Conservation and Management

Shooting And Trapping

Probably not taken in large numbers for plume trade (late 1800s, early 1900s), and not hunted in North American range today. However, large increase in aquaculture in s.-central U.S. has led to large increase in permits to kill herons and other waders (Coon et al. 1996). In Guyana, eggs and young are often taken by humans, and adults are often hunted for food (Llowe-McConnell 1967).

Pesticides And Other Contaminants/Toxics

See Appendix 3 . Generally low values of pesticides and other contaminants in this species. Moderately high levels of DDE (1.3 ppm) and PCBs (2.0 ppm) found in eggs from St. Marks, Wakulla Co., FL (Ohlendorf et al. 1979); high levels of DDE and PCBs in eggs from Louisiana, although measurement in fat makes interpretation difficult (Faber and Hickey 1973). Spalding et al. (in press) found DDE at 0.01–0.07 ppm (wet weight in brain tissue) from 7 birds in Florida Everglades.

Mercury in livers of 12 nestlings from s. Florida averaged 0.72 ppm wet weight (range 0.12–4.96), with higher values from e. Florida Bay and central Everglades (Sundlof et al. 1994); liver mercury was inversely related to body fat. In central Everglades, mean of 1.4 µg/g lead (wet weight, liver tissue) is considered high, and in extreme cases (>2 µg/g, up to 6.3 µg/g in liver) may have contributed to death of nestlings (Spalding et al. in press).

Although this species does not appear to have been at high risk of contaminant accumulation during 1970s, most of the available contaminant values are now >20 yr old, and more recent surveys should be undertaken.

Collisions With Stationary/Moving Structures Or Objects

During 1,200 h of diurnal observations in Everglades, 0 of 567 Tricolored Herons were observed striking a high-voltage power line, although dead and wounded postfledging birds were sometimes found below it (PCF). These data suggest that collisions with power lines are rare in open habitat, although such collisions may increase when visibility is poor (fog, rain, crepuscular flight).

Degradation Of Habitat

Declining numbers in Everglades may be response to coastal degradation through reduced flow of fresh water to estuary (Frederick and Spalding 1994, McIvor et al. 1994, Ogden 1994), and this estuarine-dependent species is likely to be sensitive to reductions in estuarine productivity. This may be the most important conservation problem for the species. In Central and South America, losses of estuarine and marine swamps to commercial shrimp aquaculture and coastal development are likely to affect Tricolored Heron habitat (Bildstein 1990, Massey and Palacios 1994).

Disturbance At Nest And Roost Sites

Rodgers and Smith (1995) found that Tricolored Herons flushed from their nests at mean distance of 30 m when approached on foot, and 12 m when approached by canoe. Bratton (1990) reported that 19 of 20 foraging groups flushed in response to approach of boat with outboard motor to within 25 m. No changes in foraging behavior or location documented in response to intensity of human visitation at Ding Darling National Wildlife Refuge, Collier Co., FL (Klein et al. 1995). Chick growth retarded in proportion to frequency of researcher visits to nest (Portraj 1978, but see Frederick and Collopy 1989b). Overflights of F-16 jets at 150 m above ground level and up to 100 decibels had no measurable impact on reproductive behavior, success, or growth rates of chicks (Black et al. 1984). At least 2 colonies of free-ranging birds in Florida are situated at tourist attractions, despite daily close approach (within 1–10 m) by large numbers of tourists on boardwalks.

Direct Human/Research Impacts

Frederick and Collopy (1989b) found no differences in reproductive-success measures at a colony visited by researchers in an airboat at 4- and 8-d intervals in Everglades, although researcher visitation may affect nestling growth (Portraj 1978). American Crows may be attracted to disturbance caused by researchers, resulting in egg predation and consequent frequent nest failure and reduced clutch size of Tricolored Herons (Bent 1926, Bancroft et al. 1990).

Conservation Status

Classified as Migratory Bird (U.S.) and Species of Special Concern (Florida and Massachusetts). Declining rapidly in Florida, and perhaps elsewhere in se. U.S. Population probably stable on Yucatán Peninsula (Lopez-Ornat and Ramo 1992); declining in Baja California (Massey and Palacios 1994). Little other information about status outside of U.S. Migratory patterns suggest that wetland conditions in Greater Antilles, Yucatán, and Central America are important to U.S. wintering populations.

Measures Proposed And Taken

Identification of unprotected habitat in Florida (Cox et al. 1994) is an important preliminary conservation strategy—one that should be undertaken in other states throughout range. This species may have been positively affected throughout Gulf and Atlantic coastal range by construction and maintenance of dredge material islands (Parnell et al. 1986), and of coastal impoundments and protected islands of the National Wildlife Refuge system. Islands provide protection from mammalian predators for both roosting and breeding birds (see Breeding: nest site, above). Wintering populations may benefit strongly from aquaculture activities in Louisiana. Since the apparent take of aquaculture organisms by herons is small and largely unharvestable, Fleury (1994) has suggested that animal control measures are not necessary for herons, egrets, and ibises. Rodgers and Smith (1995) recommended setback distances for humans walking or in boats of 88 m for colonies and roosts.

Effectiveness Of Measures

The large increase in range and local abundance during 1950–1978 (see Demography and populations: population status, and Distribution, above) and the large number of colonies on dredge material islands suggests that the latter have benefited the species (Ogden 1978). Similarly, the large increases recorded on CBCs in Louisiana is highly correlated with increased acreage of crayfish aquaculture (Fleury and Sherry 1994), indicating that crayfish aquaculture may benefit this species. Protection of colonies in Florida apparently has not stemmed population declines there (see Demography and populations: population status, above).