Birds that migrate each year between the American tropics and higher latitudes, especially in North America, are known as neotropical migrants. So called because they migrate from the tropics of the "new world" (the Western hemisphere), neotropical migrants are a topic of concern because many species have been declining in recent years, and because they are vulnerable to habitat destruction and other hazards in both winter and summer ranges. One survey of 62 forest-dwelling migrant bird species found that 44 declined significantly from 1978–1987. Migrants' dependence on nesting and feeding habitat in multiple regions, usually in different countries, makes conservation difficult, since habitat protection often requires cooperation between multiple countries. In addition, it is often unclear whose fault it is when populations fall. Most of the outcry over neotropical migrants has been raised in the United States and Canada, where summer bird populations have thinned noticeably in recent decades...