The most common cause of endangerment is habitat loss. Plants and animals need space to live and energy provided by food, just as humans do.
As human population and consumption increase, wildlife habitat is converted to houses and highways. Forests are cut down for building materials, fuel, and paper. Prairies and forest land are turned into crop land and grazing land for our livestock, and shopping malls stand where wetlands once existed. The damming of rivers to create hydropower has flooded river valleys, making it hard for ocean-going fish to migrate.
Even if habitat is not completely destroyed, it can be fragmented or degraded so much that it can no longer support the species it once did.
Many species, particularly large mammals, need large areas of habitat to survive and reproduce. Patches of forest or grassland surrounded by farms or cities, or divided by roads, will not support these species. (For more discussion of the effects of fragmentation, see Island Biogeography).
A significant percentage of many habitats in North America that are important for wildlife have been destroyed or degraded since the time of European colonization. Over 50 percent of wetlands are gone, 90 percent of ancient forest in the Northwest has been logged, and millions of acres of grasslands have disappeared.
Note: Emphasized words can be found in the glossary.