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==Distribution and habitat==
==Distribution and habitat==


The black-throated blue warblers are a migrant species. They breed in temperate mature [[deciduous]] or [[temperate broadleaf and mixed forest|mixed coniferous-deciduous forest]] with thick [[understory]], often in the hilly and mountainous regions in the northeastern United States and southeastern Canada. <ref name="Cornell"/> At late summer, they migrate to the tropical wooded and scrub habitats in the [[Greater Antilles]] for [[Overwintering|wintering]]. Along their migration, the black-throated blue warblers are observed in habitats like parks and gardens. <ref name="Cornell"/> <ref name=Handbook/>
The Black-throated Blue Warbler is a migratory species. It breeds in temperate mature [[deciduous]] or [[temperate broadleaf and mixed forest|mixed coniferous-deciduous forest]] with thick [[understory]], often in the hilly and mountainous regions in the northeastern United States and southeastern Canada. <ref name="Cornell"/> At late summer, it migrates to the tropical wooded and scrub habitats in the [[Greater Antilles]] for [[Overwintering|wintering]]. Along the migration route, the Black-throated Blue Warbler can be observed in habitats such as parks and gardens. <ref name="Cornell"/> <ref name=Handbook/>
Nesting sites play a more important role in determining the habitat of black-throated blue warblers than foraging sites. <ref name="Steele">{{cite journal|last=Steele|first=B.B.|title=Selection of Foraging and Nesting Sites by Black-Throated Blue Warblers: Their Relative Influence on Habitat Choi|journal=The Condor|year=1993|volume=95|series=3|pages=568-579|accessdate=27 November 2012}}</ref> This is especially significant for an open-nesting species like the black-throated blue warblers.
Nesting sites play a more important role in determining the habitat of the Black-throated Blue Warbler than foraging sites. <ref name="Steele">{{cite journal|last=Steele|first=B.B.|title=Selection of Foraging and Nesting Sites by Black-Throated Blue Warblers: Their Relative Influence on Habitat Choi|journal=The Condor|year=1993|volume=95|series=3|pages=568-579|accessdate=27 November 2012}}</ref> This is especially significant as it is an open-nesting species.{{cn}}


==Behavior==
==Behavior==

Revision as of 09:36, 8 December 2012

Black-throated Blue Warbler
Male
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Aves
Order:
Passeriformes
Family:
Parulidae
Genus:
Setophaga
Species:
S. caerulescens
Binomial name
Setophaga caerulescens
(Gmelin, 1789)
Breeding (green) and wintering (blue) ranges of the Black-throated Blue Warbler.[1]
Synonyms

Dendroica caerulescens

The Black-throated Blue Warbler (Setophaga caerulescens) is a small songbird of the New World warbler family.

Its breeding ranges are located in the interior of deciduous and mixed forests in eastern North America. It builds its nests in thick shrubs and the closeness of its nesting sites to the ground make the Black-throated Blue Warbler a favored species for the study of warbler behavior in the wild.

Black-throated Blue Warblers migrate to islands in the Caribbean and Central America. They defend their territory against other birds of the same species for both nesting and winter habitats. They are very rare vagrants to western Europe.

As Black-throated Blue Warblers require large, unbroken forest areas for nesting, their numbers are declining.

Taxonomy and phylogeny

The German naturalist Johann Friedrich Gmelin described the Black-throated Blue Warbler in 1789. Its species name is the Latin adjective caerulescens "turning blue".

The Black-throated Blue Warbler is one of the New World Warblers or wood-warblers in the family Parulidae. This species was originally placed under the genus Dendroica. It was recently adjusted to be a member of genus Setophaga along with all other members of the genus Dendroica, based on the findings from a recent phylogenetic analysis of mitochondrial DNA and nuclear DNA in 2010.[2] The old genus Dendroica was then deleted.[3] Within the genus it appears to have no particularly close relatives.[2]

The species breeds in North America and winters in the Caribbean. Some studies have observed significant differences in terms of migratory behavior and plumage color between northern and southern populations within the breeding range. [4] The northern population mainly winters in the western Caribbean (Cuba and Jamaica) while the southern population usually spends the winter on eastern islands (Hispaniola and Puerto Rico). 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. 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). [5] 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.[5]

Description

Female

The Black-throated Blue Warbler measures 13 cm (5.1 in) in length and weighs 8.4-12.4 g (0.3-0.45 oz). [6] Adult males have white underparts with black throats, faces and flanks. Their upperparts are deep blue. Immature males are similar, but with greener upperparts. Females have olive-brown upperparts and light yellow underparts with darker wings and tails, gray crowns and brown patches on the cheek. All Black-throated Blue Warblers have thin pointed bills and small white wing patches which are not always visible. Like many warblers, they have colorful plumage during the spring and summer, but their fall plumage is drab and less distinctive. In the fall, they can still be identified from other similar warblers by their small white wing patches. Juveniles have brown upperparts with creamy supercilium and brownish spots on throat, breast and belly. [6]

The bird's song can be described as a buzzed zee-zee-zeeee with an upward inflection. Its call is a flat ctuk.[citation needed]

Distribution and habitat

The Black-throated Blue Warbler is a migratory species. It breeds in temperate mature deciduous or mixed coniferous-deciduous forest with thick understory, often in the hilly and mountainous regions in the northeastern United States and southeastern Canada. [7] At late summer, it migrates to the tropical wooded and scrub habitats in the Greater Antilles for wintering. Along the migration route, the Black-throated Blue Warbler can be observed in habitats such as parks and gardens. [7] [6] Nesting sites play a more important role in determining the habitat of the Black-throated Blue Warbler than foraging sites. [8] This is especially significant as it is an open-nesting species.[citation needed]

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 insects such as caterpillars, crane flies, and spiders. 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 3 and 9 m, females tend to forage at lower strata. [8] The time within a breeding season influences where the males forage. When it’s time to feed the fledglings, males come down to the same foraging strata as females. The black-throated blue warblers mostly forage in the understory instead of the canopy. [9] The large leaves and long branches in the understory affect their foraging behaviors. They more often hover rather than glean the preys because it’s more difficult to glean among thick understory foliage.

Breeding

The Black-throated Blue Warbler is a monogamous species.[10] Its breeding season usually starts in May and ends in July.[11] As a songbird, the male Black-throated Blue Warbler attracts a female’s attention by singing a soft melody. He then follows the steps of 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, extends his head forward and up, opens his bill, and faces the female.[7] The female also makes displays to the male by quivering her wings. In response, the male mounts the female for 2-3 seconds and then flies off.

A 1996 study conducted by Holmes et al. showed that the Black-throated Blue Warbler prefers to reside in hardwood forests 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 is also older, being composed of males and females who are at least two years of age.[12]

The Black-throated Blue Warbler uses social cues in its evaluation and choice of nesting sites.[11] In particular, it listens to the post-breeding songs given out by other males, which have strong temporal dependencies. Males sing at the beginning and the peak of breeding season, but these 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 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 Warblers is a socially monogamous species, males are frequently observed in territories of other males, suggesting the occurrence of extra-pair matings. [10] [13] The parentage of nestlings is identified by microsatellites in a study plot at the Hubbard Brook Experimental Forest in New Hampshire.[14] The result shows that extra-pair fertilization (EPF) does occur and 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 receives evidence from another study conducted earlier, which finds that EPF is strongly and positively correlated with local synchrony but has no significant association with population level synchrony. [10]

Males engage in mate guarding during fertility risk period. 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. [7] The guarding behavior, though, may conflict with males’ pursuit of EPF. It is not yet clear to what extent a male will prefer mate guarding over EPF. [10] 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 EPF attempts. [13] The EPF 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 EPF may incorporate good genes in their offspring, but they are likely to receive less help with parental care from their social mates because of cheating. EPF, therefore, can be costly to females as well.[15] Effort has been made to explain why female black-throated blue warblers engage in extra-pair mating. Popular heterozygosity theories assert that females select males with overall high heterozygosity or dissimilar genetics from themselves.[16][17] A microsatellite study suggests an alternative to heterozygosity selection. Because no correlation is found between female EPF 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.[18]

Sexual selection

Song.
Black-throated blue warblers in Smoky Mountain, North Carolina
Problems playing this file? See media help.

Males’ differential recognition of local and nonlocal songs has been studied in two populations: one in the northern United States (New Hampshire) and the other in the southern United States (North Carolina).[19] 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 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, 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.[20][21][22] A yearling participates in extra-pair mating and cuckoldry 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.[23] Directional asymmetry is present in many passerine birds. The left testicle is most often times larger in size than the right one, and this holds true for both yearling and older male warblers. However, the testicular 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 is ranked as Least Concern by the IUCN in 2012. [24] Deforestation and habitat fragmentation are threatening the black-throated blue warblers in their tropical wintering areas. [25] A report in 2000 discussed the impact of global climate change on the population dynamics of the black-throated blue warblers by an observation from 1986 to 1998. In particular, the effect of El Niño Southern Oscillation (ENSO) was studied in relation to the survival, fecundity and recruitment of this migratory bird. [26] It was found that El Niño years (the warm 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 when the weather was wetter and the food availability was much more abundant. The long-term global warming can aggravate the ENSO effect, adding to the fluctuation of the black-throated blue warbler population. [27]

References

  1. ^ Template:IUCN Database entry includes justification for why this species is of least concern
  2. ^ a b Lovette, Irby J.; et al. (2010). "A comprehensive multilocus phylogeny for the wood-warblers and a revised classification of the Parulidae (Aves)" (PDF). Molecular Phylogenetics and Evolution. 57 (2): 753–70. doi:10.1016/j.ympev.2010.07.018. {{cite journal}}: Explicit use of et al. in: |author= (help)
  3. ^ Chesser, R.T. (2011). "Fifty-second Supplement to the American Ornithologists' Union Check-list of North American Birds". The Auk. 3. 128: 600–613. doi:10.1525/auk.2011.128.3.600. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  4. ^ Rubenstein, D.R. (2002). "Linking breeding and wintering ranges of a migratory songbird using stable isotopes". Science. 295: 1062–1065. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  5. ^ a b Davis, L.A. (2006). "Genetic divergence and migration patterns in a North American passerine bird: implications for evolution and conservation". Molecular Ecology. 15: 2141–2152. doi:10.1111/j.1365-294X.2006.02914.x. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  6. ^ a b c del Hoyo, J.; Elliott, A.; Christie, D. (2010). Handbook of the Birds of the World. Barcelona: Lynx Edicions. pp. 747–748. ISBN 978-84-96553-68-2.{{cite book}}: CS1 maint: multiple names: authors list (link)
  7. ^ a b c d Black-throated Blue Warbler (Dendroica caerulescens), Cornell Lab of Ornithology
  8. ^ a b Steele, B.B. (1993). "Selection of Foraging and Nesting Sites by Black-Throated Blue Warblers: Their Relative Influence on Habitat Choi". The Condor. 3. 95: 568–579. {{cite journal}}: |access-date= requires |url= (help)
  9. ^ Robinson, S.K. (1982). "Foraging Behavior of Forest Birds: The Relationships Among Search Tactics, Diet, and Habitat Structure". Ecology. 6. 63: 1918–1931. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  10. ^ a b c d Chuang, H.C. (1999). "Extrapair Paternity and Local Synchrony in the Black-Throated Blue Warbler" (PDF). The Auk. 116 (3): 726–736. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  11. ^ a b Betts, M.G. (2008). "Social Information Trumps Vegetation Structure in Breeding-Site Selection by a Migrant Songbird" (PDF). Proceedings: Biological Sciences. 275 (1648): 2257–2263. doi:10.1098/rspb.2008.0217. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  12. ^ Holmes, R.T. (1996). "Habitat-specific Demography of Breeding Black-throated Blue Warblers (Dendroica caerulescens): Implications for Population Dynamics" (PDF). Journal of Animal Ecology. 65 (2): 183–195. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  13. ^ a b Chuang-Dobbs, H.C. (2001). "The effectiveness of mate guarding by male black-throated blue warblers". Behavioral Ecology. 12 (5): 541–546. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  14. ^ Webster, M.S. (2001). "Microsatellite identification of extrapair sires in a socially monogamous warbler". Behavioral Ecology. 12 (4): 439–446. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  15. ^ Chuang-Dobbs, H.C. (2001). "Paternity and Parental Care in the Black-throated Blue Warbler". Animal Behaviour. 62: 83–92. doi:10.1006/anbe.2001.1733. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)(subscription required)
  16. ^ Weatherhead, P.J. (1999). "A test of the good-genes-as-heterozygosity hypothesis using red-winged blackbirds". Behavioral Ecology. 10: 619–625. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  17. ^ Tregenza, T. (2000). "Genetic compatibility, mate choice and patterns of parentage: invited review" (PDF). Molecular Ecology. 9: 1013–1027. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  18. ^ Smith, S.B. (2005). "The heterozygosity theory of extra-pair mate choice in birds: a test and a cautionary note". Journal of Avian Biology. 36: 146–154. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)(subscription required)
  19. ^ Colbeck, G.J. (2010). "Asymmetric discrimination of geographical variation in song in a migratory passerine". Animal Behaviour. 80: 311–318. doi:10.1016/j.anbehav.2010.05.013. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)(subscription required)
  20. ^ Rohwer, S. (1980). "Delayed maturation in passerine plumages and the deceptive acquisition of resources". American Naturalist. 115: 400–437. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)(subscription required)
  21. ^ Rohwer, S. (1988). "Winter versus summer explanations of delayed plumage maturation in termperate passerine birds". American Naturalist. 131: 556–572. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  22. ^ Pitcher, T.E. (1998). "Latitudinal variation in testis size in six species of North American songbirds". Canadian Journal of Zoology. 76: 618–622. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)(subscription required)
  23. ^ Graves, G.R. (2004). "Testicular Volume and Asymmetry are Age-Dependent in Black-Throated Blue Warblers". The Auk. 121 (2): 473–485.(subscription required)
  24. ^ [www.iucnredlist.org "Dendroica caerulescens"]. IUCN 2012. IUCN Red List of Threatened Species. BirdLife International. Retrieved 27 November 2012. {{cite web}}: Check |url= value (help)
  25. ^ "Black-throated blue warbler". Arkive. Retrieved 27 November 2012.
  26. ^ Sillett, T.S. (2000). "Impacts of a Global Climate Cycle on Population Dynamics of a Migratory Songbird". Science. 288: 2040–2042. doi:10.1126/science.288.5473.2040. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  27. ^ Kerr, R.A. (1999). "Big El Niños Ride the Back of Slower Climate Change". Science. 5405. 283: 1108–1109. {{cite journal}}: |access-date= requires |url= (help)

Media related to Setophaga caerulescens at Wikimedia Commons

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Bird Call
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