WildCare Test Results Show Barn Owl Died of Rat Poison

WildCare's Wildlife Hospital treats nearly 4,000 ill, injured and orphaned wild animal patients from over 200 species every year. This is one patient's story.

Barn Owl. WildCare photo by Alex GodbeThe Barn Owl had been banded as an owlet by a WildCare volunteer in 2005.

Eight years later, WildCare's Wildlife Hospital admitted the bird, and identified her by the federal band around her leg as a nestling we'd met before.

But the bird was dead on arrival at WildCare, and test results reveal she died of rat poisoning.

When young barn owls are present in an owl box, the Hungry Owl Project, a program of WildCare, sometimes weighs, measures and bands the nestlings as part of a long-term study. This particular owl had been banded in 2005 on a property in the Indian Valley area of Novato.

As a study result, it's fascinating to find out that this owl had done well, and had survived for eight years -- well beyond the average lifespan of a Barn Owl.

But her long and successful life was cut short when she ate a poisoned rodent. This happens a lot.

Is rat poison a problem in YOUR area?

WildCare's data indicate that the answer is probably yes.

WildCare tests our predatory animal patients -- animals that eat rats and mice -- for exposure to rat poisons. Our laboratory data document conclusively that a predator animal like this owl that eats a poisoned rodent ends up poisoned herself.

Of the 138 samples sent to the California Animal Health and Food Safety Laboratory (CAHFS) at UC Davis in 2013, an astonishing 76.8 percent of tested patients show some exposure to these toxic poisons.

The map below charts the location where WildCare patients that tested positive for rodenticide exposure have been found.

Because the majority of our patients do come from Marin County, the concentration of poisoned patients is centered in Marin, but the correlation is obvious. These poisons are being used everywhere and wild animals are paying the price.

WildCare map of where poisoned animals came from

WildCare's Rodenticide Diagnostics and Advocacy Program is a major research initiative in partnership with the Environmental Protection Agency, the Humane Society of the United States, the California Department of Pesticide Regulation, and the UC Davis California Animal Health and Food Safety Laboratory.

Together, we are working to eliminate dangerous rat poisons that affect wildlife, pets and people.

When an animal is admitted to WildCare's Wildlife Hospital, poisoning is not usually the obvious reason for admittance. The majority of our patients are hit by cars, caught by cats, otherwise injured or found without the tell-tale symptoms of rodenticide poisoning such as bleeding from the mouth or other orifices and conspicuous anemia.

But even without symptoms of anti-coagulant rodenticide poisoning, WildCare's data reveals that the majority of rodent-eating patients like hawks, owls, raccoons and foxes are carrying these toxins in their bodies.

And the impact is far-reaching. The various toxins stay in body tissues for a surprisingly long amount of time. Brodifacoum and bromadiolone, two of the most prevalent and toxic second-generation anti-coagulant rodenticides remain in body tissues for 217 days and 248 days respectively, which is one of the reasons so many WildCare patients test positive. These animals are simply unable to rid their bodies of the poisons.

Various studies have found these poisons in the fetuses of pregnant animals, and an increasing number of studies including this one on Notoedric Mange in Bobcats and Mountain Lions show clear links between rodenticide exposure and increased mortality from non-poison-specific causes.

So what do WildCare's data reveal?

The following numbers reflect species totals for WildCare patient rodenticide exposure in 2013:

Species Number of

positive tests

Number of
individuals tested
Barn Owl 9 11
Cooper's Hawk 2 3
Great Horned Owl 4 4
Northern Spotted Owl 1 1
Red-shouldered Hawk 9 10
Red-tailed Hawk 12 17
Saw-whet Owl 1 1
Sharp-shinned Hawk 1 1
Turkey Vulture 1 2
Western Screech Owl 3 3
White-tailed Kite 2 4
Crow 2 7
Raven 1 1
Gray Fox 13 14
Opossum 1 1
Raccoon 30 34
Striped Skunk 13 16

Four Gray Foxes. WildCare photo by Linda CampbellAs the above chart indicates, Barn Owls, Northern Raccoons and Gray Foxes are some of the animals most affected, according to WildCare's data.

Ironically, these three species are particularly adept at eating rodents and thus provide some of nature's best free rodent control. If you have raccoons and foxes moving through your yard, you likely do not have problems with rats and mice.

By allowing these predators to be poisoned, we are destroying the best chance we have at maintaining a natural balance of rodent populations.

The vast majority of tested animals must have received their rodenticide load through secondary poisoning, whereby an animal eating a rat dying of poisoning gets poisoned himself. Due to the nature of so-called "second generation" anticoagulant rodenticides, a rodent may take several days to die of dehydration and internal bleeding, during which time he may return to a bait box again and again.

Great Horned Owl patient. WildCare photo by Melanie PiazzaThese rodenticides are advertised to "kill in a single feeding" and, while no doubt the first feeding is what eventually kills the rodent, the time lapse between initial feeding and death means a dramatically higher toxic load builds up in the rodent's body tissues. By the time a Great Horned Owl eats that rodent, it has many times the lethal level of poison in its system.

Other animals in our 2013 testing data including the opossum and the crows probably encountered the poisoned bait itself and consumed enough to poison themselves. Domestic pets may also be poisoned the same way, and data from Poison Control Centers nationwide demonstrate that children can be poisoned too. (Click to read more about risks to children and pets.)

The data WildCare has been collecting on rodenticide prevalence since 2010 provide unequivocal proof that predatory wildlife is being poisoned from eating poisoned rodents. But more information was needed to complete the picture.

In August 2013, WildCare began a year-long research study in partnership with the California Department of Pesticide Regulation (DPR) on the effects of anticoagulant rodenticides on wildlife. This study will help researchers understand the ways in which rodenticides contribute to, or cause these animals' deaths. With DPR's support, we are now requesting necropsies of deceased patients to determine not only if the animal has rodenticides in his system, but also if the toxic load was the actual cause of the animal's death, or just a contributing factor.

The second component of the study will be to determine exposure levels of rodenticides in domestic animals.

Data from WildCare's testing protocols is a critical contribution to the field and will help biologists and conservationists around the country to inform consumers that the evidence of far-reaching environmental havoc from these incredibly toxic poisons is mounting.

How to Control Rodents Humanely

Rodents are an integral part of the environment, and they are the primary food source for most of the predatory animals in our area. It is not possible, nor is it desirable, to eradicate rodents outside.

However, most people do not want rodents inside their homes or damaging their property. The following information will help you effectively eliminate rodent problems without resorting to the use of rat poisons.

The best method of rodent control is prevention. Rodents tend to set up camp in our homes and businesses when food and space are made available to them.

Remove potential rodent homes like yard debris, trash, construction waste, etc. Remove ivy from on and near structures. Consider removing dense ground-covering plants too.

Eliminate food sources. Keep your garbage completely sealed with lids closed and secured. Keep bulk food, seed, and dry pet food in metal cans with secure lids. Pick up fallen fruit. Take birdfeeders inside at night.

Exclude rodents from your home. Seal openings 1/2 inch or larger around the outside of your house with metal, concrete, or Stuf-fit Copper Mesh Wool, which can be found online or at hardware stores.

Include natural rodent predators in your solution. A family of five owls can consume up to 3,000 rodents in breeding season. Placing a nest box to encourage a family of owls to make your property home can be a great alternative to commercial pest control methods. DO NOT erect an owl box if you or anyone in your neighborhood is using poison, however. Please visit hungryowl.org for more information.

Use catch-and-release traps as a safe, sanitary, and humane solution. Catch-and-release traps will allow you to remove rodents from inside your home, but you must prevent their return by sealing entrance and exit holes and removing attractants (see above). Remember it is illegal in the state of California and cruel to relocate animals (click to learn why), so trapped rodents should be deposited outside once entry points have been sealed.

WildCare is a 501(c)3 nonprofit organization supported almost entirely by private donations and individual memberships. Visit us online at wildcarebayarea.org.