Little Blue Heron

识别特征

Males and females have the same coloration. The adults are darkly colored, with purple-maroon heads and blue bodies. During the breeding season, their heads turn dark red. They have two-toned bills, which are a light blue at the base, with black tips. Their eyes are yellow and their legs are greenish. Juveniles are almost completely white, although the upper primaries are somewhat dark in color. Like adults, their bills are two-toned. Immature birds transitioning from the juvenile to adult phase have a combination of light and dark feathers. Both sexes are about 56–74 centimetres (22–29 in), with a wingspan of 100–105 centimetres (39–41 in). They weigh about 397 grams (14.0 oz).<p>The lores, which are normally a dull green become a shade of turquoise. They also develop long plumes on the crest and back, which can stretch 20–30 centimetres (7.9–11.8 in) past the tail. The legs and feet become black. The eggs are typically smooth, light blue, and unmarked. In size, they are about 31.7–43.2 millimetres (1.25–1.70 in), with a weight of around 23.1 grams (0.81 oz).

分类信息

The little blue heron is part of the family Ardeidae, a group whose members can be found throughout much of the world, including the Americas, Africa, Asia, and Oceania. It was first described as Ardea caerulea by Carl Linnaeus in his 10th edition of Systema Naturae. It is now a member of the genus Egretta. It may be closely related to the snowy egret, another member of its genus, which it greatly resembles when young. Variations of the name include Ardea coerulea, Florida caerulea, and Hydranassa caerulea.<p>Young birds found in a little blue heron nest in North Dakota, at a site heavily populated by cattle egrets (Bubulcus ibis), which displayed traits of both the former and latter, are believed to be an example of hybridization between the two species. Other species they are known to hybridize with include the tricolored heron, little egret, snowy egret, and black-crowned night heron. Of these four, only the black-crowned night heron is not a member of Egretta.

学名

Egretta caerulea

命名信息

(Linnaeus, 1758)

目

Pelecaniformes

科

Ardeidae

属

Egretta

分布与栖息地

Egretta caerulea can be found regularly in the United States, Mexico, Central America, northern South America (including Venezuela, Colombia, and Peru), and numerous Caribbean islands (including Cuba, Jamaica, and Hispaniola). They have been recorded as a vagrant (a species that appears far outside its natural range) in Greenland, Portugal, and South Africa. Whether or not their range is declining is unknown. In the United States, they can be found from Missouri to Virginia to Florida. They are more common in peninsular Florida than the Florida Panhandle. They can occasionally roam as far north as Canada.<p>Individuals in central Alabama tend to migrate towards South America and the Caribbean, while those from the Mississippi River west travel to Mexico and Central America. One study found that of seven migratory wading bird species, the little blue heron had the greatest mean dispersal distance, of 1,148 kilometres (713 mi).<p>Future climate change is projected to increase its overall range. If global warming continues at its current rate, by the year 2080, its summer range will have increased by 87%. Of its current range, it is expected to lose only 1%. These gains would spread its summer distribution well into more northern parts of the US, such as Michigan and Minnesota, and even into southern Canada.<p>The little blue heron can be found in freshwater and marine environments. These include mangrove forests, bogs, swamps, salt marshes, tidal flats, estuaries, streams, and flooded fields. They are usually found at low elevations, but can be seen at heights of 3,700 metres (12,100 ft) in the Andes.<p>In North America, they tend to favor freshwater habitats, while in the Caribbean, they are more often found in saltwater. Towards the southern extent of their range, in Brazil, they are found almost exclusively along the coast, rarely venturing inland at all.<p>Juveniles in San Blas, in the Mexican state of Nayarit have an atypical color-scheme. In these birds, the top of the head is chestnut colored and the wings tips are much darker. Initially, it was suggested that they may be hybrids, however further study concluded they were most likely a natural variation. No other geographic varieties have been observed.

迁徙

Complete migrants

行为

Migration pattern: Complete migrants.

保护状况

Population trend: declining.

种群趋势

declining