Human disturbance and pollution are to blame
for their disappearance
Thousands of herons, egrets and ibises once raised their young on
the islands of the Arthur Kill and Kill van Kull. Today, those
islands are empty, and no one can say why.
Those who have tracked the birds since 1985 say human disturbance
and pollution are the prime suspects.
Some of the herons have moved to other islands in the harbor, but
many more are missing. In 1995, about 2,000 pairs built their nests
in New York Harbor. Last year, that number dropped to 1,500 pairs.
Researchers called an emergency meeting last month at the College of
Staten Island to discuss the herons' fate. The event drew dozens of
city officials, scientists and birders from near and far.
The birds were first discovered here in 1974. Dr. Katharine Parsons
of the Manomet Observatory in Manomet, Mass., began studying them
for the New York City Audubon Society in 1985. Dr. Paul Kerlinger,
an environmental consultant, took over the annual surveys for
Audubon in 1995.
The birds' disappearance has caught many by surprise. The heron
colonies seemed strong -- even after oil spills in 1990 dumped more
than a million gallons of petroleum products into local waters.
Bird populations normally go up and down from year to year, said Dr.
Kerlinger, and herons are known to move around.
"I just kind of shrugged these things off because herons regularly
abandon islands and recolonize them," he said.
But when the declines continued, he asked Audubon to call the
meeting.
Dr. Parsons has studied heron colonies in much of the northeast
United States, and has seen their numbers drop throughout the
region.
"My message today is that herons are not only in decline in urban
estuaries, as they are here, but are also in decline in many places
on the East Coast," she told those gathered at the meeting. From
Delaware to Massachusetts, heron populations have dropped 25 percent
since the 1970s, she said.
When she compared the New York birds to those in other parts of the
northeast, she found that the urban birds were actually doing better
than those in rural areas.
The rural birds are declining faster due to their exposure to
chemicals in use in agricultural areas, said Dr. Parsons. She has
found evidence of these chemicals -- organophosphates and carbonates
used as pesticides -- in the birds' regurgitated food and on their
feet.
The urban birds are also being exposed to pesticides and other
chemicals once manufactured here. Dr. Parsons found higher levels of
DDE (dichlorodiphenyldichloroethylene) in heron eggs here than
anywhere else she studied. DDE is a by-product of DDT
(dichlorodiphenyltrichloroethane), a pesticide banned in the U.S. in
1972 because it was found to injure wildlife. The urban birds have
been exposed to PCBs (polychlorinated biphenyls), which are known to
cause cancer and other health problems in animals.
Dr. Parsons believes that the herons are actually doing worse in New
York harbor than it seems. She thinks that the herons in rural areas
have been migrating to the city -- just as some humans do -- for a
better life. But they are not thriving here either.
"Unfortunately, it's not good news," Dr. Parsons said. "It doesn't
look like the heron colony is sustainable with the wetlands
resources we have in New York harbor."
Researchers are gearing up for another survey, and they hope to see
the birds returning to the islands off Staten Island's west shore.
"When an area's abandoned, what is the chance that it will be
recolonized?" one participant asked at the meeting. "There must be
some data on that -- some hopeful data, I think."
No one could answer him.
