Little blue heron

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Little blue heron
Egretta caerulea -Cananeia, Sao Paulo, Brasil-8.jpg
Adult little blue heron in Cananeia, São Paulo, Brazil
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Pelecaniformes
Family: Ardeidae
Genus: Egretta
Species:
E. caerulea
Binomial name
Egretta caerulea
Egretta caerulea map.svg
Distribution of Egretta caerulea:
  breeding
  non-breeding
  year-round
  migration
Synonyms

Ardea caeruleaLinnaeus, 1758

Little blue heron Little Blue Heron during the day.jpg
Little blue heron

The little blue heron [note 1] (Egretta caerulea) is a small heron of the genus Egretta . It is a small, darkly colored heron with a two-toned bill. Juveniles are entirely white, bearing resemblance to the snowy egret. During the breeding season, adults develop different coloration on the head, legs, and feet.

Contents

They have a range that encompasses much of the Americas, from the United States to northern South America. Some populations are migratory. Climate change will probably cause their distribution to spread north. They can be found in both saltwater and freshwater ecosystems. Their preference for either one depends on where they live.

Nesting behaviors are documented by numerous sources. The adults build nests in trees, in colonies with other bird species. The number of eggs laid varies from place to place. The young mature quickly, requiring little attention from adults after about nineteen days of age. Both young and adults are sometimes preyed on by other species. Adults hunt fish, crabs, and other small animals. As with clutch sizes, diet can vary regionally.

The population of E. caerulea is declining. Many possible reasons for this have been proposed. Exposure to heavy metals has been found to have detrimental effects on young birds.

Taxonomy

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. [3] It was first described as Ardea caerulea by Carl Linnaeus in his 10th edition of Systema Naturae. [4] It is now a member of the genus Egretta . [3] It may be closely related to the snowy egret, another member of its genus, which it greatly resembles when young. [5] Variations of the name include Ardea coerulea, Florida caerulea, and Hydranassa caerulea. [2]

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. [6] 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. [2]

Description

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). [7] [8]

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. [9] 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). [10]

Distribution and habitat

juvenile, Macal River, Cayo, Belize Little blue heron (Egretta caerulea) juvenile Cayo.jpg
juvenile, Macal River, Cayo, Belize

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. [1] 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. [7] They can occasionally roam as far north as Canada. [3]

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. [3] 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). [11]

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. [5]

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. [1] [8] They are usually found at low elevations, but can be seen at heights of 3,700 metres (12,100 ft) in the Andes. [9]

In North America, they tend to favor freshwater habitats, while in the Caribbean, they are more often found in saltwater. [5] Towards the southern extent of their range, in Brazil, they are found almost exclusively along the coast, rarely venturing inland at all. [10]

Regional variations

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. [12] No other geographic varieties have been observed. [9]

Behavior and ecology

A close up of a little blue heron's head at Lake Apopka, Florida Little Blue Heron Portrait.jpg
A close up of a little blue heron's head at Lake Apopka, Florida
Sounds of Egretta caerulea

Little blue herons prefer to stand still and wait when hunting, rather than chase after prey. They walk slowly and search for fish and other prey items, flying to different spots if needed. They tend to move slower than other related species, which can help distinguish them. They are not usually found in large numbers at any body of water. Occasionally, however, they will gather with other herons, especially if they have found a school of fish trapped in shallow water. [8] They sometimes also feeds in grassy fields. [5]

Reproduction and life cycle

During courtship, both males and females practice bill-nibling. Males also use a neck-stretch to attract mates. [13]

Nesting

Little blue herons typically nest in trees alongside other roosting birds. [8] They are colonial nesters (nesting in groups). Examples of species they may nest alongside include the scarlet ibis, yellow-crowned night heron, great egret, black-crowned night heron, and snowy egret. [10]

During nest construction, males bring twigs to females, who use them to build the nest. Both males and females help incubate their clutch. [13] They begin incubation after two eggs have been laid, which will cause any later eggs to hatch out of sync. The chicks that hatch later tend to not receive as much food as early-hatching ones, which limits their growth. [14] Clutch sizes vary significantly throughout their range. In Trinidad, there are usually 2–5 eggs, while in Costa Rica, only 2–4 are laid on average. In North America, the mean is 2.67–4.4. The very lowest values are seen in southeastern Brazil and the US states Florida and Georgia, where no more than three are generally laid. [10]

Young herons are able to start climbing around the branches by their nests at 15 days old. [10] Due to the young age at which they develop motor skills in their legs, the young do not rely on their parents for anything besides feeding after 19 days, at which point the adults begin foraging away from the nest. [14] By 20–25 days, they can climb to the very top of the tree their nest is built on, or even into other trees. They can fly short distances at around 30 days of age (some take 35–38), but will still be dependent on adults for about two weeks after that. [10] It is in their second year of life that juveniles begin to lose their white feathers. [9]

Predation

There is circumstantial evidence that young black-crowned night herons and crab-eating raccoons prey on nestling little blue herons. Adults have been observed driving a yellow-headed caracara away from their nests. In the presence of a Harris' hawk, however, the little blue herons fled. [10]

Parasites

Twenty-four different species of parasitic worms were found on 33 of 35 little blue herons examined in South Florida. These included trematodes, nematodes, acanthocephalans, and one cestode. The most common trematode was Posthodiplostomum macrocotyle , and the most common nematodes were Contracaecum multipapillatum and Contracaecum microcephalum . The acanthocephalan and cestode species could not be identified (in the latter, neither could the genus). [15]

Prey

On the eastern coast of North America, little blue herons primarily feed on fish, however their diet varies significantly throughout their range. [9] In a study of individuals in mangrove forests in southeastern Brazil, 80% of their diet during the breeding season was found to consist of crabs. Compared to the scarlet ibis, the herons preferred arboreal or semi-arboreal species, such as Aratus pisonii and Metasesarma rubripes , while the former preferred to take burrowing species. This demonstrates their different feeding strategies—scarlet ibises being foragers who hunt using their sense of touch and little blue herons being visual hunters. [16] In another mangrove forest in southwestern Puerto Rico, the entire diet was found to consist of fiddler crabs. [17]

Conservation

The little blue heron is listed as a least-concern species by the International Union for the Conservation of Nature, although its numbers are decreasing. [1] Historically, they were not hunted for their feathers as much as other heron species due to their lack of visually attractive plumes. [8]

The dangers faced by Egretta caerulea are not well researched. They could include development along coastlines, habitat disturbance, predators, pesticide exposure, and parasites. [7] The metals cadmium and lead have been found to lead to slower growth rates and higher death rates, respectively, of young birds. [18] In Sepetiba Bay, Rio de Janeiro, Brazil, little blue herons were found to have relatively high levels of metal contamination in the liver and kidneys. [19]

In areas with cattle egrets, little blue herons have been found to nest for shorter amounts of time, and produce fewer young that survive to adulthood. Cattle egrets only begin pairing when most little blue herons already have eggs or live young in their nests. The former species has been observed stealing twigs from nests of the latter. This behavior sometimes leads to the young falling out of the nest or the cattle egrets removing them. [20]

Related Research Articles

<span class="mw-page-title-main">Egret</span> Type of bird of the heron family

Egrets are herons, generally long-legged wading birds, that have white or buff plumage, developing fine plumes during the breeding season. Egrets are not a biologically distinct group from herons and have the same build.

<span class="mw-page-title-main">Great blue heron</span> Species of bird

The great blue heron is a large wading bird in the heron family Ardeidae, common near the shores of open water and in wetlands over most of North and Central America, as well as far northwestern South America, the Caribbean and the Galápagos Islands. It is occasionally found in the Azores and is a rare vagrant to Europe. An all-white population found in south Florida and the Florida Keys is known as the great white heron. Debate exists about whether this represents a white color morph of the great blue heron, a subspecies of it, or an entirely separate species.

<span class="mw-page-title-main">American white ibis</span> Bird in the ibis family

The American white ibis is a species of bird in the ibis family, Threskiornithidae. It is found from Virginia via the Gulf Coast of the United States south through most of the coastal New World tropics. This particular ibis is a medium-sized bird with an overall white plumage, bright red-orange down-curved bill and long legs, and black wing tips that are usually only visible in flight. Males are larger and have longer bills than females. The breeding range runs along the Gulf and Atlantic Coast, and the coasts of Mexico and Central America. Outside the breeding period, the range extends further inland in North America and also includes the Caribbean. It is also found along the northwestern South American coastline in Colombia and Venezuela. Populations in central Venezuela overlap and interbreed with the scarlet ibis. The two have been classified by some authorities as a single species.

<span class="mw-page-title-main">Heron</span> Family of birds

Herons are long-legged, long-necked, freshwater and coastal birds in the family Ardeidae, with 72 recognised species, some of which are referred to as egrets or bitterns rather than herons. Members of the genera Botaurus and Ixobrychus are referred to as bitterns, and, together with the zigzag heron, or zigzag bittern, in the monotypic genus Zebrilus, form a monophyletic group within the Ardeidae. Egrets do not form a biologically distinct group from herons, and tend to be named differently because they are mainly white or have decorative plumes in breeding plumage. Herons, by evolutionary adaptation, have long beaks.

<span class="mw-page-title-main">Great egret</span> Species of bird

The great egret (Ardea alba), also known as the common egret, large egret, or great white egret or great white heron, is a large, widely distributed egret. The four subspecies are found in Asia, Africa, the Americas, and southern Europe. Recently it is also spreading to more northern areas of Europe. Distributed across most of the tropical and warmer temperate regions of the world, it builds tree nests in colonies close to water.

<span class="mw-page-title-main">Yellow-crowned night heron</span> Species of bird

The yellow-crowned night heron, is one of two species of night heron in genus Nyctanassa. Unlike the black-crowned night heron, which has a worldwide distribution, the yellow-crowned is restricted to the Americas. It is known as the bihoreau violacé in French and the pedrete corona clara or yaboa común in some Spanish-speaking countries.

<span class="mw-page-title-main">Snowy egret</span> Species of bird

The snowy egret is a small white heron. The genus name comes from Provençal French for the little egret, aigrette, which is a diminutive of aigron, 'heron'. The species name thula is the Araucano term for the black-necked swan, applied to this species in error by Chilean naturalist Juan Ignacio Molina in 1782.

<span class="mw-page-title-main">Little egret</span> Species of water bird

The little egret is a species of small heron in the family Ardeidae. It is a white bird with a slender black beak, long black legs and, in the western race, yellow feet. As an aquatic bird, it feeds in shallow water and on land, consuming a variety of small creatures. It breeds colonially, often with other species of water birds, making a platform nest of sticks in a tree, bush or reed bed. A clutch of three to five bluish-green eggs is laid and incubated by both parents for about three weeks. The young fledge at about six weeks of age.

<span class="mw-page-title-main">Cattle egret</span> Cosmopolitan genus of heron

The cattle egret (Bubulcus) is a cosmopolitan genus of heron found in the tropics, subtropics, and warm-temperate zones. According to the IOC bird list, it contains two species, the western cattle egret and the eastern cattle egret, although some authorities regard them as a single species. Despite the similarities in plumage to the egrets of the genus Egretta, it is more closely related to the herons of Ardea. Originally native to parts of Asia, Africa, and Europe, it has undergone a rapid expansion in its distribution and successfully colonised much of the rest of the world in the last century.

<span class="mw-page-title-main">Western reef heron</span> Species of bird

The western reef heron, also called the western reef egret, is a medium-sized heron found in southern Europe, Africa and parts of Asia. It has a mainly coastal distribution and occurs in several plumage forms: a slaty-grey plumage in which it can only be confused with the rather uncommon dark morph of the Little egret ; a white form which can look very similar to the little egret although the bill tends to be paler and larger and the black form with white throat E. g. gularis of West Africa. There are also differences in size, structure and foraging behaviour. There have been suggestions that the species hybridizes with the Little Egret, and based on this, some authors treat schistacea and gularis as subspecies of Egretta garzetta. Works that consider the Western Reef Heron as a valid species include the nominate gularis and schistacea as subspecies.

<span class="mw-page-title-main">White-faced heron</span> Species of bird

The white-faced heron also known as the white-fronted heron, and incorrectly as the grey heron, or blue crane, is a common bird throughout most of Australasia, including New Guinea, the islands of Torres Strait, Indonesia, New Zealand, and all but the driest areas of Australia.

<span class="mw-page-title-main">Tricolored heron</span> Species of bird

The tricolored heron, formerly known as the Louisiana heron, is a small species of heron native to coastal parts of the Americas. The species is more solitary than other species of heron in the Americas and eats a diet consisting mostly of small fish.

<span class="mw-page-title-main">Medium egret</span> Species of bird

The intermediate egret, median egret, smaller egret or medium egret is a medium-sized heron. Some taxonomists put the species in the genus Egretta or Mesophoyx. It is a resident breeder in southern and eastern Asia.

<span class="mw-page-title-main">Milky stork</span> Species of bird

The milky stork is a stork species found predominantly in coastal mangroves around parts of Southeast Asia. It is native to parts of Cambodia, Vietnam, Malaysia and Indonesia. They were once part of the genus Ibis, but is currently included in the genus Mycteria, due to similarities with other storks in that genus.

<i>Egretta</i> Genus of birds

Egretta is a genus of medium-sized herons, mostly breeding in warmer climates.

<span class="mw-page-title-main">Malagasy pond heron</span> Species of bird

The Malagasy pond heron, also known as the Madagascar pond heron or Madagascar squacco heron, is a species of heron of the family Ardeidae. They breed in Madagascar, Réunion and the Seychelles, and spend the non-breeding season in eastern mainland Africa. The population is estimated to number only 1,300–4,000 adults and the species is considered endangered.

<span class="mw-page-title-main">Malagasy sacred ibis</span> Species of bird

The Malagasy sacred ibis is a relatively large, heavily built ibis endemic to the west coast of Madagascar, and Aldabra on the Seychelles.

Sipacate-Naranjo National Park is located along the Pacific coast of Escuintla in Guatemala. The park includes mangrove forests, lagoons and sandy beaches and covers an area of 20 km long and 1 km wide, stretching between the coastal towns of Sipacate and El Naranjo.

<span class="mw-page-title-main">Eastern cattle egret</span> Species of bird

The eastern cattle egret is a species of heron found in the tropics, subtropics and warm temperate zones. Most taxonomic authorities lump this species and the western cattle egret together as subspecies of the cattle egret, but some separate them. Despite the similarities in plumage to the egrets of the genus Egretta, it is more closely related to the herons of Ardea. It is native to southern and eastern Asia, and Australasia.

<span class="mw-page-title-main">Western cattle egret</span> Species of bird

The western cattle egret is a species of heron found in the tropics, subtropics and warm temperate zones. Most taxonomic authorities lump this species and the eastern cattle egret together, but some separate them. Despite the similarities in plumage to the egrets of the genus Egretta, it is more closely related to the herons of Ardea. Originally native to parts of Asia, Africa and Europe, it has undergone a rapid expansion in its distribution and successfully colonised much of the rest of the world in the last century.

References

  1. 1 2 3 4 BirdLife International (2017). "Egretta caerulea". IUCN Red List of Threatened Species . 2017: e.T22696944A118857172. doi: 10.2305/IUCN.UK.2017-3.RLTS.T22696944A118857172.en . Retrieved 13 November 2021.
  2. 1 2 3 "Little Blue Heron Egretta caerulea (Linnaeus, C 1758)". Avibase . Retrieved 8 October 2022.
  3. 1 2 3 4 Cottrell, G. William; Greenway, James C.; Mayr, Ernst; Paynter, Raymond A.; Peters, James Lee; Traylor, Melvin A.; University, Harvard (1979). Check-list of birds of the world. Vol. 1. Cambridge: Harvard University Press. pp. 211–212. Archived from the original on 2022-09-30. Retrieved 2022-09-30.
  4. ↑ Linné, Carl von; Salvius, Lars (1758). Caroli Linnaei...Systema naturae per regna tria naturae :secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Vol. 1. Holmiae: Impensis Direct. Laurentii Salvii. p. 143. Archived from the original on 2017-03-25. Retrieved 2022-09-30.
  5. 1 2 3 4 "Little Blue Heron". Audubon . 13 November 2014. Retrieved 5 October 2022.
  6. ↑ Bartos, Alisa J.; Igl, Lawrence; Sovada, Marsha A. (2010). "Observations of Little Blue Herons nesting in North Dakota, and an instance of probable natural hybridization between a Little Blue Heron and a Cattle Egret". The Prairie Naturalist. Retrieved 5 October 2022.
  7. 1 2 3 "Little blue heron". Florida Fish and Wildlife Conservation Commission . Archived from the original on 29 September 2022. Retrieved 28 September 2022.
  8. 1 2 3 4 5 "Little Blue Heron". The Cornell Lab. Archived from the original on 28 September 2022. Retrieved 28 September 2022.
  9. 1 2 3 4 5 "Little Blue Heron". Heron Conservation. Retrieved 8 October 2022.
  10. 1 2 3 4 5 6 7 Olmos, Fábio; Silva e Silva, Robson (2002). "Breeding Biology of the Little Blue Heron (Egretta Caerulea) in Southeastern Brazil" (PDF). Ornitologia Neotropical. The Neotropical Ornithological Society. Archived (PDF) from the original on 29 September 2022. Retrieved 29 September 2022.
  11. ↑ Melvin, Stefani L.; Gawlik, Dale E.; Scharff, T. (1999). "Long-Term Movement Patterns for Seven Species of Wading Birds". Waterbirds: The International Journal of Waterbird Biology. 22 (3): 411–416. doi:10.2307/1522117. JSTOR   1522117 . Retrieved 4 October 2022.
  12. ↑ Dickerman, Robert W.; Parkes, Kenneth C. (1963). "Notes on the Plumages and Generic Status of the Little Blue Heron". The Auk. 85 (3): 437–440. doi: 10.2307/4083292 . JSTOR   4083292 . Retrieved 5 October 2022.
  13. 1 2 Rodgers, James A. (April 1980). "Little Blue Heron Breeding Behavior". The Auk . 97 (2). Retrieved 8 October 2022.
  14. 1 2 Werschkul, David F. (January 1979). "Nestling Mortality and the Adaptive Significance of Early Locomotion in the Little Blue Heron". The Auk . 96 (1). Retrieved 8 October 2022.
  15. ↑ Sepúlveda, María Soledad; Spalding, Marilyn G.; Kinsella, John M.; Forrester, Donald J. (January 1996). "Parasitic Helminths of the Little Blue Heron, Egretta caerulea, in Southern Florida". Comparative Parasitology .
  16. ↑ Olmos, Fábio; Silva E Silva, Robson; Prado, Ariadne (April 2001). "Breeding Season Diet of Scarlet Ibises and Little Blue Herons in a Brazilian Mangrove Swamp". Waterbirds . 24 (1): 50–57. doi:10.2307/1522243. JSTOR   1522243 . Retrieved 8 October 2022.
  17. ↑ Collazo, Jaime A.; Miranda, Leopoldo (1997). "Food Habits of 4 Species of Wading Birds (Ardeidae) in a Tropical Mangrove Swamp". Colonial Waterbirds . 20 (3): 413–418. doi:10.2307/1521591. JSTOR   1521591 . Retrieved 8 October 2022.
  18. ↑ Spahn, S. A.; Sherry, T. W. (1999-10-01). "Cadmium and Lead Exposure Associated with Reduced Growth Rates, Poorer Fledging Success of Little Blue Heron Chicks (Egretta caerulea) in South Louisiana Wetlands". Archives of Environmental Contamination and Toxicology. 37 (3): 377–384. doi:10.1007/s002449900528. ISSN   1432-0703. PMID   10473795. S2CID   30144426. Archived from the original on 2022-10-03. Retrieved 2022-09-30.
  19. ↑ Ferreira, Aldo Pacheco (December 2010). "Estimation of heavy metals in little blue heron (Egretta caerulea) collected from sepetiba bay, rio de janeiro, brazil". Brazilian Journal of Oceanography . 58 (4): 269–274. doi: 10.1590/S1679-87592010000400002 . Retrieved 15 October 2022.
  20. ↑ Werschkul, David F. (1978). "Observations on the Impact of Cattle Egrets on the Reproductive Ecology of the Little Blue Heron". Proceedings of the Colonial Waterbird Group. 1: 131–138. doi:10.2307/1520910. JSTOR   1520910 . Retrieved 15 October 2022.

Notes

  1. ↑ Also known as the garceta azul in Spanish. [2]
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