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| Yellow warbler | |
|---|---|
.jpg) | |
| Male, New York, New York | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Passeriformes |
| Family: | Parulidae |
| Genus: | Setophaga |
| Species: | S. petechia |
| Binomial name | |
| Setophaga petechia | |
| Subspecies | |
About 35 (but see text) | |
 | |
| Distribution of the yellow warbler Breeding range Year-round range Wintering range | |
| Synonyms | |
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Theyellow warbler (Setophaga petechia) is aNew World warblerspecies. Yellow warblers are the most widespread species in the diverse genusSetophaga, breeding in almost the whole ofNorth America, theCaribbean, as well as northernSouth America.
The yellow warbler wasformally described in 1766 by the Swedish naturalistCarl Linnaeus in thetwelfth edition of hisSystema Naturae under thebinomial nameMotacilla petechia.[2][3] The specific epithetpetechia is from the Italian wordpetecchia "a small red spot on the skin".[4] Linnaeus based his account on the "yellow-red pole" that had been described and illustrated in 1758 by the English naturalistGeorge Edwards in his bookGleanings of Natural History. Edwards had obtained a specimen from the midwifeSidney Kennon.[5] Edwards was unsure of the provenance of the specimen but in 1935 the Austrian ornithologistCarl Eduard Hellmayr designated the island ofBarbados.[3][6] The yellow warbler is now placed in thegenusSetophaga that was introduced by the English naturalistWilliam Swainson in 1827.[7] The genus nameSetophaga combines theAncient Greekσης/sēs,σητος/sētos meaning "moth" with-φαγος/-phagos meaning "-eating".[8]
Other than in malebreeding plumage and body size, allwarblersubspecies are very similar. Winter, female and immature birds all have similarly greenish-yellow uppersides and are a duller yellow below. Young males soon acquire breast and, where appropriate, head coloration. Females are somewhat duller, most notably on the head. In all, theremiges andrectrices are blackish olive with yellow edges, sometimes appearing as an indistinct wing-band on the former. The eyes and the short thinbeak are dark, while the feet are lighter or darker olive-buff.[9][10]
The 35 subspecies ofS. petechia can be divided into three main groups according to the males' head color in the breeding season.[10] Each of these groups is sometimes considered a separatespecies, or theaestiva group (yellow warbler) is considered a species different fromS. petechia (mangrove warbler, including golden warbler); the latter option is the one currently accepted by theInternational Ornithological CongressWorld Bird List.[11]
Depending on subspecies, the yellow warbler may be between 10 and 18 cm (3.9 and 7.1 in) long, with a wingspan from 16 to 22 cm (6.3 to 8.7 in). They weigh 7–25 g (0.25–0.88 oz), varying between subspecies and whether on migration or not, globally averaging about 16 g (0.56 oz) but only 9–10 g (0.32–0.35 oz) in most breeding adults of the United States populations. Among standard measurements throughout the subspecies, thewing chord is 5.5 to 7 cm (2.2 to 2.8 in), the tail is 3.9 to 5.6 cm (1.5 to 2.2 in), thebill is 0.8 to 1.3 cm (0.31 to 0.51 in) and thetarsus is 1.7 to 2.2 cm (0.67 to 0.87 in).[10] The summer males of this species are generally the yellowest warblers wherever they occur. They are brilliant yellow below and greenish-golden above. There are usually a few wide, somewhat washed-out rusty-red streaks on the breast and flanks. These markings are the reason for the scientific namepetechia, which roughly translates to "liver spotted".[12] The subspecies in this group mostly vary in brightness and size according toBergmann's andGloger's Rule.[13]
Thegolden warbler (petechia group; 17 subspecies[10]) is generally resident in themangrove swamps of theWest Indies. Local seasonal migrations may occur. On theCayman Islands for example,S. p. eoa was found to be "decidedly scarce" onGrand Cayman and apparently absent fromCayman Brac in November 1979, while it had been a "very common" breeder in the group some ten years before, and not frequently seen in the winters of 1972/1973; apparently, the birds disperse elsewhere outside the breeding season. The Cuban golden warbler (S. p. gundlachi) barely reached theFlorida Keys where it was first noted in 1941, and by the mid-20th century a breeding population was resident.[14] Though individual birds may stray farther north, their distribution is restricted by the absence of mangrove habitat.
They are generally smallish, usually weighing about 10 g (0.35 oz) or less and sometimes[15] as little as 6.5 g (0.23 oz). The summer males differ from those of the yellow warbler in that they have a rufous crown, hood or mask. The races in this group vary in the extent and hue of the head patch.
Themangrove warbler (erithachorides group; 12 subspecies[10]) tends to be larger than other yellow warbler subspecies groups, averaging 12.5 cm (4.9 in) in length and 11 g (0.39 oz) in weight. It is resident in the mangrove swamps of coastal Middle America and northern South America;S. p. aureola is found on the oceanicGalápagos Islands.[10] The summer males differ from those of the yellow warbler in having a rufous hood or crown. The races in this group vary in the extent and hue of the hood, overlapping extensively with the golden warbler group in this character.[10]
TheAmerican yellow warbler (aestiva group; 6 subspecies)[10] breeds in the whole oftemperateNorth America as far south as central Mexico in open, often wet, woods or shrub. It ismigratory, wintering inCentral and South America. They are very rare vagrants to westernEurope[9] andScandinavia[16]
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The song is a musical strophe that can be renderedsweet sweet sweet, I'm so sweet, although it varies considerably betweenpopulations. The call is a soft or harderchip orship. This is particularly frequently given by females after a male has finished his song. Interritorial defense, they give hissing calls, whileseet seems to be a kind of specializedcowbird alert (see below). Other calls are given in communication between pair-members, neighbors, or by young begging for food. These birds also communicate with postures and perhaps with touch.[9]
American yellow warblers breed in most ofNorth America from thetundra southwards, except for the far Southwest and theGulf of Mexico coast.[9] American yellow warblers winter to the south of their breeding range, from southernCalifornia to theAmazon region,Bolivia andPeru.[9] The mangrove and golden warblers occur to the south of it, to the northern reaches of theAndes.
American yellow warblers arrive in their breeding range in late spring – generally about April/May – and move to winter quarters again starting as early as July, as soon as the young are fledged. Most, however, stay a bit longer; by the end of August, the bulk of the northern populations has moved south, though some may linger almost until fall. At least in northernOhio, yellow warblers do not linger, leaving as they did 100 years ago.[17]
The breeding habitat of American yellow warblers is typicallyriparian or otherwise moist land with ample growth of small trees, in particularwillows (Salix). The other groups, as well as wintering birds, chiefly inhabitmangrove swamps and similar dense woody growth. Less preferred habitats areshrubland,farmlands andforest edges. In particular American yellow warblers will come tosuburban or less densely settled areas,orchards andparks, and may well breed there. Outside the breeding season, these warblers are usually encountered in small groups, but while breeding they are fiercelyterritorial and will try to chase away anyconspecific intruder that comes along.[9]
Roughly 60% of their diet is caterpillars. They also consume wasps,[18] mayflies, moths, mosquitoes, beetles, damselflies, treehoppers, other insects,[19] insect larvae, and spiders.[20] They acquire prey bygleaning in shrubs and on tree branches, and byhawking prey that tries to fly away. Otherinvertebrates and someberries and similar small juicyfruits[21] are also eaten, the latter especially by American yellow warblers in their winter quarters. The yellow warbler is one of several insectivorous bird species that reduce the number ofcoffee berry borer beetles in Costa Rica coffee plantationsby 50%.Caterpillars are the staple food fornestlings, with some – e.g. those ofgeometer moths (Geometridae) – preferred over others.[22]
Thepredators of yellow and mangrove warblers are those typical of such smallish tree-nestingpasserines, such assnakes,foxes,birds of prey, and many others. The odds of an adult American yellow warbler surviving from one year to the next are on average 50%; in the southern populations, by contrast, about two-thirds of the adults survive each year. Conversely, less than one American yellow warbler nest in three on average suffers from predation in one way or another, while two out of three mangrove and golden warbler nests are affected.[23]
Snakes, including theblue racer (Coluber constrictor foxii) andcommon garter snake (Thamnophis sirtalis),[24] are significant nest predators, takingnestlings andfledglings as well as sick or distracted adults. Likewise,corvids such as theAmerican crow (Corvus brachyrhynchos) andblue jay (Cyanocitta cristata),[25] and large climbingrodents, notably theAmerican red squirrel (Tamiasciurus hudsonicus) also attack nests in this manner.[25]Carnivores (in particular members of theMusteloidea) including thestriped skunk (Mephitis mephitis),long-tailed weasel (Neogale frenata),common raccoon (Procyon lotor),[9]red fox (Vulpes vulpes), anddomestic orferal cats, are similarly opportunistic predators. All these pose little threat to the nimble, non-nesting adults, which are taken by certain smallish and agile birds such as theAmerican kestrel (Falco sparverius) andCooper's hawk (Accipiter cooperii), and thesharp-shinned hawk (A. striatus). Other avian predators of adults have includedperegrine falcons (Falco peregrinus) andmerlins (F. columbarius). Owls such asgreat horned owls (Bubo virginianus) andeastern screech owls (Megascops asio) have been known to assault yellow warblers of all ages at night.[9][26]
These New World warblers seem tomob predators only rarely. An exception arecowbirds, which are significantbrood parasites. The yellow warbler is a regular host of thebrown-headed cowbird (Molothrus ater), with about 40% of all nests suffering attempted or successful parasitism. By contrast, the tropical populations are less frequent hosts to theshiny cowbird (M. bonariensis), with only 10% of nests affected. This may be due to the slightly larger size of shiny cowbirds, which are less likely to survive being fed by the much smaller warbler, compared to brown-headed cowbirds.[26] The yellow warbler is one of the few passerine proven to be able to recognize the presence of cowbird eggs in its nest.[26] Upon recognizing one the warbler will often smother it with a new layer of nesting material. It will usually not try to save any of its own eggs that have already been laid, but produce a replacementclutch. Sometimes, the parents desert a parasitized nest altogether and build a new one. Unlike somecuckoos, cowbird nestlings will not actively kill the nestlings of the host bird; mixed broods ofSetophaga andMolothrus mayfledge successfully.[23] However, success of fledging in yellow warbler nests is usually decreased by the parasitism of cowbirds due to the pressures of raising a much larger bird.[26]
Other than predation, causes ofmortality are not well known. The maximum recorded ages[27] of wild yellow warblers are around 10 years. A wintering American yellow warbler examined nearTurbo, Colombia was not infected with bloodparasites, unlike other species in the study. It is unclear whether this significant, but wintering birds in that region generally lacked such parasites.[28]
As usual for members of theParulidae, yellow warblers nest in trees, building a small but very sturdy cup nest. Females and males rear the young about equally, but emphasize different tasks: females are more involved with building and maintaining the nest, and incubating and brooding the offspring. Males are more involved in guarding the nest site and procuring food, bringing it to the nest and passing it to the waiting mother, which does most of the actual feeding. As the young approachfledging, the male's workload becomes proportionally higher.[9]
_in_Waterville%2c_Maine.jpg)
The American yellow and mangrove (including golden) warblers differ in some other reproductive parameters. While the former is somewhat more of anr-strategist, the actual differences are complex andadapted to different environmental conditions. The yellow warbler starts breeding in May/June, while the mangrove warbler breeds all year round. American yellow warblers have been known to raise a brood of young in as little as 45 days, with 75 the norm.Tropical populations, by contrast, need more than 100 days per breeding. Males court the females with songs, singing 3,200 or more per day. They are, like mostsongbirds, generallyserially monogamous; some 10% of mangrove warbler and about half as many American yellow warbler males are bigamous. Very few if any American yellow warblers breed more than once per year, with just 5% of female mangrove warblers doing so. If a breeding attempt fails, either parent will usually try to raise a second brood.[23]
Theclutch of the American yellow warbler is 3–6 (typically 4–5, rarely 1–2) eggs.Incubation usually takes 11 days, sometimes up to 14. Thenestlings weigh 1.3 g (0.046 oz) on average, arebrooded for an average 8–9 days after hatching, and leave the nest the following day or the one thereafter. The mangrove warbler has only 3 eggs per clutch on average and incubates some 2 days longer. Its average post-hatching brooding time is 11 days. Almost half of the parents (moreso in the mangrove warbler than the American yellow warbler) attend the fledglings for two weeks or more after these leave the nest. Sometimes the adults separate early, each accompanied by one to three of the young.[29]
Some 3–4 weeks after hatching, the young are fully independent of their parents. They becomesexually mature at one year of age, and attempt to breed right away. Some 55% of all American yellow warbler nestings are successful in raising at least one young.[29] In contrast, only 25% of mangrove warbler nests successfully fledge any offspring, with accidents andpredation frequently causing total loss of the clutch.
Yellow warblers, in particular the young, devour manypestinsects during the breeding season. The plumage and song of the breeding males have been described[9] as "lovely" and "musical". No significant negative effects of American yellow and mangrove warblers on humans have been recorded.[9]
Being generally common and occurring over a wide range, the yellow warbler is not considered athreatened species by theIUCN.[30] Some local decline in numbers has been found in areas, mainly due tohabitat destruction andpollution. The chief causes are land clearance, theagricultural overuse of andherbicide andpesticide, and sometimesovergrazing. However, stocks will usually rebound quickly ifriparian habitat is allowed to recover, particularly among the prolific American yellow warbler.[1][9]
TheNorth American populations are legally protected by theMigratory Bird Treaty Act. TheBarbados golden warbler[31] (D. p. petechia) has been listed as "endangered foreign wildlife" by the United States'Endangered Species Act (ESA) since 1970; other than for specially permitted scientific, educational or conservation purposes, importing it into the US is illegal. The Californian yellow warbler (D. p./a. brewsteri) and Sonoran yellow warbler (D.p./a. sonorana) are listed as "species of concern" by the ESA.[32]
