Wild Neighbors: Hawks and Rodenticides: Another Berkeley Poisoning

By Joe Eaton
Wednesday August 10, 2011 - 02:46:00 PM
Local adult Cooper's hawks with rat. The body of a hawk which died in Berkeley last week contained rat poison, which has frequently been known to kill predators.
Tony Brake
Local adult Cooper's hawks with rat. The body of a hawk which died in Berkeley last week contained rat poison, which has frequently been known to kill predators.
Local juvenile Cooper's hawks with rat.
Tony Brake
Local juvenile Cooper's hawks with rat.

It’s the worst kind of déjà vu. Last month a juvenile Cooper’s hawk was found dead in a pool of blood on a west Berkeley sidewalk, not far from where three other hawks succumbed four years ago. This year’s victim tested positive for the anticoagulant rodenticide brodifacoum, with a trace amount of another rodenticide, diphacinone. Brodifacoum was also implicated in at least two of the 2007 deaths. 

Some rodenticide users, homeowners and professionals alike, seem oblivious to the collateral damage the stuff can cause. Even if the bait is placed indoors, a poisoned rat or mouse can wander outside where it can be picked off or scavenged by a predator or pet. Although Cooper’s hawks are primarily bird-hunters, rats may be “starter” prey for younger individuals, easier to catch than pigeons or starlings. Hard-pressed parents may also bring rodents home for their hungry nestlings. 

Death by brodifacoum is particularly nasty. It kills by internal bleeding, which results in intense thirst. (The 2008 hawks were found in a backyard wading pool.) Like other “second-generation anticoagulants,” brodifacoum was introduced in the 1970s after rodents developed resistance to older products. The risk of secondary poisoning of non-target species like hawks is increased by the fact that the poison is not immediately fatal: a rat may keep coming back to the bait for several days as the brodifacoum in its body builds up to several times the lethal amount. 

According to the American Bird Conservancy , brodifacoum has killed hundreds of birds of prey: red-tailed and Cooper’s hawks, great horned owls, eastern screech-owls, golden eagles. Even mountain lions and endangered kit foxes have fallen victim. In New Zealand, populations of both raptors and insect-eating birds decreased following a brodifacoum-baiting program. 

The second chemical found in the hawks’ tissues, diphacinone, is one of the first-generation anticoagulants. Previous tests on mallard ducks and bobwhite quail had been used to claim that it was only minimally harmful to birds. However, a more recent US Geological Survey study found that small amounts of diphacinone were lethal to American kestrels. As little as 3 grams of liver from a poisoned rodent could kill one of these small falcons. 

A source with the National Animal Poison Control Center says about 160,000 cases of suspected secondary rodenticide poisoning are reported every year. The casualties include pets, livestock, and wildlife. 

Ironically, the new Cooper’s hawk poisoning incident coincided with the US Environmental Protection Agency’s announcement of its final risk mitigation decision on brodifacoum, diphacinone, and eight other rodenticides (, significantly weakened from the agency’s original proposal. Effective in July, the EPA requires that all rodenticides be sold to consumers only with bait stations, as opposed to loose pellets. (Keep in mind, though, that it’s easy enough for a poisoned rodent to exit the bait station and become available to predators or pets. ) And brodifacoum and other second-generation anticoagulants will be sold only to professional pest control operators and through “agricultural, farm, and tractor stores” rather than to the general public. 

The EPA acknowledges that three rodenticide manufacturers—Reckitt Benckiser Inc (D-Con, which contains brodifacoum), Spectrum Group, and Liphatech Inc.---have refused to adopt the new safety measures. The agency says it will take action to remove their products from the market. Pointing out that this could take years, the ABC and ten other environmental groups have called for the immediate removal of the noncompliant products. 

That’s on the national level. Although federal law precludes California cities from banning specific pesticides, the current Municipal Regional Stormwater Permit requires them to establish an integrated pest management policy and ensure that city employees and contractors follow IPM procedures. Berkeley’s pest management policy encourages the preferential use of “reasonably available non-pesticidal alternatives,” including preventive site design and management and physical controls. Although pesticides are considered a last resort, only those “determined to have evidence of causation of cancer, birth defects, mutations, or other severe chronic health effects” are banned from use. The city’s posted policy doesn’t even mention secondary poisoning of wildlife. 

The irony here is that inappropriate use of these products is killing our most effective allies against rodent pests. Hawks and owls are highly competent pest-control agents. Why not let them do their jobs? 

Local wildlife advocate Lisa Owens Viani, founder of Keep Barn Owls in Berkeley, is launching a new group, Raptors are the Solution (RATS), to raise public awareness of the ecosystem services that birds of prey provide and their vulnerability to secondary rodenticide poisoning. "People might say that it's just one dead hawk,” she says. “But one hawk bleeding to death from rat poison is too many. And these are only the birds we know about. Let's not poison the solution to the problem." A planning meeting is scheduled for August 24. If you’d like to get involved, email me: For more background, check out the Hungry Owl Project’s raptors and rodenticides page