Two owlets born at Sweet Springs Nature Preserve in Los Osos.
Photo courtesy of Morro Coast Audubon Society

Test results confirmed that a deceased great horned owl found at the Morro Coast Audubon Society’s Sweet Springs Nature Preserve in Los Osos was poisoned.

There has been a breeding pair of owls at Sweet Springs Nature Preserve for at least 10 consecutive years. In April, a male was discovered bleeding and died the following day.

The CA Dept. of Fish and Wildlife recently confirmed that the owl died as a result of ingesting anticoagulant rodenticide.

“Testing has been completed on the great horned owl,” said Fish and Wildlife Senior Environmental Scientist Krysta Rogers in a report. “Three different anticoagulant rodenticides were detected in the owls’ liver including Brodifacoum and Difethialone, at relatively high levels, and Bromadiolone, at a trace amount. Given that there was evidence of coagulopathy in the absence of trauma and anticoagulant rodenticides were detected in the liver, cause of death for this owl was anticoagulant rodenticide toxicosis. All three of the rodenticides detected are second generation anticoagulant rodenticides and must be applied by a certified applicator (e.g. pest company) for use in or around buildings or other structures.”

Rodenticides kill rodents by causing them to hemorrhage. This is not an immediate death. The rodents come out of their burrows looking for water. They are weakened and thus are easy prey for predators such as owls, hawks, foxes, even cats and dogs. The poison is passed on to the animal that eats the poisoned rodent. These poisons do not break down for months, some for more than a year, poisoning every animal that eats a poison-weakened animal.

For example, one week after the adult owl died, one of two owlets was found in poor condition on the ground nearby. It was taken to Pacific Wildlife Care (PWC).

“An animal can kill all of its young by bringing back poisoned rodents, or alternatively, the parent eats poisoned rodents, dies and the babies starve since there is no one to feed them,” said Judy Neuhauser, president of the Morro Coast Audubon Society.

“We actually found the other owlet, or perhaps I should say we found what was left of it — feathers and a few bones. The question for that one is: how did it die? If it died of rodenticide poisoning, did the poison now move into the scavenger (fox, cat, dog, coyote, skunk, possum, vulture)? These rodenticides can stay in the liver of the affected animal for up to 120 days — that is 4 months.”

In the case of another owlet, a vet suspected anticoagulant rodenticide poisoning and began treatment with Vitamin K, which saved the life of this little owlet that continues to be cared for in the rehabilitation unit at PWC. The owl has gained weight and is no longer receiving Vitamin K treatment for coagulation problems. Being released back into nature is the ideal outcome

“The question of release is a bit more complicated. These owls stay with their parents for an extended period of time, up to several months,” said Neuhauser. “PWC usually likes to release animals where they were found, but this owlet does not have parents to feed him and teach him. They also would prefer to release in a relatively safe environment. Considering the history of rodenticide poisoning in this area, it is unclear where they would release him.”

The local owl is one of many such victims throughout the state. Last October, 21 environmental organizations sent a request to Governor Newsom for an emergency moratorium on these products while the California Department of Pesticide Regulation reevaluates the products as the result of a lawsuit filed by Raptors Are The Solution in 2018.

“There is not presently a moratorium on these rodenticides,” said Neuhauser. “We would like for there to be a moratorium.”

Although the state pulled these products from consumer shelves in 2014, professional companies are allowed to use them. Rat poison has infested the food web, from owls to hawks to cats, dogs, mountain lions, bobcats, and endangered species like the Pacific fisher.

These raptors are efficient predators. They can each kill and eat over 30 rats every month. By inadvertently poisoning these raptors, we are killing off our best natural predator controls.

Not all the news is bad for birders and ornithologists here on the North Coast. Breeding is necessary to the survival of a species and nature may be taking its course at Sweet Springs.

“Two adult great-horned owls were seen near the Preserve in the past couple of days,” said Neuhauser. “It is possible that the female has found a new mate, though it is late in the year for a new nesting attempt. If they stay in the area — and do not succumb to rodenticide poisoning — we may have a mating pair again next year.”

Morro Coast Audubon Society has about 900 members. For more information, go to https://www.morrocoastaudubon.org/
Other Ways to Keep Rodent
Populations Under Control For the past 10 years, many California cities have managed their rodent problems using alternatives to second generation anticoagulants. Some pest control companies have switched to traps, exclusion, or other less damaging rodent control products.

The first step is to assess the area and remove rodent attractions.
• Remove access to any other food source. Bring pet food in at night, keep garbage in a tight container, clean up spilled bird seed and fallen fruit.
• Keep dense mats of vegetation – such as ivy – away from the house foundation. Ivy provides not only shelter, but also food (snails) and water to rodents!
• Determine where the rodents are entering your house/garage/storage shed. Plug any holes.
Traps: With all traps, you can feed your bait without setting the trap for a few days to accustom the rodents to the trap before you actually set the trap. The dead rodents from these traps are non-toxic to any predator that might eat the dead rodent, so there is no secondary wildlife poisoning.
• Snap traps: These come in sizes for both rats and mice. The best location to place them is in a hidden area next to a wall. Rats and mice prefer to keep their bodies in contact with their world, and therefore tend to scurry along walls or dense vegetation rather out into an open space. Change up the bait if they stop taking the one you offer. Keep these away from areas your pets, other wildlife, and chil
• Zapper traps: These use batteries to electrocute the rats or mice resulting in a quick death. They cost around $45 and need to have the batteries replaced or recharged often. They are quite effective.
• GoodNature A24 CO2 Trap: This trap uses a CO2 canister to power a piston that kills the rat or mouse instantly. The trap has the advantage that it “resets” and is ready to go again immediately. It can kill up to 24 rats before needing a new canister. This is rather expensive, but has the advantage of killing many rats/mice in a single night.
• Never use sticky traps – they also trap hummingbirds and other small birds!
• Attract Barn Owls with a nest box. A single Barn Owl can catch 1,400+ rodents a year!
For more information: https://www.raptorsarethesolution.org

For the past 10 years, many California cities have managed their rodent problems using alternatives to second generation anticoagulants. Some pest control companies have switched to traps, exclusion, or other less damaging rodent control products.

The first step is to assess the area and remove rodent attractions.
• Remove access to any other food source. Bring pet food in at night, keep garbage in a tight container, clean up spilled bird seed and fallen fruit.
• Keep dense mats of vegetation – such as ivy – away from the house foundation. Ivy provides not only shelter, but also food (snails) and water to rodents!
• Determine where the rodents are entering your house/garage/storage shed. Plug any holes.
Traps: With all traps, you can feed your bait without setting the trap for a few days to accustom the rodents to the trap before you actually set the trap. The dead rodents from these traps are non-toxic to any predator that might eat the dead rodent, so there is no secondary wildlife poisoning.
• Snap traps: These come in sizes for both rats and mice. The best location to place them is in a hidden area next to a wall. Rats and mice prefer to keep their bodies in contact with their world, and therefore tend to scurry along walls or dense vegetation rather out into an open space. Change up the bait if they stop taking the one you offer. Keep these away from areas your pets, other wildlife, and chil
• Zapper traps: These use batteries to electrocute the rats or mice resulting in a quick death. They cost around $45 and need to have the batteries replaced or recharged often. They are quite effective.
• GoodNature A24 CO2 Trap: This trap uses a CO2 canister to power a piston that kills the rat or mouse instantly. The trap has the advantage that it “resets” and is ready to go again immediately. It can kill up to 24 rats before needing a new canister. This is rather expensive, but has the advantage of killing many rats/mice in a single night.
• Never use sticky traps – they also trap hummingbirds and other small birds!
• Attract Barn Owls with a nest box. A single Barn Owl can catch 1,400+ rodents a year!

For more information: https://www.raptorsarethesolution.org