Pollution, of many diverse types, has direct and indirect impacts on birds—an indication of the wider problems it creates for humans and biodiversity alike. Water-borne pollutants can devastate otherwise productive wetland and coastal habitats. Many pesticides linked to bird deaths are still in widespread use, especially in developing countries. Oil spills remain a threat to some seabirds, while solid waste is an increasing problem. Little is known of the long-term effects of many pollutants, including those that persist and accumulate in the environment.
Pollution from a wide range of sources affects birds: agricultural and industrial effluents and urban wastewater can all have serious direct impacts on bird populations, through increased mortality, as well as less immediately obvious through reducing fertility (). Pollution can also have strong indirect effects on birds, by degrading habitats or reducing food supplies. More generally, birds can serve as invaluable indicators of the wider impacts of pollutants. They are often the most visible sign of the environmental problems caused by oil slicks () and have highlighted the broad environmental impacts of less well known persistent organic pollutants () and of acid-rain ().
Huge areas of farmland, rangeland, forest and wetland are treated with poisonous synthetic chemicals each year to control various plants, animals and disease-causing micro-organisms. Agriculture in the developing world in particular is becoming increasingly reliant on such biocides, many of which have been banned or restricted elsewhere. Unfortunately, their side-effects and longer-term impacts are often ignored or simply not known by those who use them and they have been identified as a contributory factor to the threatened status of many bird species (). Recently, a veterinary drug used to treat livestock has been linked to the collapse of vulture populations throughout South Asia ().
Rubbish and solid waste are also known to have serious impacts on many ecosystems and populations of wild species. For example, ‘junk’ dumped in the terrestrial environment is swallowed by scavenging raptors, resulting in low breeding success (). Such junk includes toxic lead shot, which is also a particular problem for waterfowl and gamebirds (). Likewise, floating plastic garbage dumped in the marine environment is commonly mistaken for prey by albatrosses and petrels, causing starvation and death ().