Effects of acid rain on bird populations

Abstract

In this paper the effects of anthropogenic acidification of soils and waters on bird populations are reviewed. Acidification causes (i) declines in the reproductive success and the density of piscivorous birds through declines in the fish populations, (ii) shifts in the forest bird community from forest birds to birds of open woodland through large-scale forest dieback, and (iii) leads to a lower reproductive success of birds in calcium-poor areas through a decline in the availability of calcium-rich material (needed for eggshell formation and skeletal growth). Acidification may also affect the availability of food and nest sites for insectivorous and hole-nesting birds, but there are no consistent effects on the population sizes of these birds. Effects of declines in populations of invertebrates in aquatic habitats may be mitigated by reduced competition from fish, and acidification in forests in less-advanced stages of dieback can both lead to an increase and a decrease in insect and seed abundance in forests, the outcome depending on species, extent of leaf and needle loss, and other factors. There is some evidence that acidification may strongly affect avian reproduction through an increased exposure to toxic metals such as aluminium. Anthropogenic acidification on a worldwide scale is expected to continue during the next decades. Future research on the effects of acidification on bird populations should focus on remedial action and effects on population sizes in moderately acidified areas, and should more often apply an experimental approach than in the past.Key words: acid rain, birds, reproduction, calcium, toxic metals, forest dieback.