Swainson’s Warbler

Swainson’s Warbler (Limnothlypis swainsonii), is a small species of New World warbler. It is monotypic, the only member of the genus Limnothlypis. They are an uncommon species, mostly found in flooded swamplands and canebrakes of the south-eastern United States. More rarely, they will also occur in rhododendron thickets in the southern Appalachian mountains. They are a migratory species, with part of the population migrating southeastwards to the Greater Antilles and the other southwestwards to the Yucatán Peninsula region in winter.

Swainson’s Warblers will grow to about 5 to 6½ inches in length and 0.53 ounces in weight. They are a plain olive-brown above and pale yellow-white below. They have a whitish eyebrow stripe that runs above their eye, and the top of their head is a rusty brown. Unlike most other New World warblers that are mostly dimorphic, there is no difference in appearance between a male or female Swainson’s warbler.

This species begins breeding at about 10 months of age. Pairs form and stake out and defend a territory for nesting. Nests are fairly large and bulky, constructed from moss, grass, and small leaves situated above ground in a tangle of tall reeds or vines. The female will lay between 3 to 5 eggs. The eggs are white and sometimes, but rarely, speckled with brown. Incubation is done by the female only and lasts for about 14 days, after which the eggs will hatch. The young leave the nest about 12 days after they have hatched.

In some migrant birds, it is known that the initial direction of the migration is set by fairly simple hereditary mechanisms. Offspring of pairs comprising birds of different subpopulations will, in such species, attempt to migrate into an intermediate direction. Such a course would lead a Swainson’s Warbler deep into the Caribbean where there are no wintering or even stopover points, and the bird would almost certainly perish.