The black-throated blue warbler (''Setophaga caerulescens'') is a small
passerine
A passerine () is any bird of the order Passeriformes (; from Latin 'sparrow' and '-shaped'), which includes more than half of all bird species. Sometimes known as perching birds, passerines are distinguished from other orders of birds by t ...
bird of the
New World warbler
The New World warblers or wood-warblers are a group of small, often colorful, passerine birds that make up the family Parulidae and are restricted to the New World. They are not closely related to Old World warblers or Australian warblers. Most ...
family. Its breeding ranges are located in the interior of
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, aft ...
and
mixed coniferous forest
Mixed coniferous forest is a vegetation type dominated by a mixture of broadleaf trees and conifers.Sierra Nevada Wildflowers, Karen Wiese, 2nd ed, 2013, p 13–14 It is generally located in mountains, below the upper montane vegetation type.
Si ...
s in eastern
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
. Over the cooler months, it
migrates to islands in the
Caribbean
The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean Se ...
and
Central America
Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...
. It is very rarely found in western
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
, where it is considered to be a non-indigenous species. The black-throated blue warbler is sexually dimorphic; the adult male has a black face and cheeks, deep blue upperparts and white underparts, while the adult female is olive-brown above and light yellow below.
Predominantly
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 ...
, the black-throated blue warbler supplements its diet with berries and seeds in winter. It builds its nests in thick shrubs and the closeness of its nesting sites to the ground make it a favored species for the study of warbler behavior in the wild. The black-throated blue warbler defends its territory against other birds of the same species for both nesting and winter habitats. As the black-throated blue warbler requires large, unbroken forest areas for nesting, its numbers are declining.
Taxonomy and phylogeny
The German naturalist
Johann Friedrich Gmelin
, fields =
, workplaces = University of GöttingenUniversity of Tübingen
, alma_mater = University of Tübingen
, doctoral_advisor = Philipp Friedrich GmelinFerdinand Christoph Oetinger
, academic_advisors =
, doctora ...
described the black-throated blue warbler in 1789. Its species name is the
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
adjective ''caerulescens'' meaning "turning blue".
The black-throated blue warbler is one of the New World warblers or wood-warblers in the family
Parulidae
The New World warblers or wood-warblers are a group of small, often colorful, passerine birds that make up the family Parulidae and are restricted to the New World. They are not closely related to Old World warblers or Australian warblers. Most ...
. This species was originally placed under the genus ''Dendroica''. It was recently adjusted to be a member of 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 ...
'' along with all other members of the genus ''Dendroica'', based on the findings from a recent
phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
analysis of
mitochondrial DNA
Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...
and
nuclear DNA
Nuclear DNA (nDNA), or nuclear deoxyribonucleic acid, is the DNA contained within each cell nucleus of a eukaryotic organism. It encodes for the majority of the genome in eukaryotes, with mitochondrial DNA and plastid DNA coding for the rest. It ...
in 2010.
The old genus ''Dendroica'' was then deleted. Within the genus, it appears to have no particularly close relatives.
[
The species breeds in North America and winters in the ]Caribbean
The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean Se ...
. Some studies have observed significant differences in terms of migratory behavior and plumage color between northern and southern populations within the breeding range. The northern population mainly winters in the western Caribbean (Cuba
Cuba ( , ), officially the Republic of Cuba ( es, República de Cuba, links=no ), is an island country comprising the island of Cuba, as well as Isla de la Juventud and several minor archipelagos. Cuba is located where the northern Caribbea ...
and Jamaica
Jamaica (; ) is an island country situated in the Caribbean Sea. Spanning in area, it is the third-largest island of the Greater Antilles and the Caribbean (after Cuba and Hispaniola). Jamaica lies about south of Cuba, and west of His ...
) while the southern population usually spends the winter on eastern islands (Hispaniola
Hispaniola (, also ; es, La Española; Latin and french: Hispaniola; ht, Ispayola; tnq, Ayiti or Quisqueya) is an island in the Caribbean that is part of the Greater Antilles. Hispaniola is the most populous island in the West Indies, and th ...
and Puerto Rico
Puerto Rico (; abbreviated PR; tnq, Boriken, ''Borinquen''), officially the Commonwealth of Puerto Rico ( es, link=yes, Estado Libre Asociado de Puerto Rico, lit=Free Associated State of Puerto Rico), is a Caribbean island and Unincorporated ...
). Moreover, males in the southern population have darker plumage than those in the northern population. These differences have led biologists to consider them as separate subspecies
In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...
. However, a recent study in the United States reveals no significant genetic differentiation between northern (samples from Michigan, New Hampshire and New York states) and southern populations (sample from North Carolina). The study results actually show a recent population expansion from a single glacial refugium, therefore the current populations are homogeneous in terms of genetics. The differentiation that is observed between the northern and southern populations should have occurred quite recently.[
]
Description
The black-throated blue warbler measures in length and weighs . Wingspan ranges from 7.5-7.9 in (19-20 cm). This is a strongly sexually dimorphic
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 ...
bird. The adult male has white underparts with a black throat, face and flanks. The upperparts are deep blue. The immature male is similar, but with greener upperparts. The female has olive-brown upperparts and light yellow underparts with darker wings and tail, gray crown and brown patches on the cheek. Both sexes have a thin pointed bill and small white wing patches which are not always visible. Like many other warbler species, it has colorful plumage
Plumage ( "feather") is a layer of feathers that covers a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage differ between species and subspecies and may vary with age classes. Within species, ...
during the spring and summer. However, outside the breeding season its plumage is drab and less distinctive. In the fall, the black-throated blue warbler can be distinguished by its small white wing patches. Juveniles have brown upperparts with a creamy 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 ...
and brownish spots on the throat, the breast and the belly.[
The bird's ]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 repetitio ...
can be described as a buzzed ' with an upward inflection. Its call is a flat '.[
]
Distribution and habitat
The black-throated blue warbler is a migratory species. It breeds in temperate 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, aft ...
forests or mixed coniferous-deciduous forest with a thick understory
In forestry and ecology, understory (American English), or understorey (Commonwealth English), also known as underbrush or undergrowth, includes plant life growing beneath the forest canopy without penetrating it to any great extent, but abov ...
. The species is often found in hilly and mountainous regions in the northeastern United States and southeastern Canada. In late summer, it migrates to the tropical wooded and scrub habitats in the Greater Antilles
The Greater Antilles ( es, Grandes Antillas or Antillas Mayores; french: Grandes Antilles; ht, Gwo Zantiy; jam, Grieta hAntiliiz) is a grouping of the larger islands in the Caribbean Sea, including Cuba, Hispaniola, Puerto Rico, Jamaica, and ...
for wintering
Winter is the coldest season of the year in Polar regions of Earth, polar and temperate climates. It occurs after autumn and before spring (season), spring. The tilt of Axial tilt#Earth, Earth's axis causes seasons; winter occurs when a Hemi ...
. Along the migration route, the black-throated blue warbler can be observed in habitats such as parks and gardens.
Its nesting site is more important than its foraging site in playing a role in determining the habitat of the black-throated blue warbler. The black-throated blue warbler is an open-nesting species, that nests very close to the ground so it has to choose a protected nesting site where the risk of predation is relatively low.
Behavior
Feeding and foraging
The black-throated blue warbler forages actively in low vegetation, sometimes hovering or catching insects in flight. It often forages in one area for a while before moving on to the next. It mainly eats invertebrates such as caterpillar
Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths).
As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder Sym ...
s, crane flies
Crane fly is a common name referring to any member of the insect family Tipulidae. Cylindrotominae, Limoniinae, and Pediciinae have been ranked as subfamilies of Tipulidae by most authors, though occasionally elevated to family rank. In the most ...
, and spider
Spiders ( order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...
s. It may supplement its diet with seeds, berries, and fruit in the winter.[
Males and females prefer different foraging sites. While males usually hover among the higher shrub foliage between , females tend to forage at lower strata.] The time within a breeding season influences where the males forage. When it is time to feed the fledglings, males come down to the same foraging strata as females.
The black-throated blue warbler mostly forages in the understory instead of the canopy. The large leaves and long branches in the understory affect its foraging behaviors. The black-throated blue warbler more often hovers rather than gleans its prey because it is more difficult to glean among thick understory foliage.[
]
Breeding
The black-throated blue warbler is a monogamous
Monogamy ( ) is a form of Dyad (sociology), dyadic Intimate relationship, relationship in which an individual has only one Significant other, partner during their lifetime. Alternately, only one partner at any one time (Monogamy#Serial monogamy, ...
species. Its breeding season usually begins in May and ends in July. As a 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 500 ...
, the male black-throated blue warbler attracts a female's attention by singing a soft melody. He then follows the female while she is foraging or searching for nesting sites. As soon as the female stops to rest, the male droops his wings slightly, stretches his head forward and up, opens his bill, and faces the female. The female also makes displays to the male by vibrating her wings. In response, the male mounts the female for 2–3 seconds and then flies off.
A 1996, researchers showed that the black-throated blue warbler prefers to reside in hardwood forests
Temperate broadleaf and mixed forest is a temperate climate terrestrial habitat type defined by the World Wide Fund for Nature, with broadleaf tree ecoregions, and with conifer and broadleaf tree mixed coniferous forest ecoregions.
These f ...
with higher shrub densities where food is more abundant compared to lower shrub density plots. Within these high shrub density habitats, not only is there a higher density of warblers, but the population age average is also older, being composed of males and females who are at least two years of age.
The black-throated blue warbler uses social cues in its evaluation and choice of nesting sites. In particular, it listens to the post-breeding songs given out by other males. These songs have strong temporal dependencies. Males sing at the beginning and the peak of breeding season, but songs are not indicative of reproductive success. Near the end of a breeding season, a male that has successfully mated continues to sing while a male that has failed to reproduce abandons the habitat. Therefore, post-breeding songs are reliable indicators of reproductive success within the particular habitat and convey essential information to the natal and breeding dispersers. In comparison to the traditional idea of direct assessment of the vegetation structure, the vocal cue is much more efficient and easier to obtain, hence revealing the advantage of social communication
Communication (from la, communicare, meaning "to share" or "to be in relation with") is usually defined as the transmission of information. The term may also refer to the message communicated through such transmissions or the field of inquir ...
in survival and reproduction. A female, however, does not respond to post-breeding songs directly. Instead, she is likely to rely on the presence of males in deciding nesting sites.
Extra-pair mating
Although the black-throated blue warbler is a socially monogamous species, males are frequently observed in territories of other males, suggesting the occurrence of extra-pair matings. Nestling parentage is identified by microsatellites
A microsatellite is a tract of repetitive DNA in which certain DNA motifs (ranging in length from one to six or more base pairs) are repeated, typically 5–50 times. Microsatellites occur at thousands of locations within an organism's genome. ...
in a study plot at the Hubbard Brook Experimental Forest
Hubbard Brook Experimental Forest is an area of land in the towns of Woodstock, Ellsworth and Thornton in the White Mountains of New Hampshire that functions as an outdoor laboratory for ecological studies. It was initially established in 1955 ...
in New Hampshire. The results show that extra-pair fertilization occurs and that the majority of the extra-pair sires come from males in neighboring territories. Only very few extra-pair sires are from distant territories. This local reproductive interaction is also supported by another study conducted earlier, which finds that extra pair fertilizations are strongly and positively correlated with local synchrony but there is no significant association with population level synchrony.
Males engage in mate guarding during the period females are most vulnerable to successful extra pair copulations. They usually stay close to their social mate, singing slowly on the side and following the mate while she is foraging or searching for a nesting site. The guarding behavior, though, may conflict with males' pursuit of extra-pair fertilizations. It is not yet clear to what extent a male will prefer mate guarding over extra-pair fertilizations. Male retention studies have shown that removal of a male increases the chance of extra-pair offspring in the brood, suggesting that mate guarding reduces extra-pair fertilization attempts. The extra-pair fertilization rate nonetheless cannot be eliminated even if males are allowed to stay near their social mates during fertility risk period. Several hypotheses try to explain this phenomenon: females may be able to manage extra-pair mating even while its social mate is guarding it, or females may reject extra-pair copulation attempts by other males in the absence of male guarding.
Females who participate in extra-pair fertilizations may incorporate better genes in their offspring than they could get with their social mate, but they are likely to receive less help with parental care from their social mates because of cheating. Extra-pair fertilization, therefore, can be costly to females as well. A possible theory why extra-pair fertilization occurs is that female organisms select males with overall high heterozygosity
Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism.
Mo ...
or dissimilar genetics from themselves. A microsatellite
A microsatellite is a tract of repetitive DNA in which certain DNA motifs (ranging in length from one to six or more base pairs) are repeated, typically 5–50 times. Microsatellites occur at thousands of locations within an organism's genome. ...
study suggests an alternative to heterozygosity selection. Because no correlation is found between female extra-pair fertilization frequencies and the overall heterozygosity of their social mates, it is suggested that females may choose only a selective set of heterozygous genes, particularly the MHC locus, which can affect the immunocompetence of offspring.
Sexual selection
Males' differential recognition of local and nonlocal songs has been studied in two populations: one in the northern United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
(New Hampshire
New Hampshire is a U.S. state, state in the New England region of the northeastern United States. It is bordered by Massachusetts to the south, Vermont to the west, Maine and the Gulf of Maine to the east, and the Canadian province of Quebec t ...
) and the other in the southern United States (North Carolina
North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia and So ...
). An asymmetry of response has been found between the two populations. The northern black-throated blue warbler responds strongly to local songs but relatively weakly to the song of southern warblers. In contrast, a warbler from the south responds equally to songs from both the north and the south. A potential explanation of this asymmetry is the difference in female preference between the northern and southern black-throated blue warblers. Females from the north are less likely to mate with a "heterospecific" male from the south; therefore it is not necessary for a northern male to respond strongly to the song of a southern challenger. It is possible that a barrier to gene flow
In population genetics, gene flow (also known as gene migration or geneflow and allele flow) is the transfer of genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent a ...
from south to north exists while a barrier to the reverse does not. Therefore, female choice of male songs is likely to play a role in gene flow and reproductive isolation
The mechanisms of reproductive isolation are a collection of evolutionary mechanisms, behaviors and physiological processes critical for speciation. They prevent members of different species from producing offspring, or ensure that any offspring ...
, which may eventually lead to diversification.[
It has long been believed that a male black-throated blue warbler achieves reproductive maturation well into its first breeding season. A yearling participates in ]extra-pair mating
Extra-pair copulation (EPC) is a mating behaviour in Monogamy in animals, monogamous species. Monogamy is the practice of having only one sexual partner at any one time, forming a long-term bond and combining efforts to raise offspring together; ma ...
and cuckold
A cuckold is the husband of an adulterous wife; the wife of an adulterous husband is a cuckquean. In biology, a cuckold is a male who unwittingly invests parental effort in juveniles who are not genetically his offspring. A husband who is aw ...
ry as much as or even more than older males. However, research by Graves has found opposing evidence in terms of testicular size and sperm production. Directional asymmetry is present in many passerine bird
A passerine () is any bird of the order Passeriformes (; from Latin 'sparrow' and '-shaped'), which includes more than half of all bird species. Sometimes known as perching birds, passerines are distinguished from other orders of birds by t ...
s. The left testicle is often larger in size than the right one, and this holds true for both yearling and older male warblers. However, the testicle to body mass ratio nonetheless is much lower in yearlings than in older males. Moreover, older males have a greater degree of directional asymmetry than do yearlings. Because the size of testes in birds is correlated to the ejaculate quality, it is likely that females employ age-dependent choice in favor of older males who can be distinguished by their definitive age-specific plumage.[
]
Status and threats
The black-throated blue warbler enjoys a large range and a big population. Its population trend is currently increasing. This species was ranked as Least Concern
A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. T ...
by the IUCN in 2012. 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 d ...
and habitat fragmentation
Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological processes ...
are threatening the black-throated blue warbler in its tropical wintering areas. A report in 2000 discussed the impact of global climate change on the population dynamics of the black-throated blue warbler by an observation from 1986 to 1998. In particular, the effect of El Niño Southern Oscillation
EL, El or el may refer to:
Religion
* El (deity), a Semitic word for "God"
People
* EL (rapper) (born 1983), stage name of Elorm Adablah, a Ghanaian rapper and sound engineer
* El DeBarge, music artist
* El Franco Lee (1949–2016), American po ...
(ENSO) was studied in relation to the survival, fecundity
Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility, the natural capability to pr ...
and recruitment of this migratory bird. It was found that El Niño years (the warm South Pacific oceanic phase) were associated with lower adult survival rate in their wintering ground, Jamaica, lower fecundity in the breeding habitats in New Hampshire of the United States, and lower annual recruitment of yearlings and juveniles to both breeding and wintering grounds. All the three factors were relatively higher during La Niña years (cold South Pacific Ocean) when the weather was wetter and the food availability was much more abundant. Long-term global warming
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
can aggravate the ENSO effect, adding to the fluctuation of the black-throated blue warbler population.
References
External links
Vocals
- USGS
– USGS Patuxent Bird Identification InfoCenter
– Cornell Lab of Ornithology
at bird-stamps.org
*
*
{{Taxonbar, from=Q27075926
black-throated blue warbler
The black-throated blue warbler (''Setophaga caerulescens'') is a small passerine bird of the New World warbler family. Its breeding ranges are located in the interior of deciduous and mixed coniferous forests in eastern North America. Over the ...
Native birds of Eastern Canada
Native birds of the Northeastern United States
Birds of Appalachia (United States)
Birds of the Dominican Republic
black-throated blue warbler
The black-throated blue warbler (''Setophaga caerulescens'') is a small passerine bird of the New World warbler family. Its breeding ranges are located in the interior of deciduous and mixed coniferous forests in eastern North America. Over the ...
Taxa named by Johann Friedrich Gmelin