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Scientists from Canada and the US have
observed declining populations of Swainson's hawk for several years, but they
knew little about their migratory habits until 1994. During 1994/95,
ornithologists from the US Forest Service started investigating this migration
because the hawks were not returning to North America in their usual numbers.
The following season detailed research using miniature satellite transmitters
led to the discovery of 4,000 dead Swainson's hawks in the La Pampa region
west of Buenos Aires. Investigators estimated that a total of 20,000 hawks
probably died over an area of approximately 200 km by 250 km. Over 700 dead
hawks were found in one roost alone.
The ornithologists suggested exposure
to monocrotophos, used in the region to control grasshopper pests, was killing
the hawks. They thought it caused poisoning either by direct exposure to the
spray, or through secondary poisoning when the birds ate contaminated
grasshoppers. The favourite roosting grounds of these birds are in the alfalfa
growing areas of the La Pampa region. An unusual combination of a grasshopper
plague on this crop, misuse of the product and a large number of one bird
species in one location contributed to the problem. Technically the authorities
did not recommend monocrotophos use for grasshopper control, although in
practice they had done very little to stop it.
Chemical residue analysis of the carcasses carried out by
Novartis Crop Protection (the world's largest pesticide company formed
recently by a merger between Ciba Geigy and Sandoz) and the US Institute of
Wildlife and Environmental Toxicology at Clemson University confirmed that
monocrotophos was responsible for the mass hawk-kill.
Other insecticides used in the region to control grasshoppers
include the OPs dimethoate, chlorpyrifos, fenitrothion and methamidophos, and
the synthetic pyrethroid cypermethrin.
Swainson's hawk and other birds are very sensitive to low levels of some OPs,
including monocrotophos. For example, the oral LD50 for bobwhite quails is 0.94
mg/kg and is 2.8 mg/kg for house sparrows. The American Bird Conservancy (ABC) a
Washington - based advocacy group representing 56 environmental and
ornithological organisations, says that major bird kills involving monocrotophos
have been reported over the last 25 years. The World Health Organisation
classifies the formulation as 'highly hazardous' (WHO Class Ib).
As a result of the hawk deaths, a joint
meeting with the ABC, the Canadian Wildlife Service and Novartis was held in
August 1996. During the meeting, a set of detailed written agreements were
produced. The main outcome was a decision not to use monocrotophos in the La
Pampa region and to replace it with less toxic chemicals, particularly to avian
species, such as the cypermethrin. However on the ground the OPs dimethoate and
chlorpyrifos are being used in conjunction with cypermethrin which is still less
toxic than using monocrotophos on its own. Gerald Winegrad of ABC says farmers
in the region should adopt more integrated pest management techniques.
Novartis, the market leader for
monocrotophos, encouraged other local distributors to stop selling
monocrotophos. A campaign to inform local farmers of the restriction was set up
through the local media. Posters (see photo) were also distributed.
ABC, its Argentinian equivalent AOP, the
US Fish and Wildlife Service, the Argentinian government and Novartis have been
running training sessions to help field workers identify affected birds and
carry out toxicological analysis for OP and carbamate insecticides.
Ornithologists
did field studies in January 1997 which established that the restrictions had so
far been successful. All the data is not yet in and the full picture will not
emerge until the end of March. So far there has been one report of 26
Swainson's hawks killed on the fringe of the problem area.
Conclusion
It is rare that
industry and conservationists come together in such a way. Jacob Brassel of
Novartis said: "It was encouraging that everybody collaborated because it
meant measures to control the problem could be quickly put into place and acted
upon."
Gerald Winegrad
of ABC said: "The goal was to convince the company to take monocrotophos off
the market world-wide because of its acute toxicity, especially to many bird
species. However, in this case Novartis has been very helpful in trying to
reduce Swainson's hawk deaths." (DB)
[This
article first appeared in Pesticides News No. 35,
March 1997, page 6]