0 the warbling vireo (vireo gilvus) is a small north american songbird .
1 its breeding habitat is open deciduous and mixed woods from alaska to mexico and the florida panhandle .
2  it often nests along streams .
3  it migrates to mexico and central america .
4 adults are 12 cm (4.7 in) long and weigh 12 g (0.42 oz) .
5  they are mainly olive-grey on the head and upperparts with white underparts; they have brown eyes and the front of the face is light .
6  there is a white supercilium .
7  they have thick blue-grey legs and a stout bill .
8  western birds are generally smaller and have darker grey crowns .
9 warbling vireos forage for insects in trees , hopping along branches and sometimes hovering .
10  they also eat berries , especially before migration and in winter quarters , where they are  like other vireos  apparently quite fond of gumbo-limbo seeds , though they will not venture into human-modified habitat to get them .
11  they make a deep cup nest suspended from a tree branch or shrub , placed relatively high in the east and lower in the west .
12  the male helps with incubation and may sing from the nest .
13 the warbling vireo's song is a cheerful warble , similar to that of the painted bunting .
14  there are subtle differences in song between eastern and western birds , at least where the ranges meet in alberta .
15  some authorities split the eastern and western races of this species into separate species: the western warbling vireo , v .
16  swainsoni , includes v .
17  g .
18  swainsoni , which breeds from southeastern alaska and southwestern northwest territories to the sierra san pedro mrtir , baja california , and v .
19  g .
20  brewsteri , which breeds from southern idaho , wyoming , and montana to south-central oaxaca .
21  these two subspecies winter in mexico .
22  the swainsoni group also includes v .
23  g .
24  victoriae , an isolated population breeding in the sierra de la laguna , baja california sur , and migrating to unknown wintering grounds .
25 the eastern warbling vireo , v .
26  gilvus , breeds from central alberta and northern montana east and south through most of the united states and parts of southern canada , outside the range of the previous group .
27  it winters south of the isthmus of tehuantepec from south-central chiapas to nicaragua .
28  it completes its autumn molt on the breeding grounds , while the swainsonii group completes it after leaving .
29 the brown-capped vireo (vireo leucophrys), resident in central america and northern south america , is sometimes considered conspecific with the warbling vireo .
