the cerulean warbler (setophaga cerulea) is a small songbird of the new world warbler family .
adult males have pale cerulean blue and white upperparts with a black necklace across the breast and black streaks on the back and flanks .
females and immature birds have greyer or greenish upperparts , a pale stripe over the eye , and no streaking on the back and no neck .
all of these birds have wing bars and a thin pointed bill .
they are found in deciduous forests of eastern north america during the breeding season and then migrate to forested mountain areas in south america .
the species is considered threatened with an iucn status of vulnerable (vu), indicating it is considered to be facing a high risk of extinction in the wild .
adult males have pale cerulean blue upperparts and white underparts with a black necklace across the breast; they also have black streaks on the back and flanks .
females and immature birds have greyer or greenish upperparts , a pale stripe over the eye , and no streaking on the back and no necklace .
all of these birds , regardless of their age , have wing bars and a thin pointed bill .
their breeding habitats are mature deciduous forests in eastern north america .
they migrate to spend the boreal winter in forested mountain areas in south america .
they forage actively high in trees , sometimes catching insects in flight .
these birds mainly eat insects .
their nests are cup-shaped , and are placed on a horizontal branch high in a hardwood tree .
the song is a buzzed zray zray zray zray zeeee .
the call is a slurred chip .
the cerulean warbler is the fastest declining neotropical migrant songbird .
among the many threats they face , their wintering habitat in the northern andes is dwindling rapidly .
cerulean warblers depend on shade coffee plantations during the winter .
this traditional farming technique is at risk as coffee prices fluctuate and pressure to switch to higher-yield sun coffee or other crops intensifies .
in fragmented forest areas , this bird is vulnerable to nest parasitism by the brown-headed cowbird .
this bird's numbers are declining faster than any other warbler species in the usa; its population nowadays is less than one-fifth of what it was 40 years ago  .
the american bird conservancy (abc) is working with its colombian partner , fundacin proaves , to protect wintering habitat for cerulean warblers and other migrating songbirds .
together they have created the cerulean warbler bird reserve , the first protected area created for a neotropical migrant .
in an effort to advance protection of the cerulean warbler , abc and its south american partners (fundacion proaves , ecoan and fundacion jocotoco), in 2009 produced a cerulean warbler wintering ground conservation plan .
the cerulean warbler has been recorded as a vagrant to iceland .
