Cerulean Warblers breed in scattered locations in Eastern North America. They winter along the Andes from Columbia through Bolivia. This species' numbers are cause for concern. Some studies indicate a 50% decline in population during the last 40 years, and numbers have declined even since 1900. Factors that may be contributing to this dire situation include loss of mature deciduous forest, fragmentation of these forests for human development, current early harvesting and shorter rotation of timber stands, loss of inmportant trees to disease (oaks, sycamores, and elms), tropical deforestation in their winter range, and loss of migratory stopover habitat, especially near the Gulf Coast (Hamel 2000).