For many species the largest contributing factor is the loss of habitat both in wintering and nesting grounds. These two types of ecosystems are used by a large number of species to raise their young. In Central and South America habitat is loss due to clear cutting for agriculture. These factors cause species to crowd into smaller and smaller area and increase competition for resources. While natural areas are set aside for wildlife in both nations, this habitat loss also leads to an increase in habitat fragmentation.
Habitat fragmentation is the reduction in the size and dimension of a system into smaller units.
Habitat fragmentation often reduces the amount of resources available for a species. It may limit the size of territories, decrease availability of nesting sites or reduce food resources. Habitat fragmentation can be seen more in the United States as areas are set aside as wildlife islands surrounded by cities and towns. Large areas are diced up into smaller pieces with roads bisecting them. In the case of forest fragmentation of the deep woods needed for many warblers is limited.