Loon Magic/Loon Magic - Wayzata Technology (8011) (1993).iso/mac/mac text/13 Hanging On - Chemical...

Text File | 1993-07-20 | 8KB | 135 lines

   HANGING ON

"The plight of the loon takes many forms, often human-induced:
artificial water level fluctuations that flood or strand vulnerable
nests; predation; loss of nesting habitat to development; disturbance
during the nesting season. The most insidious threat of all is acid
rain, which has already killed hundreds of lakes, and will destroy all
life in many more unless its sources are controlled." -Jeff Fair, 1983

   It's a tough world for loons. They have battled diseases,
competition from other species, high and low water levels, predation
and other natural threats for millions of years - and survived them
all. During the past few decades, however, Homo sapiens hasn't made
the loon's lot any easier. While the sport shooting of loons is
thankfully a sad memory, a frightening list of new and more
insidious problems is facing the bird: toxic chemicals, acid rain,
destruction of nesting habitat, nest flooding, increased predation
caused by the exploding populations of some predators, commercial
fishing operations which net loons in addition to fish, and harassment
by people. None of these problems faced loons when Native
Americans developed their versions of loon religion. Some are
serious enough to threaten the very existence of the species; others
are just nagging problems in restricted geographic locales. But all
must be dealt with if the cry of the loon is to be heard in the twenty-
first century and beyond.

   Chemical Contamination

   The story of chemicals and birds has always been disturbing. While
most of the more than 60,000 man-made chemicals in our
environment do not cause problems, at least a few are potentially
dangerous. The role of dichlorochdiphenyl-trichlorethane (DDT) in
the population declines of the eagle, osprey and peregrine falcon is
well documented. At high levels, DDT prevents the eggshells of these
and other birds from reaching normal thickness, and when a nesting
bird sits on its thin-shelled eggs, the eggs are crushed. Synthesized in
1874 but used widely only during and after World War II, DDT was
called a modern miracle.

    For a time it controlled mosquitoes and other pests, but the
miracle was short-lived. Pests developed resistance, even immunity,
to the toxin. By the 1960s, a few people saw the tip of the DDT
iceberg. In 1962, Rachel Carson's Silent Spring alerted the public to
the dangers of indiscriminate DDT use and indirectly launched the
environmental movement. By the mid 60s, the spectacular peregrine
falcon had disappeared from much of its range, a victim of DDT. The
osprey, once a familiar East coast raptor, declined rapidly, as did the
bald eagle. In 1972, the Environmental Protection Agency banned
DDT in the United States, but DDT is still being used in other parts of
the world. While the worldwide situation is improving, many birds
now pick up DDT in their wintering habitats. Of the 650 species of
birds breeding in the United States, 332 species spend the winter in
tropical areas of Mexico, the West Indies, Central and South
America - all areas where DDT is still used.In the northern half of the
Midwest, decreases in the eggshell thickness of many birds, including
eagles, have been documented. Studies by University of Wisconsin
researchers Joseph Hickey and Raymond Faber indicated eggshell
thickness decreases in nine of thirteen fish-eating species when
shells from 1970 were compared with museum samples collected
before 1946. In great blue herons, the eggshell thickness decrease
was twenty-five percent. Black terns, double-crested cormorants,
herring gulls and red-breasted mergansers had shell thickness
decreases of thirteen to twenty-three percent.

   Fortunately, loons have not as yet been as seriously affected. In a
Wilson Bulletin article, Scott Sutcliffe reported an eleven percent
decrease in loon eggshell thickness when comparing 1978 eggs from
Squam Lake and Lake Winnipesaukee in New Hampshire with
museum samples. The level of DDT present correlated with the
thickness of the shellmthe higher the level of DDT, the thinner the
shell - but the differences were slight. The average thickness of the
fourteen 1978 eggs was 0.59 mm while the museum samples, all
dating to a pre-DDT era, had an average thickness of 0.65 mm.
According to Sutcliffe, the eggshell thinning problem had little or no
effect on loon productivity in New Hampshire.

   Canadian research has also demonstrated the presence of chemicals
in loons. Eggs collected in 1970 were significantly thinner than
thirty-nine eggs from The Royal Ontario Museum which were
collected before 1947. More importantly perhaps, the more recent
loon eggs contained traces of DDT, Mirex, PCB, dieldrin and mercury.
Mercury levels in eggs from the Algonquin Park area were quite
high, 1.11 parts per million (ppm) in one case.

   Contaminants were found in loons too. As reported in the Journal of
Environmental Contamination and Toxicology, one group of
investigators analyzed 204 loon carcasses found between 1969 and
1979. Except for a few that were shot or died from swallowed
fishhooks, these loons drowned in commercial fishing nets. Of the
204 loons, thirty were found in an emaciated condition. Of these
thirty, seven loons had lethal levels of mercury and one a very high
level of lead. All of the loons had evidence of at least some DDT, PCB,
dieldrin and mercury contamination, but the levels in the emaciated
loons were significantly higher than in the 174 non-emaciated loons.
The levels of mercury in the livers of healthy, juvenile loons, for
example, averaged 1.92 ppm while the average in emaciated
juveniles was 26.4 ppm. For adults, the equivalent numbers were
6.35 ppm in healthy loons and 16.3 ppm in emaciated birds.

   Jack Barr, a well-known Canadian loon researcher, has documented
mercury problems for loons in northwestern Ontario. Studying loons
on lakes on the Wabigoon-English River system, Barr found mercury
contamination in fish and loons and noted reductions in egg-laying,
and in nest and territorial fidelity. The source of mercury in many
lakes was the chloralkali plant at Dryden. Loons farther downstream
from the plant had less mercury and were able to reproduce better
than loons occupying lakes closer to the Dryden plant.

   Barr also noted that some lakes had naturally occurring mercury
associated with greenstone deposits. Acidification of these lakes will
probably elevate mercury levels and cause further problems for
loons and other aquatic birds.

   Loon feeding habits may offer some protection from DDT and other
toxic chemicals. Because toxic chemicals can work their way up
through the food chain by a process of bio-accumulation, chemicals in
lake water may be present at a relatively harmless level of parts per
trillion, but when microscopic zooplankton absorb the chemicals, the
contaminants can be concentrated to parts per billion. And when
small minnows and fish eat the zooplankton, the concentrations can
reach parts per million. When predator fish eat small prey, they
store this cumulative contamination in their fat tissues; so, an eagle
feeding on the carcass of a large fish can get a heavy dose of
chemicals. Since loons usually feed in a safer area of the food chain,
they do not pick up nearly the contamination absorbed by eagles or
ospreys feeding on large prey.

   Wildlife managers are showing concern but not panic over the
growing body of scientific evidence documenting the presence of
chemical contaminants in loons. While the jury is still out, scientists
do know that loons are carrying fairly high levels of PCB and
mercury. The fact that loons continue to reproduce despite their
body burden of chemicals and metals is no cause for joy; it might just
buy them a little more time.