The Canadian Peregrine
ARTICLE 6 - Argentine
Spray Kills Hawks From Canada
Pesticides sprayed on fields in Argentina are killing tens
of thousands of wintering Swainson's hawks that nest on the Canadian Prairies
and the adjacent U.S. Great Plains.
(by Peter Whelan)
A researcher from the U.S. Forest Service counted 3,909 dead hawks in a
50-kilometer square last week and estimated they represented between 20,000 and
40,000 dead. The count was incomplete, partly because scavenging vultures and
caracaras were eating the bodies quickly.
The insecticide monocrotophos and other pesticides are being sprayed from
aircraft and tractors to control grasshoppers in fields of alfalfa and other new
crops. Hawks flying behind the tractors to seize flushed grasshoppers get
sprayed directly, then eat more pesticide in the grasshoppers.
Scientists from Canadian and U.S. governments and universities are working with
the Argentine environmental agency, INTA, to propose a change to less severe
Research scientist Geoff Holroyd of the Canadian Wildlife Service in Edmonton
said the situation needs urgent action, especially since the Swainson's hawks
have been in decline for a decade in their main Canadian breeding grounds in
Saskatchewan and Alberta. Nesting failures have explained part of the problem,
but researchers have been puzzled and alarmed by a further downward drift.
"I think this is comparable to what happened to the peregrine falcon inthe
1950s and 1960s. Hopefully, we have caught it in time," Mr. Holroyd said.
"This went to the Environment Minister's desk, and he approved action
within 24 hours."
The anatum race of peregrines was all but wiped out by pesticides in eastern
North America three decades ago and is just coming back now with the help of
planting programs. Mr. Holroyd is chairman of the Canadian committee working to
rebuild the peregrine population.
Environment Canada is funding field work by INTA, and Canadian farm experts are
to offer advice about pesticides. "It is too late to do anything this year,
but we hope for a solution by next winter," Mr. Holroyd said.
The Swainson's hawks will leave Argentina at the end of February and spend two
months migrating north.
The big, dark-chested hawk is a familiar sight soaring over the Canadian
Prairies on uptilted wings, like a vulture. It raises its young largely on
Richardson's ground squirrels but eats many insects after migrating in large
flocks to the wintering grounds on the South American pampas.
The Canadian population is estimated at 40,000 to 100,000 in a world population
of 350,000 to 400,000. Canadian birds were inordinately represented in the
Argentine deaths. Of 12 leg bands recovered, nine were from Alberta and
Saskatchewan hawks. Two Alberta hawks tagged with satellite transmitters are
both in the danger area.
The study area is at the junction of the states of Cordoba, Buenos Aires and La
Pampa. Cattle ranching used to dominate, but irrigation recently opened the area
to a variety of crops. This is only a small part of the winter range of the
hawks and a small part of the cultivated farmland. "We don't know how far
this problem extends," Mr. Holroyd said. Ninety per cent of the killed
hawks were adults. The separate winter range of immature birds is not known.
Monocrotophos is an organic phosphate insecticide that is fast-acting and highly
toxic to birds and animals. It kills insects either on contact or when taken in
with crops. It is no longer sold in the United States and was never registered
At worst, the Argentine toll would represent 5 per cent of the world population
and half the Canadian population, Mr Holroyd said. "This appears to
explain the decline in this hawk. We also speculate that secondary effects of
the pesticides could be reducing nesting success of the birds when they return
Concern that Argentine pesticides were hurting migrant North American hawks
appeared in birding literature as long ago as 1968, but there were no specifics.
The first solid evidence came last year when 700 Swainson's hawks were found
dead in the same area, apparently from pesticide poisoning.
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