Birds have been used to monitor the environment throughout history. Aristotle, in 342 BC., described how the behavior of cranes (Grus grus) can be used to forecast the weather, while fishermen from the 17th century through today use flocks of seabirds as reliable indicators of healthy fish concentrations.
Birds are one of the best, and in some cases the only, monitors of environmental change. Serving as natural "biomonitors", conservation biologists and ornithologists have used changes in bird populations and communities, and changes in bird behavior and reproductive ability to (1) examine the long-term affects of habitat fragmentation and introduced species, (2) monitor water quality, (3) indicate the health of marine fishery stocks, and (4) identify environmental pollutants such as organochlorines, heavy metals, and radionuclides.
It is clear why we can use birds important indicators of environmental change:
- Birds are easy to study. Many species are easily identified, detected, and return to traditional breeding sites yearly, so large amounts of data can be reliably gathered from scientists and a concerned public alike. The longest running data gathered on wildlife populations over time comes from Audubon's Christmas Bird Count, providing nearly one hundred years of data on changes in North America's bird populations.
- Birds are well known organisms. Because the biology, ecology, behavior, and evolutionary histories of many birds have been studied extensively, scientists have a foundation on which to ask the most pertinent questions, base hypotheses, obtain answers, and cultivate solutions. This background knowledge reduces risk of misinterpretation, allowing scientists to use birds, sensitive to stresses in predictable ways, as a proxy measure of environmental change. Furthermore, this background knowledge yields cost-effective research, since studies using other groups of animals often requires several years of basic data gathering before monitoring can begin.
- Birds integrate and accumulate environmental stresses over time because they are usually high in the food chain and have relatively long life-spans. Thus birds can be used as indicators of unexpected environmental problems, as when declining numbers and breeding success of birds such as the Bald Eagle (Haliaeetus leucocephalus), Osprey (Pandion haliaetus), and Brown Pelican (Pelecanus occidentalis) revealed that DDT was a pollution hazard.
- Bird populations and communities, and bird behavior and reproductive success often reflect closely the stability of an ecosystem. Thus long-term monitoring programs such as Audubon's Christmas Bird Count, Audubon and the Cornell Lab of Ornithology's joint BirdSource and Project FeederWatch, and the federal Breeding Bird Survey, help reveal declines in population numbers and changes in species' ranges resulting from human-induced causes, providing information crucial to land management decisions.
- Birds hold widespread public interest. Nearly 60 million birders in North America have made birding the second most popular outdoor activity after gardening, spending billions of dollars annually on birding supplies. Volunteer birders participating in citizen science programs form a powerful resource from which to gather data about population trends over a broad geographical range. In North America, such citizen science programs include the National Audubon Society's WatchList, Christmas Bird Count, Birdathon, and Important Bird Areas; Audubon and the Cornell Lab of Ornithology's joint BirdSource and Project FeederWatch, and the federal Breeding Bird Survey.