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The straight guano on thinning bird egg shells, almost.

 (From Science News On-Line)

 April 25, 1998

Birds' eggs started to thin long before DDT

by S. Milius

By combing museum collections for old birds' eggs, a researcher has
found that thrush eggshells in Great Britain were thinning by the turn
of the century, 47 years before DDT hit the market.

The pesticide, now banned in most countries, caused such dramatic shell
thinning that populations of peregrines, ospreys, and other top
predators began to decline.

Long before DDT was a glimmer in a farmer's eye, some other menace, as
yet unknown, was sapping the strength of eggshells, claims Rhys E. Green
of the Edinburgh office of the Royal Society for the Protection of
Birds. In the April 22 Proceedings of the Royal Society of London B, he
describes long, slow shell declines.

Eggshell thinning may have been an early consequence of
industrialization, Green speculates. Acids formed when pollutants belch
out of coal furnaces and smokestacks may have changed soil and water
chemistry enough to reduce the availability of calcium, which is
critical for eggshells. "Calcium can be a particularly bad pinch point,"
Green says.

Other research has linked acidified soil to frail eggs, he notes. J.
Graveland of the Netherlands Institute of Ecology at Heteren reported in
1994, for example, that great tits lay weaker eggs as calcium-rich
snails dwindle on acidified soils.

In an unusually broad survey, Green measured three museums' collections
of well-labeled eggshells gathered since 1850 from four thrush species
in Great Britain. Eliminating bad eggs still left Green several thousand
to measure. "You get quite quick," he says.

From the weight and dimensions of the shells, he calculated an index of
thickness similar to those developed for monitoring DDT effects. For two
species, he also measured shell thickness by fitting a thin probe
through the hole made to remove the material inside the egg in
preparation for museum storage.

Both the index and the direct measurements show steady declines.
Blackbirds (not the U.S. blackbird but Turdus merula, a cousin of the
U.S. robin) have lost 7 to 10 percent on the shell index since 1850.
Eggs from song thrushes thinned 6 percent, mistle thrushes 4 percent,
and ring ouzels 2 percent. Only the ring ouzel leaves Great Britain for
long migrations.

The research did not look for effects of weakened shells on bird
populations, but Green points out that other species have withstood
eggshell declines of up to 15 percent.

"I think he probably has something," says wildlife toxicologist D.
Michael Fry, director of the Center for Avian Biology at the University
of California, Davis. "There is a lot of scatter, but the trend is

Acidification as a threat to eggshells sounds plausible to Lloyd Kiff,
now science director at the Peregrine Fund in Boise, Idaho. More than 2
dozen recent studies show acid effects on songbirds abroad, but no
research has been done in the United States, he says. "I don't know why
someone hasn't picked it up and run with it," he adds. "We have similar
conditions here."

From Science News, Vol. 153, No. 17, April 25, 1998, p. 261.
Copyright Ó 1998 by Science Service.


Graveland, J., et al. 1994. Poor reproduction in forest passerines from
decline of snail abundance on acidified soils. Nature 368(March 31):446.

Green, R.E. 1998. Long-term decline in the thickness of eggshells of
thrushes, Turdus spp., in Britain. Proceedings of the Royal Society B.
263(April 22):679.


D. Michael Fry
University of California, Davis
Center for Avian Biology
Davis, CA 95616

Rhys E. Green
Royal Society for the Protection of Birds
17 Regent Terrace
Edinburgh EH7 5BN
United Kingdom

copyright 1998 ScienceService

I found this on the internet and copied it from the Science News
Homepage. I read this almost two years ago and my memory failed me when
I said bird egg shells in Europe have been thinning for the past 300
years. It's only been documented that they have been thinning for the
past 150 years. I get the print copy of Science News and it sometimes
differs somewhat from the online versions.

Dan Nelson
Bridgeville DE
zone 7

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