Birds Specialize in Where They Nest
It takes a landscape scattered with an entire range of successional stages of vegetation to support a full complement of bird species. In hot, dry portions of the Ponderosa Pine and Interior Douglas-fir biogeoclimatic zones in southeastern British Columbia, most of the 25 bird species studied nested in either grass, shrubs or trees, or a combination of these features, associated with discrete seral stages.
These easily-recognizable vegetation features are enough to identify breeding habitat for specific birds. For instance, grass indicates habitat for birds that nest at early-successional sites, such as mountain bluebird and western meadowlark. Certain birds, such as western tanager, associate with conifers 1 to 10 metres high, while others, like red-breasted nuthatches, nest in forests at a later successional stage, with trees over 10 metres tall. Other species, including dark-eyed junco and mountain chickadee, are more generalists and associate with all heights of conifers.
Whether the vegetation comprises shrubs mixed with grass or shrubs mixed with young trees also influences which birds nest there. Lewis' woodpecker and cedar waxwing, among other species, use the grass-shrub mix of vegetation, while blue grouse, Townsend's solitaire and blue-headed vireo choose sites growing shrubs and young conifers.
Francis E. Schwab, Neal P.P. Simon and Anthony R.E. Sinclair. 2006. Bird-Vegetation Relationships in Southeastern British Columbia. Journal of Wildlife Management. 70(1): 189-197.