cerulean warbler
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The cerulean warbler (''Setophaga cerulea'') is a small
songbird A songbird is a bird belonging to the suborder Passeri of the perching birds (Passeriformes). Another name that is sometimes seen as the scientific or vernacular name is Oscines, from Latin ''oscen'', "songbird". The Passeriformes contains 5000 ...
in the family Parulidae. It is a long-distance migrant, breeding in eastern North American hardwood forests. In the non-breeding season, it winters on the eastern slope of the
Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...
in South America, preferring subtropical forests. It displays strong
sexual dichromatism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...
: Adult males have
cerulean blue Cerulean (), also spelled caerulean, is a shade of blue ranging between azure and a darker sky blue. The first recorded use of ''cerulean'' as a colour name in English was in 1590. The word is derived from the Latin word '' caeruleus'', "dar ...
and white , with a black necklace across the breast and black streaks on the back and flanks. Females and immature birds have bluish-green upperparts, a pale stripe over the eye, no streaking, and are yellow below. All have two white wing bars and a thin, pointed . The cerulean warbler is
insectivorous A robber fly eating a hoverfly An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects. The first vertebrate insectivores were ...
and predominantly feeds on
insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pa ...
larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...
e, though it also takes winged insects. It forages for prey and nests high in forest canopies. Individuals are strongly
territorial A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or an ...
; males will defend areas of forests. Males arrive on breeding grounds about one to two weeks earlier than females. Breeding and incubation take place from late May to early June. The species is rated as
near threatened A near-threatened species is a species which has been categorized as "Near Threatened" (NT) by the International Union for Conservation of Nature as that may be vulnerable to endangerment in the near future, but it does not currently qualify fo ...
on the
International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...
(IUCN)'s Red List of endangered species, indicating it is under risk of becoming vulnerable in the near future. The population of the cerulean warbler has been under rapid decline, though in recent years this decline has slowed.
Deforestation Deforestation or forest clearance is the removal of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. The most concentrated ...
in its non-breeding range continues to reduce its available habitat.


Taxonomy and systematics

The cerulean warbler was described in 1810 as ''Sylvia cerulea'' by ornithologist Alexander Wilson. In 1811, Wilson described the female as a separate species, ''Sylvia rara''. It was later realized that the two taxa were
conspecific Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species. Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organis ...
, and in 1838 the biologist
Charles Lucien Bonaparte Charles Lucien Jules Laurent Bonaparte, 2nd Prince of Canino and Musignano (24 May 1803 – 29 July 1857), was a French naturalist and ornithologist. Lucien and his wife had twelve children, including Cardinal Lucien Bonaparte. Life and career ...
merged them together. In 1842, it was placed in the new genus ''Dendroica'' introduced by the ornithologist
George Robert Gray George Robert Gray FRS (8 July 1808 – 6 May 1872) was an English zoologist and author, and head of the ornithological section of the British Museum, now the Natural History Museum, in London for forty-one years. He was the younger brother ...
. In 2011, ''Dendroica'' was merged into the genus ''
Setophaga ''Setophaga'' is a genus of birds of the New World warbler family Parulidae. It contains at least 33 species. The males in breeding plumage are often highly colorful. The ''Setophaga'' warblers are an example of adaptive radiation with the vario ...
'' after molecular studies showed that the two genera were not well delineated''.'' The change was implemented as part of the ''Fifty-second Supplement to the AOU Checklist of North American Birds''. The genus name ''Setophaga'' is derived from the Greek ''ses'', "moth", and ''phagos'', "eating". The specific name, ''cerulea'', is derived from ''caeruleus,'' Latin for "blue", "azure". Between 1897 and 1903, it was believed that the name ''Sylvia cærulea'' (an unjustified emendation of ''cerulea'') had been preoccupied by the
blue-gray gnatcatcher The blue-gray gnatcatcher or blue-grey gnatcatcher (''Polioptila caerulea'') is a very small songbird native to North America. Description It is in length, 6.3 in (16 cm) in wingspan, and weighing only . Adult males are blue-gray on the upperpa ...
, ''Polioptila cærulea'', as ornithologist John Latham had in 1793 moved the latter species to ''Sylvia''. Therefore, the name ''Sylvia rara'', an obsolete name for the female cerulean warbler, was accepted as ''Dendroica rara'' in the ''Eighth Supplement to the AOU Checklist of North American Birds''. However, in 1903, it was found that the change was invalid, and the accepted name reverted to ''Dendroica cerulea''. The cerulean warbler's close relatives within the genus ''Setophaga'' include the Blackburnian warbler (''S. fusca''), blackpoll warbler (''S. striata''), chestnust-sided warbler,
Wilson's warbler Wilson's warbler (''Cardellina pusilla'') is a small New World warbler. It is greenish above and yellow below, with rounded wings and a long, slim tail. The male has a black crown patch; depending on the subspecies, that mark is reduced or absent ...
(''S. pensylvanica'') and bay-breasted warbler (''S. castanea)''. Hybridisations with the
northern parula The northern parula (''Setophaga americana'') is a small New World warbler. It breeds in eastern North America from southern Canada to Florida. Description The northern parula is one of the smaller North American migratory warblers, often being ...
(''S. americana'') have been observed, indicating a close relationship. The following cladograms show the position of the cerulean warbler among its closest relatives according to Lovette et al. 2010 (left), and Baiz et al. 2021 (right): Lovette et al. (2010) Baiz et al. (2021)


Description

The cerulean warbler is one of the smallest ''Setophaga'' wood-warblers, about long, weighing , and having a
wingspan The wingspan (or just span) of a bird or an airplane is the distance from one wingtip to the other wingtip. For example, the Boeing 777–200 has a wingspan of , and a wandering albatross (''Diomedea exulans'') caught in 1965 had a wingspan o ...
of . Males are slightly larger than females, and older males tend to also be larger. Wing chord measures , while the tail is long. The culmen, or upper edge of the
beak The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for fo ...
, measures long, wide and height. The cerulean warbler is strongly sexually dichromatic. Adult males are a deep, cerulean blue over the entire back, and are white below. There are prominent dark streaks across the flanks. A "necklace" or breast band, a line of color across the neck, varies from blue to near black. Older individuals have stronger colors across the entire body, including brighter whites, darker streaking, and wider breast bands. Adult females are yellow underneath, while the back and have a blue-green tint. Females also possess a distinct pale
supercilium The supercilium is a plumage feature found on the heads of some bird species. It is a stripe which runs from the base of the bird's beak above its eye, finishing somewhere towards the rear of the bird's head.Dunn and Alderfer (2006), p. 10 Also k ...
, or eye stripe, just above the eye. Immature individuals are generally similar to adult females, though the back may be more yellowish. All
fledged Fledging is the stage in a flying animal's life between hatching or birth and becoming capable of flight. This term is most frequently applied to birds, but is also used for bats. For altricial birds, those that spend more time in vulnerable ...
individuals, regardless of their age or sex, have two prominent white wing-bars and white spots on the tail. The beak and
legs A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element c ...
of the cerulean warbler vary in color depending on an individual's age and sex. Adult males have a black beak, with the lower half a slightly lighter dark grey. Adult females have dark grey beaks that may become dark brown on the lower half. Recently fledged birds have a brownish beak. Adults have black legs and brown irises, while juveniles have dark brown legs and dark brown irises. Hatchlings have pink bare parts, including the beak and legs, and black eyes. The
song A song is a musical composition intended to be performed by the human voice. This is often done at distinct and fixed pitches (melodies) using patterns of sound and silence. Songs contain various forms, such as those including the repetiti ...
is a buzzed accelerating ''zray zray zray zray zeeee''. The primary call is a buzzy, metallic ''zzee''. Males use their songs to attract potential mates and to mark out their territory. Cerulean warblers are also capable of imitating the songs of other birds alongside their typical song. Females rarely sing, but often call when nesting. An alarm call is used to signal the arrival of a predator or another bird threatening the nest.


Distribution and habitat

The cerulean warbler's preferred summer habitat consists of large, unfragmented mature
deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, ...
hardwood forests. Nesting takes place in the top canopy, often above heights of , and territories are typically about .
Foraging Foraging is searching for wild food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce. Foraging theory is a branch of behavioral ecology that studies the foraging behavi ...
is done throughout the mid to high canopy. Generally, to support a population of cerulean warblers, a forested area of greater than is required.
Riparian A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the terrestrial biomes of the Earth. Plant habitats and communities along the river margins and banks a ...
areas are commonly selected. The breeding range extends from southern Tennessee to southern Ontario, and is bounded in the east by the Atlantic Ocean and on the west by the
Great Plains The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland in North America. It is located west of the Mississippi River and east of the Rocky Mountains, much of it covered in prairie, steppe, a ...
. The majority of the population breeds in forests of the
Appalachian mountains The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. The ...
, with smaller numbers in forests throughout the United States and Canada. Historically, the cerulean warbler was common to abundant as far south as Alabama and Mississippi, but loss of habitat in these southern regions has caused the centre of its breeding range to shift northwards. The cerulean warbler migrates distances of over between its breeding and non-breeding ranges. In the spring, it takes an overland route through Central America, passing over water only to cross the
Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United ...
at the
Yucatán Peninsula The Yucatán Peninsula (, also , ; es, Península de Yucatán ) is a large peninsula in southeastern Mexico and adjacent portions of Belize and Guatemala. The peninsula extends towards the northeast, separating the Gulf of Mexico to the north ...
. In the autumn, it may overfly the Caribbean Sea, crossing from Florida to Cuba onto continental
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...
. Migration takes from 40–70 days; much of this time is made up of stopovers, where birds will remain at one individual location for 2–18 days. The non-breedingrange covers a broad area of northern South America, and extends southwards along the
Andes mountains The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...
. Individuals have been found as far south as Bolivia, while in the north it is often found throughout Colombia and Venezuela. The cerulean warbler prefers tall forest; its occurrence is therefore strongly correlated with the presence of old-growth subtropical forests or shade coffee
plantation A plantation is an agricultural estate, generally centered on a plantation house, meant for farming that specializes in cash crops, usually mainly planted with a single crop, with perhaps ancillary areas for vegetables for eating and so on. Th ...
s. It is found at altitudes of in its non-breeding range. The cerulean warbler has been recorded as a vagrant to Iceland. It has also been recorded in Brazil, far outside of its range.


Behaviour


Feeding

The cerulean warbler forages throughout the forest canopy, predominantly at middle to top layers. It hops from branch to branch, gleaning small soft-bodied insects from leaves and twigs. In the non-breeding season, it may also glean insects from flowers. Its preferred prey consists of butterfly and moth (
lepidoptera Lepidoptera ( ) is an order of insects that includes butterflies and moths (both are called lepidopterans). About 180,000 species of the Lepidoptera are described, in 126 families and 46 superfamilies, 10 percent of the total described speci ...
n larvae), though it supplements its diet with winged insects. In its non-breeding range, it preferentially forages on trees of the genus '' Inga.'' Foraging is vertically segregated; males tend to forage at somewhat higher elevations in the canopy than females. The difference in height average is about . They stay with mixed-species flocks as they forage, sharing spaces with species such as the American redstart (''Setophaga ruticilla''), Blackburnian warbler, and Tennessee warbler (''Leiothlypis peregrina''). The other species forage at different heights and substrates, preventing competition. At the high elevations and relatively sparser vegetation that the cerulean warbler prefers, the gleaning technique it uses is more effective than aerial maneouvreing. Foraging locations tend to be lower than nest placements.


Breeding

The cerulean warbler is
monogamous Monogamy ( ) is a form of dyadic relationship in which an individual has only one partner during their lifetime. Alternately, only one partner at any one time ( serial monogamy) — as compared to the various forms of non-monogamy (e.g., pol ...
. Its short breeding season allows it to produce one brood a year. Individuals are very aggressive towards others of the same sex during the breeding season. Typical conflict comprises the use of song to mark a territory, as well as physical conflict such as attacks in which individuals may fall from heights of . Female cerulean warblers have been observed to attack other females and destroy their eggs.
Nest A nest is a structure built for certain animals to hold eggs or young. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of organic materi ...
construction takes about 7 days. The female lays from 3 to 5 eggs over the course of about 7 days, incubation lasts for around 12 days, and nestlings remain
altricial In biology, altricial species are those in which the young are underdeveloped at the time of birth, but with the aid of their parents mature after birth. Precocial species are those in which the young are relatively mature and mobile from the mome ...
for an average of 11 days. Only the female broods the nest, but the male will frequently provide food for the female and for the young. The female occasionally responds with a call. During nesting, the female vocalizes a ''chip'' call whenever it leaves the nest. In response, the male returns to the nest, guarding it from a nearby perch. Extra-pair copulation, in which mating occurs outside of a monogamous pair, is known to occur. Based on blood analyses, several young may be sired by a different male than that which occupies the territory on which the young are found, making it likely that males travelling outside of their own territories seek extra-pair copulations. Males engage in mate guarding, in which they will remain close to the mate during periods of foraging, nest building, or nest site selection. The male will also frequently sing a "whisper song"; the female occasionally responds with a call. During nest incubation, and when young are in the nestling stage, the female may also sing. The song, a more complex variation of the typical nest call, is a metallic ''zee zeet zee zeet zeet''. Both males and females are involved in nest construction and together choose a nest site. Sites are usually located on horizontal branches high in the forest canopy, and are usually shaded by vegetation. The cerulean warbler prefers to nest over an empty space where there are no branches for or more. The nest itself is made from tree bark, grasses, and lichens, woven together using caterpillar silk and spider thread. If a nesting attempt is unsuccessful, individuals will often reuse materials from an old nest, especially binding elements. Cerulean warblers have been observed to construct "double-decker" nests, in which a new nest is overlaid atop an existing one. Nearly all known nests have been in deciduous trees, but nesting has been recorded in pine trees in southern Indiana. After the eggs have hatched, nestlings are fed by their parents, mainly consuming lepidopteran larvae. The fledglings become independent about 12 days after leaving the nest. Survival rates range from 34-62% for the fledgling stage of development. Newly fledged birds are often killed by
chipmunks Chipmunks are small, striped rodents of the family Sciuridae. Chipmunks are found in North America, with the exception of the Siberian chipmunk which is found primarily in Asia. Taxonomy and systematics Chipmunks may be classified either as ...
through predation. Young individuals have somewhat different feeding patterns than adults, preferring riparian areas with relatively little foliage.Douglas W Raybuck, Jeffery L Larkin, Scott H Stoleson, Than J Boves, Radio-tracking reveals insight into survival and dynamic habitat selection of fledgling Cerulean Warblers, ''The Condor'', Volume 122, Issue 1, 3 February 2020, duz063, https://doi.org/10.1093/condor/duz063


Predators and parasites

The cerulean warbler's preferred nesting sites, located high in the forest canopy, reduce the prevalence of nest predation. However, its eggs and young still fall victim to predators such as raccoons, squirrels, chipmunks,
snakes Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more j ...
, and birds, in particular blue jays (''Cyanocitta cristata''). The cerulean warbler is known to be parasitized by blood parasites such as '' Haemoproteus paruli.'' Nest parasitism by
brown-headed cowbird The brown-headed cowbird (''Molothrus ater'') is a small, obligate brood parasitic icterid native to temperate and subtropical North America. It is a permanent resident in the southern parts of its range; northern birds migrate to the southern ...
s (''Molothrus ater'') occurs, but is less common in the dense interior canopy the cerulean warbler prefers.


Status and conservation

The cerulean warbler is currently rated a
near threatened A near-threatened species is a species which has been categorized as "Near Threatened" (NT) by the International Union for Conservation of Nature as that may be vulnerable to endangerment in the near future, but it does not currently qualify fo ...
species by the
International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...
. It is the fastest declining
Neotropical The Neotropical realm is one of the eight biogeographic realms constituting Earth's land surface. Physically, it includes the tropical terrestrial ecoregions of the Americas and the entire South American temperate zone. Definition In bioge ...
migrant songbird. Among the many threats it faces, its wintering habitat in the northern Andes is dwindling rapidly. Cerulean warblers depend on shade coffee plantations for the mature forest habitat they require. This traditional farming technique faces pressure from fluctuating world coffee prices, and many tracts of shade coffee are being converted to higher-yield sun coffee or other crops. In fragmented forest areas, the cerulean warbler is vulnerable to nest parasitism by the brown-headed cowbird. Historically, the preferred habitat of tall forest interiors protected it from brood parasitism, but deforestation has caused the cerulean warbler to often choose nest locations accessible to cowbirds. This bird's numbers are declining faster than any other warbler species in the USA; its population in 2006 was less than one-fifth of what it was 40 years before. The American Bird Conservancy (ABC) is working with its Colombian partner, Fundación ProAves, to protect wintering habitat for cerulean warblers and other migratory songbirds. In 2008, the partnership created the
Cerulean Warbler Bird Reserve Cerulean Warbler Bird Reserve, known in Spanish as Reserva Natural de las Aves Reinita Cielo Azul, is a nature reserve near Bucaramanga in central Colombia. The reserve is set among oak forest on the eastern slopes of the Magdalena River. It ...
, the first protected area created for a neotropical migrant. In an effort to advance protection of the cerulean warbler, ABC and its South American partners (Fundacion ProAves, ECOAN and Fundacion Jocotoco), in 2009 produced a Cerulean Warbler Wintering Ground Conservation Plan.


In art and culture

Artist and ornithologist
John James Audubon John James Audubon (born Jean-Jacques Rabin; April 26, 1785 – January 27, 1851) was an American self-trained artist, naturalist, and ornithologist. His combined interests in art and ornithology turned into a plan to make a complete pictori ...
illustrates the cerulean warbler in '' Birds of America'' (London, 1827–38) as Plate 48, where two birds are shown perched in a dahoon holly bush. The painting was originally produced in 1822, and engraved and colored by Robert Havell's London workshops. The original watercolor by Audubon was purchased by the
New-York Historical Society The New-York Historical Society is an American history museum and library in New York City, along Central Park West between 76th and 77th Streets, on the Upper West Side of Manhattan. The society was founded in 1804 as New York's first museum ...
, where it remains as of 2022. The novelist
Jonathan Franzen Jonathan Earl Franzen (born August 17, 1959) is an American novelist and essayist. His 2001 novel ''The Corrections'', a sprawling, satirical family drama, drew widespread critical acclaim, earned Franzen a National Book Award, was a Pulitzer Pri ...
uses the cerulean warbler as a plot device in his 2010 novel ''
Freedom Freedom is understood as either having the ability to act or change without constraint or to possess the power and resources to fulfill one's purposes unhindered. Freedom is often associated with liberty and autonomy in the sense of "giving one ...
''. In San Vicente, Colombia, the cerulean warbler is commemorated in an annual migratory bird festival. The Man in the Yellow Hat publishes a book about the cerulean warbler in the episode "The Big Picture" of ''
Curious George Curious George is a fictional monkey who is the title character of a series of popular children's picture books written by Margret and H. A. Rey. Various media, including films and TV shows, have been based upon the original book series. Geo ...
''.


References


External links

* * {{Taxonbar, from=Q25066647 cerulean warbler Birds of Appalachia (United States) Native birds of the Eastern United States Native birds of the Northeastern United States Birds of South America
cerulean warbler The cerulean warbler (''Setophaga cerulea'') is a small songbird in the family Parulidae. It is a long-distance migrant, breeding in eastern North American hardwood forests. In the non-breeding season, it winters on the eastern slope of the And ...
Taxa named by Alexander Wilson (ornithologist)