Known as “feathered gems” or “butterflies of the bird world,” the 115 species of wood warblers are all found in the Western Hemisphere. The males in spring are easily identified as they are distinctively garbed mainly in yellows, olives or blue-grays. Most species also have black (or more rarely chestnut red) patches or stripes on the head or breast. Fall birds, especially the young, are much more difficult to identify. The territorial songs of the males are also distinctive: some are staccato, others are high pitched and sibilant, while a few are loud and ringing. The call notes which are made by all birds are mostly simple chips. Saskatchewan has records of thirty-two species.
The group is found in the greatest variety in southeastern Canada and the northeastern United States, where over thirty species may be found. Numbers decline to the north, south and west, but almost twenty-five species may be found in the band of mixedwood forest that crosses central Saskatchewan. Species drop out one by one to the north and east, so that the only species that reach the extreme northeastern corner are the Tennessee, yellow, yellow-rumped, blackpoll and Wilson's warblers, the northern waterthrush, and the common yellowthroat. Similarly, the number of species declines as one travels to the south and west: in many areas south of the aspen parkland the only breeding species are the ubiquitous yellow warbler and the common yellowthroat.
The appearance of the most aberrant of warblers, the yellow-breasted chat, compensates to some extent the loss of species richness in southern Saskatchewan. Huge by warbler standards, the chat is a denizen of the brush tangles and thickets of the province's southern watercourses, and is particularly abundant along the South Saskatchewan and Souris rivers. The high altitude lodgepole pine, aspen and spruce forest of the Cypress Hills attracts birds that would otherwise be found much further north: the Tennessee and orange-crowned warblers, the American redstart, and the ovenbird. The Cypress Hills is the only area where one may expect to see mountain species such as MacGillivray's warbler and Audubon's warbler (the mountain race of the yellow-rumped warbler).
Warblers vary tremendously in the habitats they select. Yellow warblers may be found in almost any type of shrubbery and forest edge, and are the only species that regularly nests in farmsteads, towns and cities; and yellow-rumped warblers nest in almost any type of forest. It is no surprise that these two species are the most abundant in Saskatchewan. Other species are much more particular. Stands of mature mixedwood forest are favoured by so many species that the trees themselves are partitioned amongst them. Many species favour thickets along watercourses, but the only species to nest in marshes is the common yellowthroat.
Warblers are almost exclusively insect-eaters. Most are gleaners, capturing insects off the leaves and twigs or, in the case of the black-and-white warbler, tree limbs and trunks. The Wilson's and Canada warblers, as well as the American Redstart, capture most of their food on the wing. The most specific food requirements belong to the Tennessee, Cape May, and bay-breasted warblers, which are so closely tied to the spruce budworm that their numbers explode in response to budworm outbreaks and decline sharply thereafter. Warblers lay four to seven whitish eggs, usually with dark markings; nests are placed in a tree, a shrub, or more rarely on the ground.
During migration many species of warblers, especially those in breeding in mature mixedwood forests, migrate in a northwest-southeast direction and thus are rare at that time in the southwestern corner of the province. Most other species are frequently seen as migrants throughout the southern part of the province. Almost every species of warbler winters in tropical areas from extreme southern United States to Bolivia in South America; the only species that regularly winters in Canada (but not in Saskatchewan) is the yellow-rumped warbler.
Alan R. Smith