The little blue heron (Egretta caerulea) is unique amongst herons as it is the only species with two distinct colour morphs for mature and immature birds, with the adult bird being mostly slate-blue and the immature almost entirely bold white (3)(4). A medium-sized heron with a long neck and a thin, pointed, slightly downward-curving bill (2)(5)(6), the adult little blue heron also has a purplish to maroon-brown head and neck and a small white patch on the throat and upper-neck (3). During the breeding season, the head becomes more dark grey in colour, while the bill becomes more heavily black-tipped and the normally greyish-green legs turn to black (3)(5). Long, tapering, conspicuous feathers also develop on the crest and back of breeding birds (3). The male and female adult little blue heron are similar in appearance, but the juvenile is markedly different, with yellowish-green legs and mostly white plumage except for pale slate-grey primary feathers(3)(5)(6). The immature bird starts to develop adult plumage during its first spring when it becomes mottled blue and white, such that it has the appearance of tie-dye (3)(5). The little blue heron is rather secretive and typically forages in a slow, deliberate fashion. While at rest, it coils its neck in a characteristic S-shape (3)(7).
Walking slowly through shallow water with the neck and head held close to the surface, the little blue heron periodically stops and stands still to search for its prey, before thrusting its pincer-like bill into the water and grabbing its target (3)(6)(8). The little blue heron feeds mainly on a diet of fish and crustaceans, but this versatile predator may also consume a variety of frogs, tadpoles, insects, snakes, lizards and small mammals, often moving onto land to feed in grassy meadows (8). Juvenile little blue herons regularly forage in the company of the snowy egret (Egretta thula) as they tend to catch more fish when amongst groups of this bird than when foraging alone. This unusual feeding strategy is thought to increase the juvenile bird’s chance of survival at a time when it is most vulnerable to starvation and may also explain why it has white plumage. Similarly, the white plumage may allow juvenile birds to integrate into flocks of other white-coloured herons and so gain a greater degree of protection against predators (4).
Although largely solitary for much of the year, during the breeding season the little blue heron is gregarious and nests in groups at the edge of other heron colonies (3)(5)(6). Unpaired males typically arrive at the breeding colonies first so as to establish a small territory around a fork in a tree, which will eventually become the nesting site. The male little blue heron then displays to spectating females with advertising ‘stretch displays’, which involve the crest and neck feathers being erected, the bill pointed upwards and a small lunge into the air. Once paired up, partners reinforce the breeding bond by bill-nibbling and assuming a side-by-side posture. The male little blue heron may have already constructed a crude nest platform, but the female adds to this with material collected by the male (3). Between 3 and 5 eggs are laid and are incubated for approximately 20 to 23 days. The young fledge from the nest after 42 to 49 days, but may continue to be fed by the adult birds for several days until they become fully independent (2)(6).
Occurring throughout much of the Americas, the little blue heron ranges from southern California and the south-eastern US south to Peru and Central Brazil. Outside of the breeding season it may wander as far north as Canada (3)(5)(8).
The little blue heron nests in coastal areas, where it builds its nest in shrubs and small trees in standing water or on elevated sites on islands. It typically forages in freshwater lakes, marshes, swamps, streams, rivers and ponds, or in artificial wetlands such as canals, ditches or flooded agricultural fields. Outside of the breeding season, the little blue heron is also frequently found in mangroves, lagoons, mudflats and savannas and may even travel further inland to regions of higher elevation (3)(5).
Once hunted for its feathers, which were used in the hat-making trade, today the greatest threat to the little blue heron is the loss and degradation of freshwater wetlands. The species’ nesting sites are generally well protected, but its foraging sites are often subject to drainage and pollution, which can limit the amount of food available to this species (3)(5)(6). In parts of its range, the little blue heron is also threatened by persecution due to its habit of foraging at fish-rearing facilities, and by contamination from pesticides and heavy metals, such as mercury, as it forages in agricultural fields. In addition, there is much debate as to whether the little blue heron is threatened by competition with the exotic cattle egret (Bubulcus ibis). This bird, which arrived in North America in the early nineteenth century with the expansion of agriculture and cattle farming, is more aggressive than other herons and is said to out-compete the little blue heron for food, although the severity of this threat is currently unknown (3)(5).
The killing, collecting or harassment of the little blue heron, including its nests and eggs, is currently prohibited in the U.S. by the Migratory Bird Treaty Act, although some states permit fish-rearing facilities to shoot this species. There are also some special regulations in place that prevent trespassers from accessing little blue heron breeding colonies (6). However, the continuing decline of little blue heron populations suggests that, despite the protection of colony sites, the preservation of important foraging habitat has not been successful. Therefore, a conservation priority for the little blue heron is the adequate protection of its most important foraging sites, as well as the continued preservation of key nesting sites. These measures may prove more successful if accompanied by public environmental education programmes and the construction of artificial nesting islands. Further studies are also required into the possible adverse effects of the cattle egret and pollution on the little blue heron (3)(5).
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Diverse group of animals with jointed limbs and a hard chitinous exoskeleton characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps and barnacles.
To keep eggs warm so that development is possible.
One of two or more distinct types of a given species, often distinct colour forms, which occur in the same population at the same time (that is, are not geographical or seasonal variations).
In birds, the main flight feathers projecting along the outer edge of the wing.
An area occupied and defended by an animal, a pair of animals or a colony.
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