regional availability of nesting sites and the consistency of food supplies from year to year, this species may exhibit site fidelity.

Ease of Census

This species is dark in color, and often stands motionless in grass pointing its bill upwards, making enumeration difficult (Hancock and Kushlan, 1984).

Feeding Habits

The tricolored heron forages by walking slowly or standing motionless in water and striking at prey. Its diet consists primarily of fish, but may include amphibians, insects, crustaceans and gastropods (Hancock and Kushlan, 1984). This species tends to feed within 2 km of its nest site (Custer and Osborn, 1978).


Tricolored Heron Contaminant Exposure Data

I.

Organochlorine Contaminants

1.

In 1970, five tricolored heron eggs were collected from various locations in Texas (King et al., 1978).  Mean contaminant concentrations were 6.50 mg/g wet weight ΣDDT (sum of DDD, DDE and DDT), 0.16 mg/g dieldrin, and 2.40 mg/g PCB.

2.

In 1970 and 1971, three tricolored herons were collected in Louisiana and Alabama (Ohlendorf et al., 1981). DDE in the carcass (excludes head, skin, feet, wing tips, liver, kidneys and gastrointestinal tract) ranged from 0.11- 3.0 mg/g wet weight. DDD was detected in only one carcass at 0.13 mg/g. DDT, dieldrin, heptachlor epoxide, oxychlordane, cis-chlordane, cis-nonachlor, trans-nonachlor, endrin, toxaphene, HCB and mirex were not detected. PCBs occurred at trace concentrations below the detection limit.

3.

Tricolored heron eggs were collected from National Wildlife Refuges located in the eastern half of the United States in 1972 and 1973 (Ohlendorf et al., 1978; 1979). Grouping samples geographically, DDE and PCBs were highest in the eggs collected from inland colonies, at overall means of 0.73 and 0.70 g/g wet weight, respectively. The greatest mean colony concentrations of DDE, (1.3 g/g), and PCBs (2.0 g/g) were found in Florida. Maximum concentrations detected in all individuals examined were 8.7 g/g DDE, 2.0 g/g DDT, 1.6 g/g dieldrin, 1.8 g/g mirex, and 12 g/g PCB. DDD, oxychlordane, toxaphene, heptachlor epoxide, cis-chlordane, and cis-nonachlor occurred at concentrations <1.0 g/g.

4.

Brains were collected from nestlings found dead at two sites in Florida between 1987-1991, and pooled samples were analyzed for several pesticides (Spalding et al., 1997).  Concentrations of HCB, oxychlordane, heptachlor epoxide, and trans-nonachlor were below detection limits. Mean DDE concentrations ranged from 0.01-0.07 g/g.

5.

In 1993, eggs (N=4) were collected from the National Audubon Sanctuary Islands of the Lower Laguna Madre, Texas (Mora, 1996a). Total PCB concentrations in these eggs averaged 0.071 mg/g wet weight. PCB congeners detected at the highest concentration were 138, 153, and 110.

6.

In 1993-94, tricolor heron eggs (N=4) were collected from the National Audubon Sanctuary Islands of the Lower Laguna Madre, Texas (Mora, 1996b). Median (range) contaminant concentrations were 0.056 (0.042-2.16) mg/g wet weight DDE and 0.067 (0.038-0.109) mg/g PCBs.

II.

Cholinesterase-Inhibiting Pesticides

 

No direct exposure data available

III.

Trace Elements, Metals, and Metalloids

1.

From 1974 to 1976, three tricolored herons were collected from Brunswick, Georgia (Gardner et al. 1978). Mean Hg concentrations of 7.0 mg/g dry weight in muscle, of which 67% was MeHg, and 37 mg/g in liver, of which 20% was MeHg, were found.

2.

In 1977, a tricolored heron was collected from the Brunswick Estuary in Georgia (Odom, unpublished). Mercury was detected at concentrations of 12.4 mg/g in the liver and 2.85 mg/g in the breast muscle. Another heron collected from the Brunswick Estuary in 1980 had 2.84 mg/g of Hg in the liver and 1.96 mg/g in the breast muscle (Odom, unpublished).

3.

In 1979, tricolored heron eggs, downy young, prefledglings and adults were collected at two locations on the Texas Gulf Coast (Red Fish Island and South Deer Island) (Cheney et al., 1981). Lead was detected at a mean level of 0.18 mg/g wet weight in the eggshell and 0.03 mg/g in the egg contents. Lead in tissues (brain, bone, heart, kidney, liver, and muscle) was highest in the adults, reaching a mean of 3.56 mg/g in the bone. Mean Cd concentrations were 0.003 mg/g in eggshells and 0.004 mg/g in egg contents. In tissue, mean Cd levels tended to be similar between ages and tissues (0.015-0.033 mg/g), except in the adult liver (0.078 mg/g) and kidney (0.823 mg/g).

4.

In 1983, tissue samples were collected from ten tricolored heron chicks nesting in South Carolina (White and Geitner, 1996). Lead in the liver was <1.7 mg/g wet weight, and Hg in the liver <0.18 mg/g. In the kidney, Se ranged from 1.0 to 1.5 mg/g, and Cd was not detected.

5.

Livers were collected from nestlings found dead at two sites in Florida between 1987-1991 (Spalding et al., 1997).  Mean concentrations of Pb, Cu, and Cd ranged from 0.20-1.4, 12-23, and 0.15-0.22 g/g wet weight, respectively.

6.

Nestlings, fledglings, and adults found dead were collected from four areas in south Florida between 1987-1991 and analyzed for hepatic Hg (Sundlof et al., 1994). Mean Hg concentrations were 0.57, 0.32, and 1.93 g/g wet weight  at Lake Okeechobee, the Everglades, and eastern Florida Bay, respectively, and below detection at Big Cypress National Preserve.  Mean Hg concentration ranged from 0.73-0.74 g/g in nestlings and was 0.67 g/g in fledglings.

7.

In 1993-94, four tricolored heron eggs were collected from the National Audubon Sanctuary Islands of the Lower Laguna Madre, Texas (Mora, 1996b). Median (range) metal concentrations (mg/g wet weight) were: 0.14 (0.03-0.20) Hg, 0.28 (0.19-0.59) Se, 0.96 (0.36-1.16) B, 0.11 (0.09-0.31) Cr, 0.92 (0.87-1.06) Cu, 16.4 (13.3-20.2) Fe, 114 (104-121) Mg, 0.35 (0.25-0.56) Mn, 1.14 (0.91-1.48) Sr, and 9.2 (8.4-10.9) Zn.

IV.

Petroleum

 

No residue data available 


Tricolored Heron Contaminant Response Data

I.

Organochlorine Contaminants

1.

To determine average shell thickness, 58 heron eggs were collected from Texas in 1970 (King et al., 1978). There was a significant 5% decrease in shell thickness between eggs collected in 1970 and the thickness of 31 eggs collected prior to 1943.

2.

No statistically significant difference in eggshell thickness was found between tricolored heron eggs collected from various National Wildlife Refuges in 1972 and 1973 and those collected prior to 1947 (Ohlendorf et al., 1978; 1979).

II.

Cholinesterase-Inhibiting Pesticides

 

No response data available

III.

Trace Elements, Metals, and Metalloids

 

No response data available

IV.

Petroleum

1.

Fifty-nine eggs were treated with 20 mL of number 2 fuel oil and then incubated for five days (White et al., 1979). Following incubation, 61% of the oil-treated embryos died. This was a significant increase over the control group in which none of the embryos died.

2.

Compared to untreated controls, significantly more tricolored heron embryos died when eggs were treated with 10 mL of 4-week-old weathered oil (Macko and King, 1980). 


References for Tricolored Heron

Bull, J. and J. Farrand, Jr. 1977. The Audubon Society Field Guide to North American Birds. Alfred A. Knopf, New York.

Cheney, M.A., C.S. Hacker, and G.D. Schroder. 1981. Bioaccumulation of lead and cadmium in the Louisiana heron (Hydranassa tricolor) and the cattle egret (Bubulcus ibis). Ecotoxicol. Environ. Safety 5:211-24.

Custer, T.W. and R.G. Osborn. 1978. Feeding habitat use by colonially-breeding herons, egrets, and ibises in North Carolina. Auk 95:733-743.

Dunning, Jr., J.B., ed. 1993. CRC Handbook of Avian Body Masses. CRC Press, Ann Arbor. 371 pp.

Ehrlich, P.R., D.S. Dobkin, and D. Wheye. 1988. The Birder's Handbook. Simon & Schuster, New York. 785 pp.

Gardner, W.S., D.R. Kendall, R.R. Odom, H.L. Windom, and J.A. Stephens. 1978. The distribution of methyl mercury in a contaminated salt marsh ecosystem. Environ. Pollut. 15:243-251.

Hancock, J. and J. Kushlan. 1984. The Herons Handbook. Harper and Row Publishers, New York. 288 pp.

King, K.A., E.L. Flickinger, and H.H. Hildebrand. 1978. Shell thinning and pesticide residues in Texas aquatic bird eggs, 1970. Pestic. Monitor. J. 12:16-21.

Macko, S.A. and S.M. King. 1980. Weathered oil: effect on hatchability of heron and gull eggs. Bull. Environ. Contam. Toxicol. 25:316

Mora, M.A. 1996a. Congener-specific polychlorinated biphenyl patterns in eggs of aquatic birds from the lower Laguna Madre, Texas. Environ. Toxicol. Chem. 15:1003-1010.

Mora, M.A. 1996b. Organochlorines and trace elements in four colonial waterbird species nesting in the lower Laguna Madre, Texas. Arch. Environ. Contam. Toxicol. 31:533-537.

NACWCP.  2001.  Review Draft IINorth American Waterbird Conservation Plan. Volume One: Seabirds and Colonial Waterbirds, 23 October 2001, Waterbird Conservation Steering Committee, Washington DC (www.nacwcp.org/).

Odom, R.R. 1978. Statewide wildlife investigations: Mercury contamination studies. Georgia Game and Fish Division. 15 pp.

Odom, R.R. 1981. Statewide wildlife investigations: Mercury contamination studies. Georgia Game and Fish Division. 17 pp.

Ohlendorf, H.M., E.E. Klaas, and T.E. Kaiser. 1978. Organochlorine residues and eggshell thinning in anhingas and waders. Proc. Conf. Colon. Waterbird Group 3:185-195.

Ohlendorf, H.M., E.E. Klaas, and T.E. Kaiser. 1979. Environmental pollutants and eggshell thickness: Anhingas and wading birds in the eastern United States. Special Scientific Report--Wildlife No. 216. U.S. Department of the Interior, Fish and Wildlife Service, Washington, D.C.

Ohlendorf, H.M., D.M. Swineford, and L.N. Locke. 1981. Organochlorine residues and mortality of herons. Pest. Monitor. J. 14:125-135.

Spalding, M.G., C.K. Steible, S.F. Sundlof, and D.J. Forrester.  1997.  Metal and organochlorine contaminants in tissues of nestling wading birds (Ciconiiformes) from southern Florida. Fla. Field Nat. 25:42-50.

Spendelow, J.A. and S.R. Patton. 1988. National atlas of coastal waterbird colonies in the contiguous United States: 1976-82. U.S. Fish Wildl. Serv. Biol. Rep. 88. 326 pp.

Sundlof, S.F., M.G. Spalding, J.D. Wentworth, and C.K. Steible.  1994.  Mercury in livers of wading birds (Ciconiiformes) in Southern Florida. Arch. Environ. Contam. Toxicol. 27:299-305.

White, D.H., K.A. King, and N.C. Coon. 1979. Effects of no. 2 fuel oil on hatchability of marine and estuarine bird eggs. Bull. Environ. Contam. Toxicol. 21:7-10.

White, D.H. and J.G.H. Geitner. 1996. Environmental contaminants and productivity in an extinct heronry at Charleston Harbor, South Carolina, U.S.A. 1984. Environ. Monitor. Assess. 40:137-141

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