A report by a team of conservation biologists concludes that the total number of birds in North America has dropped precipitously since 1970. Annual surveys monitoring the biodiversity and abundance of bird populations across the North American continent indicate that almost 30% of all North American birds have disappeared over the past 50 years. These declines translate into approximately 3 billion individual birds being lost, which many scientists regard as an ecological crisis. The net losses appear in almost all bird groups, including common as well as rare birds, and both native and invasive species. In particular, sparrows, larks, finches, starlings, and blackbirds have been affected, with losses totaling more than 50% in many cases. The loss of bird abundance is also evident in most avian habitats, including grasslands, forests, deserts, and coast and shore areas. If this trend continues, scientists fear that the disappearance of vast numbers of birds could lead to the collapse of numerous ecosystems, especially given that birds play key roles in pollination, seed dispersal, and insect and pest control. See also: Aves; Biodiversity; Desert; Ecology; Ecosystem; Forest; Forest ecosystem; Grassland ecosystem; North America; Pollination; Population ecology
The biologists analyzed population-level data dating back to 1970 for 529 bird species in North America, which represents 76% of all North American birds. The observed plummeting of bird populations since that year is remarkable, and most scientists believe that the causes of the sharp declines in bird abundance are anthropogenic; that is, the declines in bird abundance result from the influence of human beings on nature. Specifically, habitat loss and degradation, urbanization, various forms of pollution, the use of pesticides, and agricultural expansion have collectively created scenarios in which many birds are unable to adapt and, thus, unable to survive. The loss of nesting areas for many migratory species as a result of urban development has been particularly detrimental to bird populations. See also: Adaptation (biology); Agriculture; Air pollution; Anthropocene extinction; Migratory behavior; Pesticide; Population viability; Water pollution
However, one type of habitat is not experiencing the aforementioned losses in bird abundance. Wetlands constitute the lone exception, and the numbers of wetland birds (especially waterfowl, such as ducks and geese) have increased. This is because wetland habitats have been legally protected for many decades and have been restored, or are undergoing restoration, through numerous conservation efforts. In addition to wetland birds, a few other individual bird species have seen gains in abundance. For example, the abundance of bald eagles, falcons, and ospreys has risen since the 1970s. Conservation efforts—especially the banning of the insecticide dichlorodiphenyltrichloroethane (DDT) in 1972—are responsible for the uptick in raptor populations. Because of successful conservation steps taken with regard to raptors and wetland birds, scientists believe that similarly strong preservation measures undertaken for other bird species in a variety of remaining habitats would undoubtedly lead to increases in the abundance of these birds. The population crisis requires prompt action, though, especially as numerous habitats are presently undergoing irreversible alterations as a result of global climate change, further complicating the viability of many bird species. See also: Conservation of resources; Conservation of species; Environmental management; Global climate change; Insecticide; Restoration ecology; Species and global climate change; Wetland
