Species Description: Egretta caerulea is a medium sized, long-necked wading bird of the Order Ciconiiformes (herons and storks). Both sexes are similar in appearance, with deep blue-gray plumage, dull green legs, and a black-tipped bill. Head coloration can become chestnut brown during the breeding season.
Regional Occurrence: In the United States, E. caerulea occurs as far inland as Oklahoma. Coastally, it ranges from New York to Florida. Its range also includes the Gulf of Mexico, Central America and much of South America.
IRL Distribution: E. caerulea occurs throughout the Indian River Lagoon.
Age, Size, Lifespan: The little blue heron attains a height of 22 inches, with a wingspan of 41 inches.
Abundance: E. caerulea can be common in areas throughout its range.
Reproduction: Like the great blue heron (Ardea herodias), the little blue heron tends to form monospecific breeding colonies that are often located at the fringes of a mixed heron colony. This differs from most other medium sized wading birds such as the snowy egret (Egretta thula) and the white ibis (Eudocimus albus) which breed in mixed colonies (Maxwell and Kale 1997). Between 3 - 5 eggs are laid per clutch. One brood is raised each year; however, should the first nest be destroyed, a replacement clutch can be laid (Ehrlich et al. 1988). The nesting period for this species as observed in Lake Okeechobee, Florida begins in mid-March and April (Smith 1997).
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: Incubation time is approximately 20 - 23 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 42 - 49 days (Ehrlich et al. 1988).
Temperature: E. caerulea is eurythermal. On the east coast, little blue herons overwinter from New Jersey south to the Gulf of Mexico and South America (Farrand 1988). However, they can be cold sensitive during the breeding season, with spring cold events linked to nest failures at some sites (Smith and Collopy 1995).
Trophic mode: The little blue heron feeds by keeping its bill close to the surface of the water as it wades and peers around vegetation in search of prey. It apparently utilizes this slow wading behavior as its only method of feeding (Willard 1977; Kent 1987). Kent (1987) observed that less active feeding strategies such as slow wading tended to have increased striking efficiencies, the percentage of strikes that result in the capture and ingestion of prey. In the Kent (1987) study, little blue herons had better foraging efficiency than either the snowy egret or the tricolored heron. The tricolored heron was estimated to expend 1.5 times as much energy as the little blue heron in feeding, while the snowy egret expended approximately 2 times as much energy as the little blue heron. However, in terms of food intake per minute (g/min), the little blue heron falls between the tricolored heron and the snowy egret. Overall then, the little blue heron must forage approximately 0.6 times longer than the tricolored heron to obtain its daily energy requirement, while the snowy egret must forage twice as long.
In a Puerto Rican study (Miranda and Collozo 1997), E. caerulea adults were observed to feed solely on fiddler crabs (Uca spp). However, Smith (1997), in a study of wading birds in Lake Okeechobee and the Florida Everglades, found that E. caerulea feeds primarily on amphibians as well as on other crustaceans (i.e, shrimp, other crab species, etc.). Fish, when taken, tend to be larger than those taken by wading birds of similar size.
When environmental conditions change and begin to affect food supplies, the little blue heron responds by adjusting its diet to include alternate prey types. This differs from some other species of wading birds such as the snowy egret and tricolored heron which alter their feeding strategies and foraging habitat in order to continue to encounter preferred prey (Smith 1997).
Food offered to nestlings includes as many as 30 different species. Grass shrimp appear to be the primary nestling food, followed by mosquitofish, killifish, and the sailfin molly (Smith 1997).
Competitors: Other medium sized wading birds such as the snowy egret and tricolored heron and white ibis utilize similar habitats and food resources, but there is some evidence to suggest that resource partitioning among species minimizes direct competition (Smith 1997).
Habitats: In a study conducted in the Indian River Lagoon, around the vicinity of Vero Beach, Florida, Maxwell and Kale (1997) found that E. caerulea nested exclusively in black mangrove trees at the fringes of a mixed heron colony. In a Lake Okeechobee, Florida study by Smith and Collopy (1995), it was observed that little blue herons prefer to nest in lake or pond areas where spring water levels are low or receding. Reduced water levels in lakes and ponds helps concentrate prey, thus increasing nest success and the later foraging success of fledglings. Collopy and Smith (1995) have suggested this choice of breeding habitat has direct applications to wetland management around Lake Okeechobee. With the large numbers of wading birds nesting in this area, it could be most beneficial to bird populations for wetland managers to consider keeping lake levels low in the late winter or early spring months of the nesting season.
Associated Species: E. caerulea shares forging habitat with other wading birds of similar size such as the snowy egret and tricolored heron. Breeding habitat is generally unshared, with little blue herons initiating monospecific breeding colonies located along the fringe areas of mixed heron colonies.
Special Status: In Florida, listed as a species of species of special concern (SSC). It 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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