swainson's warbler (limnothlypis swainsonii) is a small species of new world warbler .
it is monotypic , the only member of the genus limnothlypis .
swainson's warbler was named after william swainson , an english ornithologist .
swainson's warblers are a small and rather nondescript songbird , though are fairly large for a new world warbler .
adults grow to 12.516 cm (4.96.3 in) in length and 1120.5 g (0.390.72 oz) in weight .
the wingspan averages 23 cm (9.1 in) .
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 .
swainson's warblers are uncommon , 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 yucatn peninsula region in winter .
this species begins breeding at about 10 months of age (graves in winker et al .
2000) .
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 three and five 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 later .
it is not known how long pairs stay together , although once a pair-bond has been established they do not usually mate with other birds at least in the current nesting season .
these birds live to as old as 8 years (graves in winker et al .
2000) .
no subspecies are recognized .
there appears to be some divergence between populations from arkansas and others of the coastal plains .
this does fit a pattern one would expect from genetic drift , but there seem to be no geographical or ecological barriers restricting gene flow .
even during the last ice age , when average temperatures , precipitation and sea levels were lower , there seems to have been ample contiguous habitat .
clearly , some factor restricting gene flow is at work , but it is not presently known what it is .
it is possible that the subpopulations conform to the different wintering areas .
(winker et al .
2000)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 .
more research such as analyzing bird banding data is needed to determine whether this mechanism applies in swainson's warbler .
