Restricting Rodenticides Saves Wildlife From Slow Poisoning Deaths
1. 8 MAY—JUNE 2014
POISON
The use of second-generation anticoagulants, com-
monly found in rodenticides, faces new restrictions
on how and who can administer its usage. The
change in who can use such toxic chemicals comes
as a result of collateral deaths to wildlife. Since ro-
dents are a staple of their diets, raptors, foxes and
bobcats are the most frequent victims of second-
ary poisoning. Here, a trio of Norway rats (Rattus
norvegicus) emerging from hole in a suburban yard at
night. The Norway rat occur in the Central Valley, urban
coastal areas and the Lake Tahoe area.
3. 10 MAY—JUNE 2014
Wildlife applauded DPR’s decision. For
decades, CDFW’s environmental scientists
have witnessed the suffering and death
from SGARs when non-target animals and
birds eat poisoned rodents.
Not everyone has seen the decision as
beneficial and some voice concern over
being overrun with what they fearfully
describe as disease-ridden vermin. But the
notion is unrealistic. There remain numer-
ous ways to deal with rodents without
harming non-targeted animals. (See sidebar,
Non-Toxic Rodent Controls are Available)
DPR’s decision restricts only four
chemicals that are most likely to cause
the secondary poisoning of animals other
than rodents. The chemicals include the
SGARs brodifacoum, bromadiolone, difena-
coum and difethialone. Scientists have de-
termined these are more toxic and longer-
lasting than older rodenticide compounds.
The popular rodent baits made with
SGARs promised to kill rodents with only
one feeding. What most inexperienced
users failed to understand was that the poi-
son worked slowly with terrible collateral
results. In the several days that it takes for
the SGARs to work, the rodents continue
to eat the bait, which concentrates toxins
in their bodies before they die. Meanwhile,
their natural predators still see them as a
tasty meal, and while weakened, they’re
easy to catch.
When predatory and scavenging birds
and mammals eat the dead or dying ro-
dents that have consumed these baits, the
predators can become poisoned. Common
victims include all types of wildlife: owls,
hawks, raccoons, bobcats, mountain lions,
foxes and coyotes. In two cases, tertiary
poisoning occurred when mountain lions
ate coyotes that had eaten rodents that
had eaten anticoagulant rodenticide bait.
This is how toxins work their way up the
food chain.
The chain does not limit itself only to
wild animals. House pets that are allowed
to roam will also eat dead or dying rodents
that have eaten the bait, or in some cases
have eaten unprotected bait themselves,
with the same results. Veterinarians have
treated dogs and cats that have ingested
just enough poison to make them sick,
but not kill them. According to the Marin
Humane Society says dogs are especially
susceptible to these toxins, and d-CON has
been used to intentionally poison pets.
Poison control centers report approxi-
mately 10,000 U.S. children are exposed to
rodenticides every year. The U.S. Environ-
mental Protection Agency cited that figure
when, in 2011, it required all rodenticides
intended for above-ground residential use
be placed in bait boxes.
CDFW Research Made
the Connection
CDFW scientists have been study-
ing dead wildlife for decades with par-
ticular interest in evidence of poisoning
by legal pesticides since at least 1994. By
1998, CDFW scientists thought there was
enough evidence of widespread rodenti-
PhotoscourtesyoftheU.S.NationalParkService
National Park Service biologists Joanne Moriarty and Jeff Sikich, top image, measure
a captured mountain lion’s incisors in late March. The big cat was treated for mange,
bottom image, a parasitic disease of the hair and skin. Blood tests later showed
exposure to anti-coagulant rodenticides, commonly known as rat poison.
4. OUTDOOR CALIFORNIA 11
cide poisoning in non-target wildlife to ask
the DPR to restrict the use of brodifacoum,
one of the four culprits, to certified profes-
sional users. DPR estimates that 98 percent
of brodifacoum is used by unlicensed peo-
ple such as homeowners and maintenance
workers. The perception might be that
people whose livelihood requires a profes-
sional license are more likely to be trained
and use toxic products only as directed to
ensure an acceptable level of safety.
“When SGARs, which are lethal with
one feeding, became available for home-
owner use, the department started receiv-
ing more reports of poisoned non-target
wildlife,” said Bob Hosea, a CDFW envi-
ronmental scientist who did research on
rodenticide-poisoned wildlife from 1994 to
2006. Since rodents are a staple of their di-
ets, raptors, foxes and bobcats are the most
frequent victims of secondary poisoning.
As investigations proceeded, CDFW
received carcasses of dead animals from
wildlife care facilities. Researchers discov-
ered that in a large radio telemetry study
along the Coast Range in the San Francisco
Bay area, golden eagles were found to have
been exposed to SGARs. Mountain lions
and bobcats from the Thousand Oaks area
had been exposed as well. A dead moun-
tain lion that had been exposed was found
in Palm Springs. In each case, the question
became how could animals like mountain
lions and golden eagles be exposed to these
pesticides if they were only to be used
inside and adjacent to buildings?
Most disturbing was the discovery
that 73 percent of San Joaquin kit foxes—
a protected species under both state and
federal law—that were recovered from the
unique urban population in Bakersfield,
had been exposed to these compounds.
Environmental scientist Stella McMil-
lin has directed anticoagulant research for
CDFW since 2006. “When animals die of
anticoagulant poisoning, it is often obvi-
ous,” she said. “Sometimes you can see the
bruising even before you open the carcass.
There’s a lot of blood inside the bodies
from the internal hemorrhaging antico-
agulants cause.”
Other external signs may include
blood oozing from the legs and mouth
of birds and mammals, from the nose in
mammals and red bruises from blood run-
L
ike most animals, rodents go where
food is available and they feel safe.
So the easiest way to discourage
them is to remove or modify any-
thing that could make them comfortable.
Sanitation is the first step to controlling
rodents. Without sanitation, all your other
efforts will be wasted and rats will return.
Food
Norway rats eat a wide variety of foods
but seem to prefer cereal grains,
meats, fish, nuts and some fruits. Roof
rats will eat those things, but they prefer
fruits, nuts, berries, slugs and snails. They
are especially fond of avocados and citrus.
Both species will eat your pets’ food—an
easy meal.
• Pick up fruit that has fallen from trees
as soon as possible.
• If you have any kind of dry pet food,
bulk food (i.e., rice) or seeds, keep
it in metal containers with tight lids,
especially if you store it in a garage
or shed. Rodents can chew through
almost anything else.
• Never leave any food out (human
or pet), especially outside or in the
garage.
• If you have a bird feeder, put it on a
slick metal pole and take it indoors at
night.
• Secure your garbage in a tightly sealed
can.
• Seal water leaks and remove standing
water that can attract unwelcome
animals (and waste water.)
Remove “Guests”
Seal all the entries to your home, but
first, make sure there are no rodents
that could be trapped inside. Dead animals
inside a wall or attic will stink! Trap and
remove any rodents that are already there.
Set traps in secluded areas where they’ve
been seen or are likely to travel, such as
close to walls, behind objects, in dark cor-
ners, on ledges, shelves, fences, pipes and
garage rafters. In areas where children, pets
or birds might go, put the trap inside a box
or use some kind of barrier to keep them
away from it.
Check traps daily and wear disposable
gloves when removing rodents from traps;
place them in a sealed plastic bag then into
your garbage bin for weekly collection.
Wash your hands after handling traps or
rodents, even when using gloves.
Exclusion
Seal all openings where cables, wires and
pipes enter buildings, and any cracks
or holes in foundation, walls and roofs
with hardware mesh and concrete, plaster
or metal whenever possible. Rodents can
squeeze into holes that are as narrow as
a half-inch in diameter. At the very least,
stuff stainless steel or copper pot scrub-
bers or Stuf-fit copper mesh wool into the
spaces. All are sold online and at hardware
and discount stores. Norway and roof rats
can chew through polyurethane spray foam
fillers, wood, sheet rock, caulking and plas-
tic sheeting.
• Repair or replace any damaged ventila-
tion screens under eaves or around the
foundation of your home.
• On windows that can be opened, keep
screens in good condition; repair holes.
• Cover rooftop plumbing vent pipes
and attic vents with screens.
• Whatever method you use, check your
work periodically, so you can repair it
if it weakens or gets damaged.
Support Nature to
Support You
Protect rodents’ natural predators—birds
of prey. Providing tall trees that owls
and other raptors favor will encourage
them to hang around your yard and remove
rodents for you.
• During breeding season, a family of
five owls can eat as many as 3,000
Non-Toxic Rodent
Controls are Available
Non-Toxic Controls
Continues on Page 19
5. 12 MAY—JUNE 2014
ning freely under the skin on all animals.
The animals’ bodies are checked for
evidence of trauma that would indicate
another cause of death. But even animals
killed in other ways often have antico-
agulants in their systems. Sick or dying
animals are more vulnerable than healthy
ones to injuries and death by other means.
“Back in the 1990s, it was easier for our
findings to be discounted,” McMillin said.
“But now multiple studies by different
researchers have shown the same thing.
Whether it’s mountain lions and bobcats,
fishers, raptors or kit foxes, our wild preda-
tors and scavengers are being exposed to
SGARs at very high rates.”
Rat poison in
old-growth forests?
A 2012 study entitled Anticoagulant
Rodenticides on our Public and Community
Lands: Spatial Distribution of Exposure and
Poisoning of a Rare Forest Carnivore revealed
significant impact on fishers (Martes pen-
nanti). The fisher once lived throughout
the West Coast of North America but is
now a candidate for listing under the fed-
eral Endangered Species Act. The conclu-
sion drawn was that the rodenticide that’s
killing them is almost certainly being used
by people illegally growing marijuana on
public and private lands.
When CDFW’s Chief of Enforcement
Mike Carion took the helm as the state’s
top wildlife officer and the leader of
California’s warden force, he inherited a
problem that had been around for a long
time, but was taking on a new high-profile
status. “Illicit marijuana grows are wreak-
ing havoc on our wildlife and the habitat
they need to survive,” he said. “Illegal
marijuana grows have huge impacts on
the environment, not only through illegal
stream dewatering and habitat destruc-
tion, but also by the use of pesticides like
d-CON to protect the crops. Many of the
pesticides are not even legal for use in the
United States. It’s devastating for wildlife.”
There may also be a connection
between non-lethal rodenticide poisoning
and mange in some species. National Park
Service wildlife ecologist Dr. Seth Riley led
a study to determine whether there is a
correlation between anticoagulant expo-
sure and notoedric mange in bobcats and
mountain lions in Southern California.
The animals in Santa Monica Moun-
tains National Recreation Area were
studied between 1996 and 2006. Blood
and liver tests indicated that 90 percent
of the mountain lions and 92 percent of
the bobcats had been exposed to roden-
ticide—often more than one type. If the
poison doesn’t kill them outright, it tends
to lower their resistance to disease, which
can result in a form of mange that causes
dehydration and a slow, painful death.
“They have
a crusty face and
head, and become
emaciated,” Riley
said. A significant
number of mortali-
ties and declines in
population have
been noted in bob-
cats in the Malibu
area because of rat poison. All the cats with
mange also had anticoagulants in their
systems.
Two collared mountain lions—part
of 31 lions involved in the Riley study—
were killed by rat poison, researchers have
learned. Both lions had killed and eaten
coyotes in the previous month. Necropsies
indicated the lions were poisoned by the
coyotes they ate, and that the coyotes
carried high levels of rodenticide toxins
“Some people do read the labels but think
if they use twice as much as directed, it
will be twice as effective. That is absolutely
wrong!”
Bob Hosea
CDFW Environmental Scientist
6. OUTDOOR CALIFORNIA 13
from the rodents they ate.
A target pest can continue
to consume bait before it
dies, causing super-lethal
SGAR concentrations to
accumulate in its body.
Predators and scavengers
that consume such rodents
are then exposed to very
high doses of these toxic
compounds.
The first-ever cases of
mange in San Joaquin kit foxes occurred in
Bakersfield last year. It is unknown wheth-
er there is a connection between mange
and SGAR exposure. What is known is that
last year at least three of the endangered
foxes died from SGAR poisoning and an
additional five died from mange. All of
the foxes that died of mange had been
exposed to SGARs. Evidence shows that
most of the animals were exposed to more
than one kind of SGAR. Scientists at the
CDFW Wildlife Investigations Laboratory
and California State University-Stanislaus
Endangered Species Recovery Program
studied kit fox habitat use to try and deter-
mine potential sources for anticoagulant
exposure. The foxes that tested positive for
SGARs were more likely to be found near
golf courses and undeveloped areas—de-
spite the fact that SGARs are labeled only
for use in and within 100 feet of build-
ings. These results support the theory that
people are using the SGARs in the wrong
settings, in violation of the instructions
on the products’ packaging. (The study is
online at http://digitalcommons.lmu.edu/
cgi/viewcontent.cgi?article=1144&context=
cate.)
“Some people do read the labels but
think if they use twice as much as directed,
it will be twice as effective,” Hosea said.
“That is absolutely wrong!”
New Restrictions
Can Save Wildlife
Because of hazards documented by
the late 1990s, the U.S. Environmental
Protection Agency (EPA) was considering
restrictions on such products at the same
time as DPR. The chemical industry lob-
bied against new state regulations and con-
vinced DPR to wait for the federal agency’s
decision.
“Rodenticide manufacturers were
asked in June 2008 to adopt the safety
measures – bait stations and formulation
changes,” the EPA said. “They were given
three years—until June 2011—to make the
changes, and most manufacturers met that
deadline. Reckitt Benckiser, the manufac-
turer of d-CON, is the only rodenticide
manufacturer that is currently producing
and selling products that do not meet the
current safety standards.”
The current standards for products
that contain SGARs and are marketed to
residential consumers throughout the U.S.
are:
• Bait stations must be protective and
tamper resistant. Only bait forms that
can be secured in bait stations, like
blocks or pastes, may be used in these
products.
• Products may contain no more than 1
pound of rodenticide bait.
• Active ingredients may not contain
the second generation anticoagulants
brodifacoum, bromadiolone, difena-
coum or difethialone.
The EPA has been moving to ban
household sales of products containing
brodifacoum by canceling the legal reg-
istration of products that do not comply
with these safety requirements (www.epa.
gov/pesticides/mice-and-rats/). Without
legal registration, such dangerous products
cannot be sold to unlicensed consumers in
the U.S.
Twelve d-CON mouse and rat poisons
will be affected by this, so the manufactur-
er, Reckit Benckiser, has stopped fighting
and negotiated an agreement with the
EPA. According to their news release, the
company “will voluntarily discontinue
production of d-CON baits containing
second generation antico-
agulant rodenticides. Those
rodent control products
will be replaced with a new
line of rodenticide baits
in 2015, which have been
registered with the U.S. EPA
and are approved for con-
sumer use in every state,
including California.”
California won’t wait
another six months to get
the most dangerous rat poisons off store
shelves. DPR’s new restrictions take effect
in July.
The California Office of Administra-
tive Law approved DPR’s new regulations
in March, making all SGARs restricted
materials. The following week, Reckitt
Benckiser sued DPR for restricting d-CON’s
active ingredients to certified pest control
professionals and sought to delay imple-
mentation of the new rules. A California
Superior Court denied that request on May
9.
As stated in DPR’s Initial Statement of
Reasons, restricting the use of all SGARs
to only certified pest control profession-
als will significantly reduce unintended
exposures to non-target wildlife. Certi-
fied applicators will ensure that SGARs
are properly used, placed and monitored,
and that poisoned rodents are disposed of
properly.
It’s believed that certified applicators
generally perform qualitative site assess-
ments to determine how to effectively
control the target species. SGARs are only
one of several tools certified applicators
may use for effective rodent control. In
contrast to general consumers, certified ap-
plicators are more likely to implement in-
tegrated pest management (IPM) strategies
and use non-pesticide measures—especially
preventive strategies—before resorting to
pesticides. Licensees and permit holders
have more requirements related to such
strategies than non-certified applicators.
For example, IPM strategies are covered in
the certification examination process and
continuing education courses attended by
certificate holders and licensees.
The DPR and EPA are not acting
rashly. Six years have passed since the EPA
Rat Poison
Continues on Page 19
״We’ve asked for tighter regulation of brodifacoum
for nearly 20 years because of evidence that wildlife
was being poisoned. In that time, Reckitt Benckiser
could have employed scientists to develop safer
alternatives, but instead chose to employ lawyers to
stall the process.״
Stella McMillin
CDFW Environmental Scientist
7. OUTDOOR CALIFORNIA 19
Rat Poison
Continued from Page 13
imposed the new safety requirements.
Every rodenticide manufacturer com-
plied except Reckitt Benckiser. Now these
agencies must take action for the safety of
non-target animals and people.
“We’ve asked for tighter regulation
of brodifacoum for nearly 20 years be-
cause of evidence that wildlife was being
poisoned,” McMillin said. “In that time,
Reckitt Benckiser could have employed
scientists to develop safer alternatives, but
instead chose to employ lawyers to stall
the process.”
Safe, Effective
Rodent Control
There’s more than one way to keep
rodents away, and some are safer than
others. CDFW urges residents to employ
non-chemical means of rodent control in
order to protect the state’s wildlife.
“The best way to keep rodents out of
your home is by eliminating access points
that rats and mice might use to enter,”
McMillin said. “It can be as easy as stuffing
stainless steel or copper pot scrubbers, or
Stuf-fit copper mesh into small holes.”
More information on protecting wild-
life and pets from rodenticide baits is on
CDFW’s website at www.dfg.ca.gov/educa-
tion/rodenticide.
Dana Michaels is a marketing specialist with the
California Department of Fish and Wildlife. Her
stories have appeared before in Outdoor California.
rodents. You can encourage them
by hanging a nest box on your
property. Be cautious, however,
and don’t do this if you or any
of your neighbors are using any
kind of rat poison. Remember that
poisoned rodents can poison the
predators, scavengers and pets
that eat them.
No Rat Habitat
Keep your home and yard neat and
clean. Don’t give rats places to
hide.
Remove things rodents can hide
under, such as wood piles, debris, con-
struction waste, dense vegetation and
ground-covering vines, like ivy.
Resources for More Information
To learn more about owl nest boxes, visit
www.hungryowl.org
Raptors Are The Solution (RATS): www.
raptorsarethesolution.org/
University of California Integrated Pest
Management: www.ipm.ucdavis.edu/PMG/
PESTNOTES/pn74106.html#MANAGEMENT
Find your county’s UC Cooperative Ex-
tension office for local advice at http://
ucanr.edu/County_Offices/
For safer, legal rodent bait station prod-
ucts visit: www.epa.gov/pesticides/mice-
and-rats/rodent-bait-station.html
Non-Toxic Controls
Continued from Page 13
Researchers removed only 93 ticks
from one reptile, one bird and seven mam-
mals, a number substantially less than
what would be expected had animals been
found in rural instead of urban areas. Ticks
included three infamous human-biters
and disease carriers: the western black-
legged tick, the Pacific Coast tick and the
American dog tick. These ticks have broad
feeding habits—the western blacklegged
tick alone dines on 108 species of lizards,
birds or mammals. It is the primary carrier
of two bacteria that cause human diseases
in the far western United States: Lyme dis-
ease and the rarely acquired granulocytic
anaplasmosis.
Gray fox was the most heavily para-
sitized animal as six of only 29 animals
yielded more than half of all ticks enumer-
ated. Nearly 100 wild turkeys were deemed
tick-free, but previous research revealed
that rural turkeys are an important host
of nymph western-blacklegged ticks in
Sonoma County.
Researchers rejoiced over some discov-
eries in the study. Two canines, a coyote
from Livermore of Alameda County and
a gray fox from Lafayette of Contra Costa
County, exhibited signs of tick paralysis.
Tick paralysis is a serious, crippling and
sometimes fatal disease affecting pets,
livestock, wildlife and occasionally people.
The paralysis is caused by a toxin secreted
in the saliva of certain female ticks while
feeding. The disease in wild canines resem-
bles that in dogs. It begins with incoordi-
nation and an ascending, flabby paralysis
in the rear legs. In more severe cases, the
paralysis progresses to the front legs. The
treatment is simple—find and remove
any attached ticks before their toxin may
claim the animal’s life. After tick removal,
the victim usually makes an uneventful
recovery within two days. The partially
paralyzed coyote and gray fox recovered
fully and were released.
This is the first published report in the
United States of tick paralysis in a natural-
ly infested coyote, and only the third case
recorded in a gray fox. Ticks from the coy-
ote were not saved because that animal’s
disease onset predated the current survey.
Ticks removed from the fox were adult
American dog ticks, an aggressive human-
biter commonly causing tick paralysis in
dogs in the Sierra Nevada foothills. Akin
to dogs, coyotes and foxes are preferred
hosts of adult American dog ticks. Since
many afflicted animals escape detection,
tick paralysis may have a more deleteri-
ous impact upon wild-canine populations
than realized.
Molecular testing likewise produced
some intriguing results. Eight ticks found
attached to mammals contained Lyme
disease bacteria or a relapsing fever bac-
terium that can infect humans. The ticks
were removed from the paralyzed gray
fox from Lafayette, another gray fox from
Orinda and a brush rabbit from Martinez,
all of Contra Costa County, and a rac-
coon from Tracy in San Joaquin County.
These telltale discoveries inform wildlife
rehabilitators, health-care providers and
veterinarians that wildlife, people or their
pets can be exposed occasionally to tick-
transmitted zoonotic bacteria in metro-
politan areas of the greater San Francisco
Bay region.
As Heckly opined, “many opportuni-
ties exist for the research community to
use animals brought to wildlife rehabili-
tators.” The yearlong survey of ticks on
urban wildlife exemplified that approach,
and opened new doors between research-
ers and facilities like the Lindsay Wildlife
Museum. It also produced some compel-
ling findings of wildlife-medical or public
health significance. And, it was made
possible by the diligent efforts of the staff
at the Lindsay Wildlife Museum.
Robert S. Lane is a Professor Emeritus of Medi-
cal Entomology at the University of California,
Berkeley. He studies the biology of ticks and
the ecology and epidemiology of tick-borne
diseases. His stories have appeared before in
Outdoor California.
