Acid Rain & Bird Eggs
Acid rain indirectly causes damage to bird eggs by depleting breeding birds of calcium in their diets, causing eggshells to be thin and easily breakable.
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Sources of Acid Rain
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Acid rain has increased since the dawn of the Industrial Revolution. Humans generally produce acid rain through emissions from factories that release combinations of sulfur, nitrogen and carbon into the air and mix with naturally occurring water molecules. Volcanic eruptions also cause acid rain to form.
Food Chain
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Declines in snail populations herald drops in nesting success for some bird species. Acid rain depletes calcium in soil. Snails that typically feed on that calcium as they excrete their shells die off in areas of acidic soils. Birds that rely on the snails as food can survive by eating other prey, but are unable to produce sturdy eggs.
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Wood Thrushes
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Wood thrushes can survive by eating spiders and other organisms, but without snail shells in their diets, they lack the calcium needed to produce structurally sound eggs and healthy hatchlings. The Cornell Lab of Ornithology's Birds in Forested Landscapes citizen science project proved that wood thrush populations declined in places where acid rain typically falls in the eastern United States.
Songbirds in Slump
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The number of small songbirds in Europe known as great tits have declined in areas with acidic soils. The Institute for Forestry and Nature Research in Holland corroborated the Cornell study's findings, proving that a species of songbird, the great tit, declined in areas where snails had disappeared.
Experiments
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Artificially placed chicken egg shell fragments provided enough calcium to raise wood thrush nesting success rates in acid rain-affected areas. Cornell found that spreading chicken egg shells in a calcium-depleted area leads to greater nesting success among wood thrushes. The Institute for Forestry and Nature Research achieved similar results with great tits by spreading lime.
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References
Resources
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