Species Description: Egretta tricolor is a medium sized, long necked wading bird of the Order Ciconiiformes (herons and storks). In this species, sexes are similar in appearance. Overall body color is gray along the neck, back and wings; and white along the foreneck and much of the ventral area. The legs are greenish or yellow in color, and the black-tipped bill can range from shades of blue to yellow.
Regional Occurrence: E. tricolor occurs along the Atlantic coast from Massachusetts south through Florida, the Gulf of Mexico and much of South America.
IRL Distribution: Occurs throughout the Indian River Lagoon.
Age, Size, Lifespan: Tricolored herons attain a maximum size of approximately 22 inches, with a wingspan of 38 inches.
Abundance: Tricolored herons are common inhabitants of the Indian River Lagoon.
Reproduction: Tricolored herons begin nesting in early to mid-March in Florida (Smith and Collopy 1995). There is a positive correlation between receding water levels in Lake Okeechobee and nesting sites chosen by tricolored herons. It is believed that areas with receding water levels are preferred because they have the effect of concentrating prey in a smaller area, thus making it simpler to feed nestlings (Smith and Collopy 1995). Between 3 - 7 eggs are laid per clutch. One brood is raised each year; however, should eggs be abandoned or destroyed, a replacement clutch can be laid.
Predation and disturbance rates determine nest success in all wading bird species. Cold weather events are particularly detrimental to nest success in many species. Additionally, in Florida, the active management of water levels in wetland areas such as Lake Okeechobee may also contribute to nest success (Smith and Collopy 1995). It has been suggested that in order to enhance nest success and later fledgling success, water levels in managed wetlands should be maintained at low or receding levels throughout the December to March nesting season. Low water levels help to concentrate prey in a small area, thereby making it simpler for parent birds to feed nestlings. It also contributes to the foraging success of fledglings (Smith and Collopy 1995).
Embryology: Rodgers (1980), in a study conducted in Hillsborough County, Florida, observed a mean clutch size in tricolored herons of 2.79 eggs per nest, with a 96% hatching rate. Approximately 70.5% of nestlings survived from birth to 2 weeks of age.
Eggs are incubated for approximately 21 - 25 days. As in all heron and egret chicks, hatching is asynchronous, and occurs over several days. The first chick to hatch quickly gains experience at food handling and aggressive interactions with siblings, so is often able to outcompete its siblings. Thus, growth rates are unequal among nestmates. In one California study, it was observed that as chicks age, predation gives way to starvation as the primary cause of death (Alfaro and Russi 1989).
Young fledge after approximately 35 days.
Trophic Mode: Strong et al. (1997) observed tricolored herons to be solitary feeders, with only 3% of birds associating with mixed flocks of other wading birds. Tricolored heron in Florida waters primarily consume snook, followed by guppies and gobies (Miranda and Collozo 1997). E. tricolor in the Florida Everglades and Lake Okeechobee areas show low diet diversity compared to other heron species, with a preference for fish of intermediate size (Smith 1997). Kent (1986) observed tricolored herons capturing, but always releasing, small crabs.
Food offered to nestlings includes approximately 27 different species, though the most important items in the diet were sailfin mollies, followed by mosquitofish, killifish, and golden topminnows (Smith 1997).
Smith (1997) observed that while other heron and egret species such as the great blue heron and the little blue heron will alter their diets in response to changing hydrological and habitat conditions, tricolored herons and snowy egrets do not. Rather, they change their foraging habitats and feeding strategies in order to continue to encounter preferred prey items.
In foraging efficiency, the tricolored heron falls last behind the little blue heron and the snowy egret in terms of striking efficiency (i.e., the percentage of strikes that result in capture and ingestion of prey). However, in terms of food intake per minute (g/min), the tricolored heron outcompetes both the little blue heron and the snowy egret. Of the 3 species, Kent's (1987) study estimated that the tricolored heron, due to its preference for somewhat larger sized prey, obtained its daily energy requirement fastest. In terms of caloric intake per minute, the little blue heron was required to forage 0.6 times as long as the tricolored heron, while the snowy egret required twice as much time as the tricolored heron to take in the same amount of energy. Willard (1977) observed the primary foraging strategies of tricolored herons to be: 1) standing still on banks waiting for prey to swim by, 2) wading slowly, and 3) active disturb-and-chase behavior. Tricolored herons achieve the greatest striking efficiency with less active behaviors such as wading slowly (Kent 1986); however, this highly efficient behavior is used equally as often as inefficient disturb-and-chase strategies (Willard 1977; Kent 1987). As evidenced by these foraging behaviors, tricolored herons may not have the goal of achieving maximum feeding efficiency, but rather try to maximize their energy intake through the infrequent capture and ingestion of high quality prey (Kent 1987).
Competitors: E. tricolor competes with other species of wading birds for food resources and nesting space. However, habitat partitioning and resource partitioning among species reduces direct competition such that species can coexist.
Habitats: The tricolored heron shows significant habitat overlap with other species of wading birds, particularly the great blue heron, the little blue heron, and the snowy egret (Kent 1986; Willard 1977). However, it appears to prefer small pools over lakes and bays (Chavez-Ramirez and Slack 1995). Strong et al. (1997) observed that tricolored herons were consistent in their choice of habitat among both wet and dry years, tending to avoid inland marshes and sloughs in favor of mangrove habitats and coastal marshes. When inhabiting freshwater areas such as Lake Okeechobee, Florida, tricolored herons were particularly attracted to Hydrilla and lotus (Nelumbo lutea) plants, using the leaves of the lotus for support while fishing among Hydrilla mats (Smith and Collopy 1995).
Associated Species: Though tending to be somewhat solitary in its feeding behavior, the tricolored heron can often be found in association with other medium sized wading birds.
Special Status: E. tricolor is listed as a Species of Special Concern (SSC) in Florida, but is not federally listed as threatened or endangered.
Benefit in IRL: The environmental sensitivity of wading birds, coupled with the relative ease of assessing their numbers, makes them attractive as biological indicators of ecosystem health and habitat quality (Custer and Osborn 1977; Powell and Powell 1986; Powell et al. 1989).
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Chavez-Ramirez F, Slack RD. 1995. Differential use of coastal marsh habitats by nonbreeding wading birds. Colonial Waterbirds 18: 166-171.
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Smith JP, Collopy MW. 1995. Colony turnover, nest success and productivity, and causes of nest failure among wading birds (Ciconiiformes) at Lake Okeechobee, Florida (1989-1992). Archiv for Hydrobiologie, Adv Limnol 45: 287-316.
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