American Yellow Warbler

Other than in male breeding plumage and body size, all warbler subspecies 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, the remiges and rectrices are blackish olive with yellow edges, sometimes appearing as an indistinct wing-band on the former. The eyes and the short thin beak are dark, while the feet are lighter or darker olive-buff. The 35 subspecies of D. petechia can be divided into three main groups according to the males' head color in the breeding season. Each of these groups is sometimes considered a separate species, or the aestiva group (yellow warbler) is considered a species different from D. petechia (mangrove warbler, including golden warbler); the latter option is the one currently accepted by the International Ornithological Congress World Bird List. Depending on subspecies, the American 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, the wing 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), the bill is 0.8 to 1.3 cm (0.31 to 0.51 in) and the tarsus is 1.7 to 2.2 cm (0.67 to 0.87 in). 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 name petechia, which roughly translates to "liver spotted". The subspecies in this group mostly vary in brightness and size according to Bergmann's and Gloger's Rule. The golden warbler (petechia group; 17 subspecies) is generally resident in the mangrove swamps of the West Indies. Local seasonal migrations may occur. On the Cayman Islands for example, D. p. eoa was found to be "decidedly scarce" on Grand Cayman and apparently absent from Cayman Brac in November 1979, while it had been a "very common" breeder in the group some 10 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 (D. p. gundlachi) barely reached the Florida Keys where it was first noted in 1941, and by the mid-20th century a breeding population was resident. 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 as little as 6.5 g (0.23 oz). The summer males differs 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. The mangrove warbler (erithachorides group; 12 subspecies) 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; D. p. aureola is found on the oceanic Galápagos Islands. 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. The American yellow warbler (aestiva group; 6 subspecies) breeds in the whole of temperate North America as far south as central Mexico in open, often wet, woods or shrub. It is migratory, wintering in Central and South America. They are very rare vagrants to western Europe.