A new study by scientists from Maryland and Colorado using American kestrels(美洲隼) , a surrogate(代理的) test species for raptorial birds, suggests that they are at greater risk from poisoning from the rodenticide(灭鼠剂) diphacinone than previous believed. The research, published in Environmental Toxicology and Chemistry, considers the threat posed by diphacinone as its usage increases following restrictions3 on the use of similar pesticides5. "Recent restrictions on the use of some rodenticides may result in increased use of diphacinone," said lead author Dr. Barnett Rattner from the US Geological Survey. "Very few controlled studies have examined its toxicity6 in birds so it is important to determine how lethal7 this chemical is to wildlife."
Surveillance programs have reported detection of rates of rodenticide in birds of prey8 across France, Great Britain and Western Canada, revealing that several second-generation rodenticides can result in non-target deaths, with possible population-level implications.
However, the global magnitude of non-target poisoning through the routine use of rodenticide, or through targeted eradication9 programs remains10 unknown, partly because the indirect fatalities11 go largely unnoticed and unreported.
The team tested kestrels and discovered the effects of diphacinone and the quantity required for a lethal dose. The results showed that birds that had ingested greater than 300 mg per kilogram of body weight died within 8 to 23 hours, while those ingesting a dose of 118.6 mg/kg survived 27 to 47 hours. At lower doses, nearly all of the birds survived.
Poisoned birds displayed some evidence of internal bleeding, although histological(组织学的) examination of internal organs revealed hemorrhaging(出血) over a wide range of doses. The results demonstrate that doses that reach or exceed 79 mg/kg body weight are lethal for kestrels.
"Our study, combined with previous research in hawk12 and owl13 species show that birds of prey are considerably14 more sensitive to diphacinone compared to species such as bobwhite(美洲鹑) quails15 and mallards," said Rattner. "Their protection requires more substantial safety margins16 than are afforded to species of game birds traditionally used in pesticide4 registration17 studies."
Using their results the team estimated how much poisoned prey a hawk or owl would need to consume before ingesting a lethal dose. Using a probabilistic(概率的) risk approach, the team estimated that an endangered hawk or owl would be at risk if it consumed as little as 3 to 4 grams of liver from a poisoned rodent1.
"Diphacinone was found to be considerably more toxic2 to American kestrels than previously18 reported in tests of other wildlife test species", concluded Rattner. "These data, in combination with similar measurements in Northern bobwhites, will assist in the development of a pharmacodynamic(药效的) model and a more complete risk assessment19 of diphacinone for birds."