Download Invader of the Month: Feral Cats

The Domestic Cat: Felis catus
Invasive Species of Concern in Maryland
Invader of the Month: Feral Cats
ANNAPOLIS, MD (April 15, 2010)
Feral cats (Felis catus) are a perfect
invasive species. They are nonnative to North America, have a high
reproductive rate, relatively low
mortality, and high dispersion rates.
They also have the ability to be cute
and cuddly, a perfect shield from
those that wish to do them harm.
Photo by James Morton
Brian Clark, University of Maryland Extension
Cats are the purrfect hunter, a mix of
power, stealth, and speed.
Domesticated cats are simply scaled
down versions of their larger
cousins. As a domesticated species, they have put their hunting capabilities to good use,
protecting our health and property from rodents that would destroy what we have.
However, when these cats are released into the environment on a permanent basis, they
can disrupt the balance of an already fragile ecosystem. When cats are first released into
the environment, they are generally referred to as strays, and can be reincorporated into
domestication with little difficulty. As the generational gap increases between domesticated and non-domesticated, adult feral cats are less likely to be re-domesticated.
However, small cats are not part of the native food web in North America and can wreak
havoc on an ecosystem. It is believed that between 50 and 100 million feral cats roam the
United States, with 70 million being a conservative consensus among experts. Small
mammals such as mice and moles make up a majority of their prey. Even with their ability
to fly, birds, especially nestlings or fledglings, make up approximately 20% of a feral cat’s
prey. During a study of feral cats in Wisconsin, a single cat averaged 3.1 animal kills each
day. If each cat kills one animal, each day, up to 36.5 billion animals could be killed by
feral cats each year. Feral cats can take a toll on native wildlife, decimating populations
already under stress due to habitat shrinkage. Their hunting abilities are used on rodents,
birds, insects, reptiles, amphibians, and even fish. The number and size of prey that a small
cat can bring down will amaze you. Even full grown rabbits can be killed. Supplemental
feeding of feral cats is not an answer. Even well-fed feral cats will capture and kill, but not
always eat, their prey.
Many of the feral cat’s other nuisance habits can be attributed to mating behaviors. These
behaviors include noise from fighting and mating, and the smell from their pheromone-
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The Domestic Cat: Felis catus
laced urine. When they come into contact with roaming domesticated cats, there is also the
chance for the spread of diseases like rabies and parasites, such as fleas.
For those who love all animals, this presents a huge problem. Do you control the feral cat
or not? Failure to control a highly predatory, non-native species that has proven to kill
many of the small native species we enjoy is a necessity to preserve the overall balance of
an ecosystem. But to kill a cat, an animal that so many people love, is a political nightmare
for farmers and environmentalists.
Control can be a tricky issue. The first step is to prevent the release of new cats into the
environment. If you are unable to care for your cat, adoption is preferred. An animal
shelter is the next best and often legally the only other option. The next step is dealing with
existing populations of feral cats. Many people are protective of feral cat colonies. There
are hundreds of organizations out there that offer education to the public and protection to
the cats. The two most common control measures are trap-euthanize or trap-neuter-return
(TNR). Euthanizing feral cats is a method used primarily by government institutions, as it
provides control with the lowest cost. TNR is the procedure most recommended by feral cat
advocates.
Then there is the cycle of life. Feral cats themselves are hunted. Large hawks and owls will
fly off with the smaller individuals. Coyotes will often kill cats which compete for their food
resources. The reemergence of coyotes into Maryland should prove interesting to examine
over time.
Love your pet. Take care of the native environment. Spay or neuter. Keep your cats
indoors.
For more information about this and other Invasive Species of Concern, visit
www.mdinvasivesp.org
Source:
 Clark, Brian. Invader of the Month: Feral Cats. (Maryland Invasive Species Council, USDA APHIS PPQ Cooperative
Agricultural Pest Survey, April 15, 2010). Online at
http://mdinvasivesp.org/archived_invaders/archived_invaders_2010_04.html
What are feral cats? And what do
we call cats that are pets? What
about pet cats that can go outdoors?
Use the chart at right to see the differences
between indoor cats, limited range cats,
free-range cats, and feral cats 
Table 1 Source:
Hildreth, A.M., et al. 2010. Feral Cats and Their Management. University of Nebraska, Lincoln Extension. Online at
http://www.ianrpubs.unl.edu/epublic/live/ec1781/build/ec1781.pdf
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The Domestic Cat: Felis catus
Geographic Range
The domestic cat (Felis catus) evolved from the domestication of an ancestral wild species
(the African wild cat, Felis silvestris lybica) about 3,000 years ago. In the 1700’s and 1800’s,
ships carried cats to control rat infestations, and this was a major factor in early introduction of an invasive species. Today, humans bring cats as pets, and may leave the cats
behind, or kittens may disperse.
The Humane Society of the US
estimates that
one pair of breeding cats and
their offspring can produce
400,000 cats in seven years!
Cat Biology
Domestic and feral cats are distributed across
the United States, and are well adapted to living
in both urban and rural areas, in a wide variety
of settings (for example, in houses, under
(Assuming ideal conditions and
none die).
bridges, within forests, along creeks, and in
Source: Loss, S.R. et al. 2013. The impact of free
sewers. They may weigh from 3 to 8 pounds or
ranging cats on wildlife of the United States:
Nature Communications.
more, and are from 22 to 36 inches long. (Male
cats are usually larger and heavier than female
cats). The average life of a feral cat is 2 to 5 years; cats that are owned by people have a
life expectancy of 15 years.
A female cat reaches reproductive maturity between 7 to 12 months of age. Feral cats can
produce up to 3 litters each year, and litters generally include 2-10 kittens. Mating and
reproduction season for cats is spring and summer; the gestational period is 65 days.
Female cats care for their kittens in a den for about seven months, and then the family unit
breaks up and the young cats are on their own.
Ecological Impact
Biologists at the University of Georgia found that outdoor cats that killed did so once every
17 hours. The researchers attached small video cameras to 60 outdoor domestic cats in the
city of Athens, Ga., and recorded their outdoor activities during all four seasons.
In the US, cats are one of the top ‘super-predators’ of
wildlife, and their most significant impact is on bird
populations. On a global scale, cats have caused the
extinction of at least 33 bird species from around the
world, and kill about 480 million birds per year.
Approximately one-third of the birds killed each year
are killed by domestic cats (pets), not feral cats.
Cats prey on wildlife.
Photo by Stephen M. Vantassel
http://www.ianrpubs.unl.edu/epublic/l
ive/ec1781/build/ec1781.pdf
Scientists from the Smithsonian Conservation Biology Institute and the
U.S. Fish and Wildlife Service estimate that domestic cats in the United
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The Domestic Cat: Felis catus
States, including pets that spend part of the day
More birds and mammals
outdoors and strays and feral cats, kill 1.4±3.7
die at the mouths of cats
billion wild birds and 6.9±20.7 billion mammals
every year (most of the mammals are native wild
than from automobile
mammals like shrews, chipmunks and voles, instead
strikes, pesticides and
of introduced pests like the Norway rat), plus
poisons, collisions with
numerous reptiles. In California areas with feral
skyscrapers and windmills,
cats, housemice (an invasive species) were more
and other causes.
Source: Loss, S.R. et al. 2013. The impact
abundant (more likely to survive) than native
of free ranging cats on wildlife of the United
rodents. Feral cats also pose a threat to poultry
States: Nature Communications.
producers (chicken farms),and even to other cats.
Recent studies estimate that free-roaming pets account for only about 29% of the birds and
11% of the mammals killed by domestic cats each year, and the real problem arises over how
to manage the 80 million or so stray or feral cats that commit the bulk of the wildlife slaughter.
Economic and Other Impacts
Ecologists estimate that predation of birds by cats has an economic impact of over $17
billion per year in the United States. Free-roaming cats account for the most cases of
human rabies exposure among domestic animals, and are the source for at least one-third
of rabies post-exposure treatments in the US: this is another significant economic impact.
Humane societies estimate that the cost imposed on U.S. taxpayers each year to impound,
shelter, euthanize, and dispose of homeless animals (including cats and other animals) is
$2 billion.
Looking at the issue from humane societies provides a more personal perspective. Each
day, about 70,000 puppies and kittens are born in the United States. (In contrast, 10,000
humans are born in the United States each day; there will never be enough homes for
animals with animal birth rates so high). In 2012, six to eight million cats and dogs were
taken to animal shelters in the US, and 2.8 million were euthanized.
Sources:
 Fenwick, G. 2013. House cats: The destructive invasive species purring on your lap: Baltimore Sun, February 25, 2013.
Online at http://articles.baltimoresun.com/2013-02-25/news/bs-ed-cats-20130225_1_outdoor-cats-house-cats-rabiesexposure
 Hildreth, A.M., et al. 2010. Feral Cats and Their Management. University of Nebraska, Lincoln Extension. Online at
http://www.ianrpubs.unl.edu/epublic/live/ec1781/build/ec1781.pdf
 Loss, S.R. et al. 2013. The impact of free ranging cats on wildlife of the United States: Nature Communications. Online
at http://www.nature.com/ncomms/journal/v4/n1/full/ncomms2380.html
 Felis catus, mammal, in Global Invasive Species Database. (Invasive Species Specialist Group of the IUCN Species
Survival Commission). Online at (GISP)http://www.issg.org/database/species/ecology.asp?si=24
 The Humane Society of the United States. 2012. Online at
http://www.humanesociety.org/issues/pet_overpopulation/facts/pet_ownership_statistics.html
Numbers of mammals, birds, and reptiles brought home by cats that did not
Numbers
of mammals,
birds,
reptiles
brought
home by
cats that did not
wear
bells
columns)
andand
that
did- Interdependent
wear
bells (black
columns).
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in Ecosystems- 2014.2015
wear bells (white columns) and that did wear bells (black columns).
The Domestic Cat: Felis catus
Reptiles
Numbers of mammals, birds, and reptiles brought home by cats that
were not allowed outdoors at nights (white columns) and that were
allowed out at nights (black columns).
Reptiles
Sources of both graphs:
 Woods, M. et al. 2013. Domestic Cat Predation on Wildlife: The Mammal Society. Online at
http://www.mammal.org.uk/sites/default/files/Domestic%20Cat%20Predation%20on%20Wildlife.pdf
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The Domestic Cat: Felis catus
What is the best control plan?
Since cats are revered as pets in our society, this
raises the moral dilemma of how to handle them when
they have become a threat to native wildlife. Animal
rights activists argue that many control methods,
especially euthanization of feral or domesticated cats,
are unethical. Some animal welfare groups feed feral
cats, while PETA recommends trapping, neutering,
and adopting feral cats. Wildlife organizations argue
that cat predation of wildlife is serious, and that
humans sheltering and feeding cats is directly
responsible for the cat population reaching a density
one hundred times greater than the populations of
their native counterparts. Public health specialists
argue that feral cats are responsible for the
transmission of serious diseases. Humane societies
work hard to educate the public about the impact of
an exploding cat population, but the problem remains.
Obviously there are two quite different situations for management of the species,
depending on the status of the cat: one is where a cat is a domesticated household pet, and
the other is when a cat has gone wild or feral and has no owner to protect and feed it. Both
situations involve different stakeholders, and different solutions. To further complicate the
issue, in many states, since feral cats are not classified as wildlife, responsibility for
management of the cat populations is unclear.
Different communities, states,
and nations have approached
the cat issue with a variety of
species management tactics,
from habitat modification,
fencing, repellants, trapping,
fertility control, and finding
foster homes, to euthanization
and hunting.
The BP Deepwater Horizon oil spill,
widely considered to be the worst
environmental disaster in the history of
the United States, resulted in the deaths
of over 7,000 birds:
A 2009 study estimated the number of
birds killed by cats every year in the
United States at one billion,
conservatively.
Sources:
 Ecological Impacts of Feral Cats. 2011. The Wildlife Society. Online at
http://joomla.wildlife.org/documents/cats_ecological_impacts.pdf
 Hildreth, A.M., et al. 2010. Feral Cats and Their Management. University of Nebraska, Lincoln Extension. Online at
http://www.ianrpubs.unl.edu/epublic/live/ec1781/build/ec1781.pdf
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The Domestic Cat: Felis catus
On the prowl: In suburban backyards and rural fields, free-roaming cats are
pouncing on songbird populations.
John S. Coleman and Stanley A. Temple
Some days, you need a bit of imagination to view a house cat as a predator. Sitting in a
sunny window, or curled up on a bed, most tabbies hardly seem to have the energy to
attack their food dish. But cats are definitely hunters, and there are plenty of them in town,
in barns and free-ranging in fields to put the bite on a variety of birds and other wildlife.
Cat populations are tough to estimate accurately. U.S. Census data track cats that people
claim to own as pets, and the numbers are impressive. From 1970 to 1990, the number of
urban and rural cats counted in the census rose from 30 million to 60 million. Nationwide,
approximately 30% of households ‘own’ cats. In rural areas, where free-roaming cats often
are not regarded as pets, and not recorded by the census, as many as 60% of households
keep cats on their property. Nationwide, there must be at least 100 million cats.
Wild at heart
Although cats make affectionate pets, their skills and behaviors as predators remain unchanged from those of their ancestors, and they hunt as effectively as their wild forebears.
However, house cats differ from wild predators in several important ways: First, people
protect cats from disease, predation and competition. Modern veterinary practices, from
vaccination to bone setting, substantially extend a pet cat's lifespan. Second, domestic cats
adapt well to human domiciles. Unlike native predators, cat densities are not limited by
space or the availability of prey. Even barn cats have significantly better shelter, food and
water supplies than bobcats, foxes and coyotes. The cat's range extends every time people
build new homes and outside shelters. Third, although most people supply their cats with
food, research shows feeding does not suppress the cat's instinct to hunt and kill.
These factors combine to make free-ranging cats a potent predatory force, especially in
rural areas. We've estimated that in some parts of rural Wisconsin, cat densities reach 114
animals per square mile – much higher than all mid-sized native predators. Given ample
food supplies and high reproductive rates, cat densities can exceed nine animals per acre.
Rural cats have access to many animals and have the greatest impact. Small mammals like
mice and voles make up about 70 percent of their diets, birds constitute about 20, and a
mix of other animals constitute the remaining 10%. Research in Wisconsin suggests that
free-ranging rural cats may be killing 219 million birds in the state; many are native songbirds whose populations are already stressed by factors including development, habitat
destruction and pesticide pollution. Many of these birds are ground-nesting birds, like
meadowlarks and sparrows, or birds that often feed on the ground, like robins.
Cat predation affects wildlife dynamics in other ways. Domestic cats eat many of the same
animals that native predators eat. Studies show that large numbers of cats reduce available
prey for predators, such as hawks and weasels.
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The Domestic Cat: Felis catus
Free-ranging cats may also transmit diseases to wild animals. Domestic cats have spread
feline leukemia virus to mountain lions, and may recently have infected the endangered
Florida Panther with feline distemper (feline panleucopenia). Unvaccinated cats can also
transmit rabies and toxoplasmosis to people. Pregnant women are now routinely advised to
avoid contact with cats and litter boxes to minimize the risk of infection.
Suggestions for keeping cats in check
1. If you are going to keep cats and you don't intend to breed them, get them neutered at
about six months of age.
2. Don't dispose of unwanted cats by releasing them in rural areas.
3. If possible and practical, keep your cat indoors.
4. Research shows bells on cat collars are mostly ineffective in preventing predation.
5. Declawing may reduce hunting success, but declawed cats are still effective predators.
6. Locate bird feeders in sites that don't provide cover for cats.
7. Support community efforts to license and neuter domestic cats.
Estimating how many birds are killed by cats
 We estimate 1.4-2 million free-ranging cats in rural Wisconsin, and 23% of their diet
consists of birds. Other studies indicate 20-30% of free-ranging cat kills are birds.
 The number of animals killed by an individual cat varies greatly. One rural cat was
recorded to have killed 1,690 animals in an 18-month period. On an annual basis,
studies record low estimates of 14 animals per free-ranging urban cat to at least one
animal per day for rural cats. Other studies reported 28 kills per year for urban cats,
and 91 kills per year for rural cats.
Here are our best guesses at low, intermediate, and high estimates of the number of birds
killed annually by rural cats in Wisconsin, based on the formula*:
(number of rural cats) x (number of kills/cat/year) x (% of kills that are birds).
Low value:
(lowest population estimate) x (twice kill rate by urban cats) x (low percentage of kills that are birds)
1.4 million cats x 28 x 20% = 7.8 million birds killed by rural cats
Intermediate value:
(mean population estimate) x (intermediate kill rate) x (higher percentage of kills that are birds)
1.7 million cats x 91 x 25% = 38.7 million birds killed by rural cats
High value:
(highest population estimate) x (highest kill rate) x (highest percentage of kills that are birds)
2 million cats x 365 x 30% = 219 million birds killed by rural cats
*Note: these estimates do not include predation by urban cats.
Adapted from:
 Coleman, J.S. and Temple, S.A. 1996. On the prowl: In suburban backyards and rural fields, free-roaming cats are
pouncing on songbird populations. Wisconsin Natural Resources. Online at
http://dnr.wi.gov/wnrmag/html/stories/1996/dec96/cats.htm
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The Domestic Cat: Felis catus
Harmful Parasites In Cat Poop Are Widespread
ANNA HAENSCH
July 09, 2013 5:07 PM ET
Playgrounds and sandboxes are popular
hangouts for free-roaming cats. What they leave
behind may not be so popular with humans.
That cat poop can pose a health risk to humans no
longer surprises us. Some cats carry a parasite
called Toxoplasma gondii. Infected cats shed
embryonic T. gondii, called oocysts, in their feces.
These oocysts are easily transmitted to humans,
and researchers have explored their possible link
Photo by Alan Turkus/Flickr
to various mental health problems, including
schizophrenia. More recently, studies of schoolage children show a correlation between testing positive for T. gondii and having difficulty
in school.
The parasites can cause more acute health problems in newborns and people with weak
immune systems, as the Centers for Disease Control and Prevention points out. A report
published in Trends in Parasitology explores how substantial a public health threat the
parasite poses in the United States. One thing's pretty clear: There are a lot of oocysts out
there.
Research psychiatrist Dr. E. Fuller Torrey and pediatric infectious disease specialist Dr.
Robert Yolken, who have spent years investigating the role that animals play in the spread
of infectious diseases, co-authored the roundup. Shots spoke with Torrey, who says there
are four factors that he believes makes this a valid health concern:
 The cat population is growing.
 Every day about 1 million cats in the U.S. are actively pooping out as many as 50
millionoocysts apiece.
 The oocycts are hard to kill.
 There is a well-documented correlation between mental illness and testing positive
for T. gondii antibodies.
"This is a public health problem that bears more scrutiny," Torrey says. "We're walking a
tight line between alarming people and failing to point out obvious health problems that
need to be paid attention to."
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The Domestic Cat: Felis catus
Correlation isn't the same as causation, however, particularly when it comes to the area of
mental health. "The association has been discussed, but it has not been completely
accepted by everyone," Dr. William Schaffner, chairman of the department of preventive
medicine at Vanderbilt University, told NBC News. "If people were convinced of that, we
would have acted on it."
Sneaky Parasite Attracts Rats to Cats
Katie Lisnik, who is the director of Cat Protection and Policy at the Humane Society, says
there are 86 million cats that are household pets in the United States, and another 20 million
to 80 million free-roaming cats.
The bulk of oocysts are getting dropped in the very places where humans are most active.
"Feral cats tend to be where the people are, and it makes sense," Lisnik says. "They want to
be around us, and we're their source of food." The presence of large numbers of oocysts
on playgrounds and in sandboxes, where kids stick their hands in their mouths every
couple of minutes, bears particular attention, Torrey says. "If you have a sandbox that isn't
covered, get rid of the sand and cover it when kids aren't playing," he says.
He also has advice for green thumbs. "Studies have shown that you can have almost 100
oocysts under your fingernails after gardening. So always wash your hands after
gardening, and wash vegetables before eating them," he says.
In case you're afraid of what this means for your own pet, Torrey says, "strictly indoor cats
really shouldn't be a problem. The chance of them becoming infected is very low."
Torrey also says that while there has been a drastic increase in the number of feral cats,
there has been a decrease in the number of recorded cases of T. gondii infection. The
public, he says, is more aware of the dangers of eating improperly stored meat, a source of
infections.
But Torrey also points out that T. gondii can sit dormant in the body for 20 years, so it may
actually take a few decades to see the epidemiological effects on humans.
Source:
Haensch, A. 2013. Harmful Parasites in Cat Poop are Widespread. National Public Radio. Online at
http://www.npr.org/blogs/health/2013/07/05/199041322/harmful-parasites-in-cat-poop-are-widespread
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