Secretariat makes suggestions to prevent future outbreaks
CEC report concludes botulism cause of bird death in Guanajuato

Botulism was the most likely cause of the massive death of waterfowl at the Silva Reservoir in Guanajuato, Mexico, although traces of heavy metals found in sediments and high levels of contamination detected in the reservoir's tributaries may have contributed to the bird kill. This is the conclusion of the International Scientific Panel appointed by the CEC Secretariat to investigate the death of between 20,000 and 40,000 birds in the winter of 1994-1995.

The CEC Secretariat Report on the Death of Migratory Birds at the Silva Reservoir was released last October at the second regular session of the Council of Ministers in Oaxaca and is available to the public.

Among the 21 species of birds affected were ruddy ducks, northern pintails, green-winged teals and white-faced ibises. Three non-governmental environmental groups, the National Aubudon Society, the Grupo de los Cien and the Centro Mexicano de Derecho Ambiental requested that the CEC report on the mass mortality in accordance with Article 13 of the North American Agreement on Environmental Cooperation.

This article allows the Secretariat to prepare a report for the Council on any matter within the scope of the annual program and to obtain the assistance of independent experts in so doing. The Secretariat may also draw upon relevant information submitted by interested non-governmental organizations and persons.

Cause of Death

The Secretariat established a Scientific Panel to assist the Secretariat in preparing the report. The panel included experts in biology, hydrology and other pertinent areas. After several meetings, on-site investigation and sample studies, the Scientific Panel evaluated the available hypotheses (chromium poisoning, botulism, and insecticide poisoning), concluding that: "botulism was the overwhelming cause of death of the waterfowl at the Silva Reservoir. Nevertheless, a small percentage of the birds may have died due to other causes." The Panel based its conclusion on the following evidence: descriptions and videos showing waterfowl affected by the typical symptoms of botulism; a report from nacec.the Fundación Ecológica de Guanajuato [Guanajuato Ecological Foundation]; the recovery of some waterfowl; the presence of the botulinum type C toxin in the tissue of waterfowl taken for examination; the presence of clostridium botulinum spores, capable of producing the toxin; and the fact that "the conditions in the Silva Reservoir favored outbreaks of botulism".

Birds that may have died from nacec.other causes, such as exposure to heavy metals, may also have triggered a subsequent larger die-off from nacec.an outbreak of botulism. Traces of heavy metals, especially chromium, which are heavily used by industry in the area, were found in carcasses as well as in sediment samples; higher concentrations were especially prominent in the more superficial sediment, and "in some cases these exceeded the levels recommended by the U.S. Ministry of the Environment for non- contaminated sediment". The researchers found that the Silva Reservoir pollution problem extends to its tributaries: "the information obtained by the group clearly shows that the River Turbio and its main tributaries constitute a highly contaminated and overloaded ecosystem".

The Scientific Panel recognized in its findings the important efforts made by Mexican government agencies, scientific institutes and social organizations to identify and evaluate the cause of the waterfowl mortality. It also recognized the government’s effort to address pollution in the Silva Reservoir and to revise and step up the clean-up plan of the Turbio River, known as the Turbio River Initiative. The full implementation of this initiative was identified as being key to the restoration of the Silva Reservoir.

To this end the Secretariat submitted a list of suggestions for the Council’s consideration. These included a number of actions for recommendation by Council to the Mexican government, namely: a comprehensive clean-up program for the region; the establishment of an independent mechanism, broadly representative of all interested stakeholders, for monitoring and reporting on the progress and result of the initiative; conducting a comprehensive evaluation of the environmental compliance situation in the area; and; the design and implementation of a targeted pollution-prevention program so as to substantially decrease industrial pollution.

In its report, the Secretariat also recognized that the deaths of waterbirds on a massive scale occur with relative frequency in North America. The National Wildlife Health Center, based in the U.S., has recorded at least 25 die-offs in Canada and the U.S. since 1970, each involving from nacec.20,000 to 100,000 waterbirds. The causes of these deaths varied and have included botulism, avian cholera, oil spills and pesticide contamination.

The Secretariat also suggested to the Council the importance for Mexico to develop a national wildlife health surveillance for the investigation of, and response to, wildlife disease outbreaks. It also suggested that the Mexican surveillance program be linked to existing programs in Canada and the U.S., to form a trinational response network to address wildlife mass mortalities. The Secretariat further suggested to Council the need to strengthen cooperative efforts to support Mexico in obtaining the financial means to be able to carry-out the implementation of the Rio Turbio clean-up.

An Opportunity for Action

The CEC Secretariat emphasized the opportunity for international cooperation afforded by the Silva Reservoir incident. The event "serves as a reminder of the various biological links shared by the three nations and strengthens the common responsibility to work in a joint manner in order to preserve and protect these valuable international resources." The Silva Reservoir incident can become an important catalyst for greater cooperation between Mexico, the United States, and Canada, particularly in responding to and preventing mass wildlife mortalities.

The Council is currently reviewing the Secretariat Report and preparing a response.