Birdwatch News Archive

It seems all pesticides have some kind of ecological 'knock-on' effect, as American Kestrels are now finding out. Photo: Steve Hillebrand (commons.wikimedia.org)

American raptor poison fears

Posted on: 14 Mar 2011

An unrestricted new pesticide has been shown to kill birds of prey in America, reviving bad memories of the DDT crisis in the 1960s.

New research on American Kestrels has shown that the rodenticide diphacinone - widely used as a substitute for rodenticides now banned or restricted by state law - shows significant build-up in the birds of prey at the top of the food chain, resulting in rapid fatalities.

American Kestrels that ingested more than 300 mg per kg of body weight died within 23 hours; others consuming a dose of 118 mg per kg also died, lasting no more than 47 hours. Lower doses resulted in survival. It is not known if the rodenticide affects breeding success like DDT, but any dose greater than 79 mg/kg appears to be eventually lethal for the small raptors.

The poison is developed to be tasteless and have a delayed action, which means that the live-prey eating kestrels are highly likely to eat contaminated mice and rats, as they will still be active after eating poisoned bait. Diphacinone is an anticoagulant which causes profuse unstoppable bleeding. Recovered kestrel corpses showed evidence of internal bleeding, though haemorrhaging was present even at non-lethal doses.

Using American Kestrel as surrogates for less common raptors, the study showed that protection limits for birds of prey need to be lower than the gamebirds previously used a surrogates. Rodenticides have also been found to be present in French, British and Canadian birds of prey, with possibly derogatory effects on populations exposed to the chemicals.

Reference: Rattner, B, Horak, K, Warner, S, Day, D, Meteyer, C, Volker, S, Eisemann, J, and Johnston, J. 2011. Acute Toxicity, Histopathology, and Coagulopathy in American Kestrels (Falco sparverius) Following Administration of the Rodenticide Diphacinone. Environmental Toxicology and Chemistry DOI:10.1002/etc.490