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Anthropogenic threats, such as collisions with man-made structures, vehicles, poisoning and predation by domestic pets, combine to kill billions of wildlife annually. Free-ranging domestic cats have been introduced globally and have contributed to multiple wildlife extinctions on islands. The magnitude of mortality they cause in mainland areas remains speculative, with large-scale estimates based on non-systematic analyses and little consideration of scientific data. Here we conduct a systematic review and quantitatively estimate mortality caused by cats in the United States. We estimate that free-ranging domestic cats kill 1.4-3.7 billion birds and 6.9-20.7 billion mammals annually. Un-owned cats, as opposed to owned pets, cause the majority of this mortality. Our findings suggest that free-ranging cats cause substantially greater wildlife mortality than previously thought and are likely the single greatest source of anthropogenic mortality for US birds and mammals. Scientifically sound conservation and policy intervention is needed to reduce this impact.
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Received 6 Sep 2012 |Accepted 12 Dec 2012 |Published 29 Jan 2013
The impact of free-ranging domestic cats
on wildlife of the United States
Scott R. Loss1, Tom Will2& Peter P. Marra1
Anthropogenic threats, such as collisions with man-made structures, vehicles, poisoning and
predation by domestic pets, combine to kill billions of wildlife annually. Free-ranging domestic
cats have been introduced globally and have contributed to multiple wildlife extinctions on
islands. The magnitude of mortality they cause in mainland areas remains speculative, with
large-scale estimates based on non-systematic analyses and little consideration of scientific
data. Here we conduct a systematic review and quantitatively estimate mortality caused by
cats in the United States. We estimate that free-ranging domestic cats kill 1.3–4.0 billion birds
and 6.3–22.3 billion mammals annually. Un-owned cats, as opposed to owned pets, cause the
majority of this mortality. Our findings suggest that free-ranging cats cause substantially
greater wildlife mortality than previously thought and are likely the single greatest source of
anthropogenic mortality for US birds and mammals. Scientifically sound conservation and
policy intervention is needed to reduce this impact.
DOI: 10.1038/ncomms2380
1Migratory Bird Center, Smithsonian Conservation Biology Institute, National Zoological Park, P.O. Box 37012 MRC 5503, Washington, District of Columbia
20013, USA. 2U.S. Fish and Wildlife Service, Division of Migratory Birds, Midwest Regional Office, 3815 American Boulevard East, Bloomington, Minnesota
20013, USA. Correspondence and requests for materials should be addressed to S.R.L. (email:
NATURE COMMUNICATIONS | 4:1396 | DOI: 10.1038/ncomms2380 | 1
&2013 Macmillan Publishers Limited. All rights reserved.
Domestic cats (Felis catus) are predators that humans have
introduced globally1,2 and that have been listed among
the 100 worst non-native invasive species in the world3.
Free-ranging cats on islands have caused or contributed to 33
(14%) of the modern bird, mammal and reptile extinctions
recorded by the International Union for Conservation of Nature
(IUCN) Red List4. Mounting evidence from three continents
indicates that cats can also locally reduce mainland bird and
mammal populations5–7 and cause a substantial proportion
of total wildlife mortality8–10. Despite these harmful effects,
policies for management of free-ranging cat populations and
regulation of pet ownership behaviours are dictated by animal
welfare issues rather than ecological impacts11. Projects to
manage free-ranging cats, such as Trap-Neuter-Return (TNR)
colonies, are potentially harmful to wildlife populations, but
are implemented across the United States without widespread
public knowledge, consideration of scientific evidence or the
environmental review processes typically required for actions
with harmful environmental consequences11,12.
A major reason for the current non-scientific approach to
management of free-ranging cats is that total mortality from cat
predation is often argued to be negligible compared with other
anthropogenic threats, such as collisions with man-made
structures and habitat destruction. However, assessing the
conservation importance of a mortality source requires identifica-
tion of which species are being killed (for example, native versus
non-native invasive species and rare versus common species) in
addition to estimation of total numbers of fatalities. Estimates of
annual US bird mortality from predation by all cats, including
both owned and un-owned cats, are in the hundreds of
millions13,14 (we define un-owned cats to include farm/barn
cats, strays that are fed by humans but not granted access to
habitations, cats in subsidized colonies and cats that are
completely feral). This magnitude would place cats among the
top sources of anthropogenic bird mortality; however, window
and building collisions have been suggested to cause even greater
mortality15–17. Existing estimates of mortality from cat predation
are speculative and not based on scientific data13–16 or, at best,
are based on extrapolation of results from a single study18.In
addition, no large-scale mortality estimates exist for mammals,
which form a substantial component of cat diets.
We conducted a data-driven systematic review of studies that
estimate predation rates of owned and un-owned cats, and
estimated the magnitude of bird and mammal mortality caused
by all cats across the contiguous United States (all states excluding
Alaska and Hawaii). We estimate that free-ranging domestic cats
kill 1.3–4.0 billion birds and 6.3–22.3 billion mammals annually,
and that un-owned cats cause the majority of this mortality. This
magnitude of mortality is far greater than previous estimates of
cat predation on wildlife and may exceed all other sources of
anthropogenic mortality of US birds and mammals.
The magnitude of bird mortality caused by cat predation. After
excluding studies that did not meet a priori inclusion criteria
designed to increase the accuracy of our analysis, we developed
probability distributions of predation rates on birds and mam-
mals. We combined predation rate distributions with literature-
derived probability distributions for US cat population sizes, and
we also accounted for the proportion of owned cats allowed
outdoors, the proportion of owned and un-owned cats that hunt,
and imperfect detection of owned cats’ prey items.
We generated an estimated range of bird and mammal mor-
tality caused by cat predation by incorporating the above
distributions—including separate predation rate distributions for
owned and un-owned cats—and running 10,000 calculation
iterations. We augmented US predation data by incorporating
predation rate estimates from other temperate regions
(Supplementary Table S1). For birds, we generated three US
mortality estimates based on predation data from studies in:
(1) the United States, (2) the United States and Europe and
(3) the United States, Europe, and other temperate regions (pri-
marily Australia and New Zealand). Owing to a lack of US studies
of un-owned cat predation on mammals, we estimated mammal
mortality using data groupings 2 and 3. We based all other
probability distributions on US studies (distribution details in
Table 1; data in Supplementary Table S2).
The three estimates of bird mortality varied moderately, with a
19% difference among median estimates (Table 2). We focus
interpretation on the estimate generated using US and European
predation data because it is the lowest value. Furthermore, this
estimate is more likely to be representative of the US than the
estimate based on incorporation of data from Australia and New
Zealand, where the wildlife fauna and climate are less similar
to the United States. We estimate that cats in the contiguous
United States annually kill between 1.3 and 4.0 billion birds
(median ¼2.4 billion) (Fig. 1a), with B69% of this mortality
caused by un-owned cats. The predation estimate for un-owned
cats was higher primarily due to predation rates by this group
averaging three times greater than rates for owned cats.
The magnitude of mammal mortality caused by cat predation.
Our estimate of mammal mortality was robust to the choice of
predation data as evidenced by a 1.6% difference between the two
median estimates (Table 2). We focus interpretation on the lower
estimate, which was based on United States and European pre-
dation data and US values of other parameters. We estimate
annual mammal mortality in the contiguous United States at
between 6.3 and 22.3 billion (median ¼12.3 billion) (Fig. 1b) with
89% of this mortality caused by un-owned cats. The estimate that
incorporated European data (but not data from Australia and
New Zealand) may be slightly lower because wildlife across much
of Europe were historically exposed to predation by a similarly-
sized wild cat (Felis sylvestris) and, therefore, may be less naive to
predation by domestic cats. However, it is unlikely that European
wildlife have fully adapted to the unusually high densities of
domestic cats in much of this continent9.
Factors explaining estimate uncertainty. For both birds and
mammals, sensitivity analyses indicated that un-owned cat
parameters explained the greatest variation in total mortality
estimates (Fig. 2). Un-owned cat population size explained the
greatest variation in mortality estimates (42% for birds and 51%
for mammals), and the un-owned cat predation rate explained the
second greatest variation (24% for birds and 40% for mammals).
The only other parameters that explained 45% of variation in
mortality estimates were the owned cat predation rate on birds
(16%) and the correction factor for imperfect detection of owned
cats’ prey items (8%).
Our estimate of bird mortality far exceeds any previously
estimated US figure for cats13,14,16, as well as estimates for any
other direct source of anthropogenic mortality, including
collisions with windows, buildings, communication towers,
vehicles and pesticide poisoning13,15–21. Systematic reviews like
ours, which includes protocol formulation, a data search strategy,
data inclusion criteria, data extraction and formal quantitative
analyses22, are scarce for other anthropogenic mortality sources.21
Increased rigour of mortality estimates should be a high priority
2NATURE COMMUNICATIONS | 4:1396 | DOI: 10.1038/ncomms2380 |
&2013 Macmillan Publishers Limited. All rights reserved.
Table 2 | Median estimates of annual wildlife mortality caused by cat predation in the contiguous United States.
Predation data used Mortality estimate (millions)
Owned cats Un-owned cats Total
Bird US 1,053 (104–3,039)* 1,792 (861–3,276) 2,967 (1,358–5,324)
US and Europe 684 (221–1,682)w1,652 (803–2,955)2,407 (1,306–3,992)
All temperate 508 (172–1,226) 1,876 (983–3,124) 2,437 (1,378–3,814)
Mammal US and Europe 1,249 (512–2,862)10,903 (4,991–20,874)12,269 (6,259–22,257)
All temperate 958 (397–2,117) 11,426 (5,874–19,451) 12,473 (6,874–20,421)
Both Taxa 1,933 (733–4,544) 12,555 (5,794–23,829) 14,676 (7,565–26,249)
*Values in parentheses indicate central 95% of estimates.
wBold face indicates estimates from which inference is drawn in the text.
Table 1 | Probability distributions used for parameters in cat predation model.
Parameter Number of studies used* Distribution type Distribution parameters
Owned cats
Number of owned cats in contiguous United States 2 Normal Mean ¼84 M, s.d. ¼2.5 M
Proportion of owned cats with outdoor access 8 Uniform Min ¼0.4, max ¼0.7
Proportion of outdoor owned cats that hunt 3 Uniform Min ¼0.5, max ¼0.8
Correction for owned cats not returning prey 3 Uniform Min ¼1.2, max ¼3.3
BIRD return rate per cat per year
US studies 4 Uniform Min ¼1.0, max ¼34.1
US and Europe studies 11 Uniform Min ¼4.2, max ¼18.3
All temperate studies 17 Uniform Min ¼3.4, max ¼13.2
MAMMAL return rate per cat per year
US studies 1 NAwNA
US and Europe studies 7 Uniform Min ¼11.1, max ¼29.5
All temperate studies 13 Uniform Min¼8.7, max ¼21.8
REPTILE return rate per cat per year
US studies 0 NA NA
US and Europe studies 1 NA NA
All temperate studies 8 Uniform Min ¼0.4, max ¼2.21
AMPHIBIAN return rate per cat per year
US studies 0 NA NA
US and Europe studies 1 NA NA
All temperate studies 5 Uniform Min ¼0.05, max ¼0.5
Un-owned cats
Number of un-owned cats in contiguous United States 5 Uniform Min ¼30 M, max ¼80 M
Proportion of un-owned cats that hunt 2 Uniform Min ¼0.8, max ¼1.0
BIRD predation rate per cat per year
US studies 8 Uniform Min ¼24.4, max ¼51.4
US and Europe studies 11 Uniform Min ¼23.2, max ¼46.2
All temperate studies 19 Uniform Min ¼30.0, max ¼47.6
MAMMAL predation rate per cat per year
US studies 6 Uniform Min ¼162.3, max ¼354.9
US and Europe studies 7 Uniform Min ¼139.4, max ¼328.6
All temperate studies 13 Uniform Min ¼177.3, max ¼299.5
REPTILE predation rate per cat per year
US studies 1 NA NA
US and Europe studies 2 NA NA
All temperate studies 10 Uniform Min ¼4.2, max ¼12.4
AMPHIBIAN predation rate per cat per year
US studies 0 NA NA
US and Europe studies 0 NA NA
All temperate studies 3 Uniform Min ¼1.9, max ¼4.7
*Number of studies found that include an estimate of the model parameter.
wNo calculation was conducted for this data grouping because of limited data.
NATURE COMMUNICATIONS | 4:1396 | DOI: 10.1038/ncomms2380 | 3
&2013 Macmillan Publishers Limited. All rights reserved.
and will allow increased comparability of mortality sources23.
Nonetheless, no estimates of any other anthropogenic mortality
source approach the value we calculated for cat predation, and
our estimate is the first for cats to be based on rigorous data-
driven methods. Notably, we excluded high local predation rates
and used assumptions that led to minimum predation rate
estimates for un-owned cats; therefore, actual numbers of birds
killed may be even greater than our estimates.
Free-roaming cats in the United States may also have a
substantial impact on reptiles and amphibians. However, US
studies of cat predation on these taxa are scarce. To generate a
first approximation of US predation rates on reptiles and
amphibians, we used the same model of cat predation along
with estimates of cat predation rates on these taxa from studies in
Europe, Australia and New Zealand. We estimate that between
228 to 871 million reptiles (median ¼478 million) and between
86 and 320 million amphibians (median ¼173 million) could be
killed by cats in the contiguous United States each year. Reptile
and amphibian populations, and, therefore, cat predation rates,
may differ between the regions where we gathered predation data
for these taxa and the United States. Furthermore, reptiles and
amphibians are unavailable as prey during winter across much of
the United States. Additional research is needed to clarify impacts
of cats on US herpetofauna, especially given numerous anthro-
pogenic stressors that threaten their populations (for example,
climate change, habitat loss and infectious diseases) and
documented extinctions of reptiles and amphibians due to cat
predation in other regions4,24.
The exceptionally high estimate of mammal mortality from cat
predation is supported by individual US studies that illustrate
high annual predation rates by individual un-owned cats in excess
of 200 mammals per year6,25–28 and the consistent finding that
cats preferentially depredate mammals over other taxa
(Supplementary Table S1). Even with a lower yearly predation
rate of 100 mammals per cat, annual mortality would range from
3–8 billion mammals just for un-owned cats, based on a
population estimate of between 30 and 80 million un-owned
cats. This estimated level of mortality could exceed any other
direct source of anthropogenic mortality for small mammals;
however, we are unaware of studies that have systematically
quantified direct anthropogenic mortality of small terrestrial
mammals across large scales.
Native species make up the majority of the birds preyed upon
by cats. On average, only 33% of bird prey items identified to
species were non-native species in 10 studies with 438 specimens
of 58 species (Supplementary Table S3). For mammals, patterns
of predation on native and non-native species are less clear and
appear to vary by landscape type. In densely populated urban
areas where native small mammals are less common, non-native
species of rats and mice can make up a substantial component of
mammalian prey29. However, studies of mammals in suburban
and rural areas found that 75–100% of mammalian prey were
native mice, shrews, voles, squirrels and rabbits26,30,31. Further
research of mammals is needed to clarify patterns of predation by
both owned and un-owned cats on native and non-native
mammals, and across different landscape types.
Sensitivity analyses indicate that additional research of
un-owned cats will continue to improve precision of mortality
estimates. Our finding that un-owned cat population size and
Median= 2.4 billion
Estimate frequency
Estimate frequency
0 1,000 2,000 3,000 4,000 5,000
05,000 10,000 15,000
Mortality (millions)
20,000 25,000
Median= 12.3 billion
Figure 1 | Estimates of cat predation on US birds and mammals.
(a) Probability distribution of estimated bird mortality caused by all free-
ranging cats in mainland areas of the contiguous United States.
(b) Probability distribution of estimated mammal mortality caused by all
free-ranging cats in mainland areas of the contiguous United States.
Number of owned pet cats
Proportion of pet cats outdoors
Proportion of outdoor pet cats
Outdoor pet cat predation rate
Detectability correction for pet
cat prey items
Number of un-owned cats
Proportion of un-owned cats
Un-owned cat predation rate
0 % 10 % 20 % 30% 40 % 50 % 60%
Figure 2 | Factors explaining uncertainty in estimates of wildlife mortality from cat predation. Amount of variation in estimates of wildlife mortality in
the contiguous United States contributed by each parameter in the cat predation model (percentages represent adjusted R2values from multiple regression
4NATURE COMMUNICATIONS | 4:1396 | DOI: 10.1038/ncomms2380 |
&2013 Macmillan Publishers Limited. All rights reserved.
predation rate explained the greatest variation in mortality
estimates reflects the current lack of knowledge about un-owned
cats. No precise estimate of the un-owned cat population exists
for the United States because obtaining such an estimate is cost
prohibitive, and feral un-owned cats are wary of humans and tend
to be solitary outside of urban areas. In addition, human
subsidized colonies of un-owned cats are maintained without
widespread public knowledge. For example, in Washington DC
alone there are 4300 managed colonies of un-owned cats and an
unknown number of unmanaged colonies. Population size
estimates can be improved by incorporating observations of
free-ranging cats into a wildlife mortality reporting database23.
Context for the population impact of a mortality source depends
on comparing mortality estimates to estimates of population
abundance of individual species. However, continental-scale
estimates of wildlife population abundance are uncertain due to
spatio-temporal variation in numbers. For mammals, clarification
of the population impacts of cat predation is hindered by the
absence of nationwide population estimates. For all North
American land birds, the group of species most susceptible to
mainland cat predation (Supplementary Table S3), existing
estimates range from 10–20 billion individuals in North
America32. A lack of detail about relative proportions of
different bird species killed by cats and spatio-temporal variation
of these proportions makes it difficult to identify the species and
populations that are most vulnerable. The magnitude of our
mortality estimates suggest that cats are likely causing population
declines for some species and in some regions. Threatened and
endangered wildlife species on islands are most susceptible to the
effects of cat predation, and this may also be true for vulnerable
species in localized mainland areas5because small numbers of
fatalities could cause significant population declines. Threatened
species in close proximity to cat colonies—including managed
TNR colonies11,12—face an especially high level of risk; therefore,
cat colonies in such locations comprise a wildlife management
priority. Claims that TNR colonies are effective in reducing cat
populations, and, therefore, wildlife mortality, are not supported
by peer-reviewed scientific studies11.
Our estimates should alert policy makers and the general
public about the large magnitude of wildlife mortality caused by
free-ranging cats. Structured decisions about actions to reduce
wildlife mortality require a quantitative evidence base. We
provide evidence of large-scale cat predation impacts based on
systematic analysis of multiple data sources. Future specific
management decisions, both in the United States and globally,
must be further informed by fine scale research that allows
analysis of population responses to cats and assessment of the
success of particular management actions. We are not suggesting
that other anthropogenic threats that kill fewer individuals are
biologically unimportant. Virtually nothing is known about the
cumulative population impacts of multiple mortality sources.
Furthermore, comparison of total mortality numbers has limited
use for prioritization of risks and development of conservation
objectives. Combining per species estimates of mortality with
population size estimates will provide the greatest information
about the risk of population-level impacts of cat predation.
Although our results suggest that owned cats have relatively less
impact than un-owned cats, owned cats still cause substantial
wildlife mortality (Table 2); simple solutions to reduce mortality
caused by pets, such as limiting or preventing outdoor access,
should be pursued. Efforts to better quantify and minimize
mortality from all anthropogenic threats are needed to increase
sustainability of wildlife populations.
The magnitude of wildlife mortality caused by cats that we
report here far exceeds all prior estimates. Available evidence
suggests that mortality from cat predation is likely to be
substantial in all parts of the world where free-ranging cats
occur. This mortality is of particular concern within the context
of steadily increasing populations of owned cats, the potential for
increasing populations of un-owned cats12, and an increasing
abundance of direct and indirect mortality sources that threaten
wildlife in the United States and globally.
Literature search. We searched JSTOR, Google Scholar, and the Web of Science
database (formerly ISI Web of Science) within the Web of Knowledge search
engine published by Thomson Reuters to identify studies that document cat pre-
dation on birds and mammals. We initially focused this search on US studies, but
due to a limited sample of these studies, we expanded the search to include pre-
dation research from other temperate regions. We also searched for studies pro-
viding estimates of cat population sizes at the scale of the contiguous United States
and for US studies that estimate the proportion of owned cats with outdoor access
and the proportion of cats that hunt wildlife. The search terms we used included:
‘domestic cat’ in combination with ‘predation,’ ‘prey,’ ‘diet,’ ‘food item’ and
‘mortality’; all previous terms with ‘domestic cat’ replaced by ‘Felis catus,’ ‘feral,’
‘stray,’ ‘farm,’ ‘free-ranging,’ and ‘pet’; ‘trap-neuter-return colony’; ‘TNR colony’;
and ‘cat predation’ in combination with ‘wildlife,’ ‘bird,’ ‘mammal,’ and ‘rodent’.
We checked reference lists of articles to identify additional relevant studies. Lead
authors of three studies were also contacted to enquire whether they knew of
ongoing or completed unpublished studies of cat predation in the United States.
Classification of cat ranging behaviour. We grouped studies based on the ran-
ging behaviour of cats investigated. We defined owned cats to include owned cats in
both rural and urban areas that spend at least some time indoors and are also
granted outdoor access. We defined un-owned cats to include all un-owned cats
that spend all of their time outdoors. The un-owned cat group includes semi-feral
cats that are sometimes considered pets (for example, farm/barn cats and strays
that are fed by humans but not granted access to habitations), cats in subsidized
(including TNR) colonies, and cats that are completely feral (that is, completely
independent and rarely interacting with humans). We did not classify cats by
landscape type or whether they receive food from humans because the amount of
time cats spend outdoors is a major determinant of predation rates33,34 and
because predation is independent of whether cats are fed by humans6,34,35.
Study inclusion criteria. Studies were only included if: (1) they clearly reported cat
ranging behaviour (that is, a description of whether cats were owned or un-owned
and whether they were outdoor cats or indoor-outdoor cats), and (2) the group of
cats investigated fit exclusively into one of the two groups we defined above (that is,
we excluded studies that lumped owned and un-owned cats in a single predation
rate estimate). For some studies, we extracted a portion of data that met these
criteria but excluded other data from cats with unknown ranging behaviour. We
only included mainland and large island (New Zealand and United Kingdom)
predation studies, because cat predation on small islands is often exceptionally
high36,37 and focused on colony nesting seabirds38. We excluded studies from
outside temperate regions and those with predation rate estimates based on fewer
than 10 cats, o1 month of sampling, or on cats that were experimentally
manipulated (for example, by fitting them with bells or behaviour altering bibs).
We included studies that used cat owners’ records of prey returns, but we excluded
those that asked owners to estimate past prey returns because such questionnaires
may lead to bias in estimation of predation rates39. (For a list of all included and
excluded studies, see Supplementary Table S1).
Data extraction and standardization of predation rates. Most studies report an
estimate of cat predation rate (that is, daily, monthly or annual prey killed per cat)
or present data that allowed us to calculate this rate. When studies only reported
predation rate estimates for all wildlife combined, we calculated separate predation
rates by extracting taxa-specific prey counts from tables or figures and multiplying
the total predation rate by the proportion of prey items in each taxon. If taxa-
specific counts were not provided, we directly contacted authors to obtain this
information. For studies that presented low, medium and high estimates or low and
high estimates, we used the medium and average values, respectively. For studies
that presented more than one predation estimate for cats with similar ranging
behaviour (for example, owned cats in rural and urban areas), we calculated the
average predation rate.
Nearly all studies of un-owned cats report numbers or frequencies of occurrence
of different taxa in stomachs and/or scats. For studies reporting numbers of prey
items, we estimated annual predation rates by assuming one stomach or scat
sample represented a cat’s average daily prey intake (for example, an average of one
prey item per stomach or scat ¼365 prey per cat per year). This assumption likely
resulted in conservative estimates because cats generally digest prey within 12 h
(ref. 28) and can produce two or more scats each day29. For studies reporting
occurrence frequencies of prey items, we assumed this proportion represented a
cat’s average daily prey intake (for example, a 10% bird occurrence rate ¼0.1 bird
NATURE COMMUNICATIONS | 4:1396 | DOI: 10.1038/ncomms2380 | 5
&2013 Macmillan Publishers Limited. All rights reserved.
per stomach or scat ¼36.5 birds per cat per year). This assumption results in coarse
predation rate estimates, but estimates from this approach are even more
conservative than those from the first assumption because many stomachs and
scats undoubtedly included more than one bird or mammal.
Predation rate estimates from many studies were based on continuous year-
round sampling or multiple sampling occasions covering all seasons. However,
seasonal coverage of some studies was incomplete. To generate full-year predation
rate estimates in these cases, we adjusted partial-year predation estimates according
to the average proportion of prey taken in each month as determined from year-
round studies reporting monthly data (birds and mammals8,33, birds only7,40). For
partial-year estimates from the northern hemisphere, we offset monthly estimates
from southern hemisphere studies by 6 months. The final annual predation rate
estimates for all studies are presented in Supplementary Table S1. The year-round
studies we used represent different geographical regions (for birds—England,
Kansas (US), Australia and New Zealand; for mammals—England and Australia)
with varying climates and slightly varying seasonal patterns of predation. For both
birds and mammals, averaging across full-year studies resulted in higher
proportions of predation in the spring and summer compared with fall and winter,
an expected pattern for much of the United States. The reference studies we used,
therefore, provide a reasonable baseline for correcting to full-year mortality
estimates. This approach greatly improves upon the assumption that mortality is
negligible during the period of the year not covered by sampling.
Quantification of annual mortality from cat predation. We estimated wildlife
mortality in the contiguous United States by multiplying data-derived probability
distributions of predation rates by distributions of estimated cat abundance,
following41. Quantification was conducted separately for owned and un-owned cats
and for birds and mammals. As there was a relatively small sample of US studies
that estimated predation rates (n¼14 and 10 for birds and mammals, respectively),
we repeated calculations using predation rate distributions that were augmented
with predation rates from Europe and all temperate zones. However, we only used
studies from the contiguous United States to construct all other probability
distributions (listed below).
We estimated mortality using the following model of cat predation:
Annual mortality from owned cats mpðÞ¼npcpodpphpprcor ð1Þ
Annual mortality from unowned cats mfðÞ¼nfcpfhfpr ð2Þ
Total annual mortality from all cats ¼mp þmf ð3Þ
where npc is the number of owned cats in the contiguous United States, pod is the
proportion of owned cats granted outdoor access, pph is the proportion of outdoor
owned cats that hunt wildlife, ppr is the annual predation rate by owned cats, cor is
a correction factor to account for owned cats not returning all prey to owners, nfc
is the number of un-owned cats in the contiguous United States, pfh is the
proportion of un-owned cats that hunt wildlife, and fpr is the annual predation
rate by un-owned cats. From the probability distribution of each parameter
(see Table 1 and Supplementary Methods for details about the specific probability
distributions used), we randomly drew one value and used the above formulas to
calculate mortality. Random draws were made using distribution functions in
Programme R (rnorm and runif commands for normal and uniform distributions,
respectively). We conducted 10,000 random draws to estimate a potential
range of annual predation on each wildlife taxa. For all analyses, we report median
mortality estimates and lower and upper estimates bracketing the central 95% of
Sensitivity analyses. We used multiple linear regression analysis to assess how
much variance in mortality estimates was explained by the probability distribution
for each parameter. We treated total mortality estimates as the dependent variable
(n¼10,000) and we defined a predictor variable for each parameter that consisted
of the 10,000 randomly drawn values. We used adjusted R2values to interpret the
percentage of variance explained by each parameter.
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6NATURE COMMUNICATIONS | 4:1396 | DOI: 10.1038/ncomms2380 |
&2013 Macmillan Publishers Limited. All rights reserved.
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S.R.L. was supported by a postdoctoral fellowship funded by the US Fish and Wildlife
Service through the Smithsonian Conservation Biology Institute’s Postdoctoral Fellow-
ship programme. P. Blancher provided insight for development of the model of cat
predation magnitude, and R. Kays, C. Lepczyk and Y. van Heezik provided raw data from
their publications. C. Machtans facilitated data sharing, and participants in the 2011
Society of Canadian Ornithologists’ anthropogenic mortality of birds symposium pro-
vided context and perspectives. C. Lepczyk and P. Blancher provided comments on the
manuscript. The findings and conclusions in this article are those of the authors and do
not necessarily represent the views of the Smithsonian or US Fish and Wildlife Service.
All data used for this analysis is available in the Supplementary Materials.
Author contributions
S.R.L. designed the study, collected and analysed data, and wrote the paper. T.W. and
P.P.M. designed the study and contributed to paper revisions. All authors discussed the
results and commented on the manuscript.
Additional information
Supplementary Information accompanies this paper on
Competing financial interests: The authors claim no competing financial interests
associated with this paper.
Reprints and permission information is available online at
How to cite this article: Loss S.R. et al. The impact of free-ranging domestic cats on
wildlife of the United States. Nat. Commun. 4:1396 doi: 10.1038/ncomms2380 (2012).
NATURE COMMUNICATIONS | 4:1396 | DOI: 10.1038/ncomms2380 | 7
&2013 Macmillan Publishers Limited. All rights reserved.
... Estimates of bird mortality are key to providing an overview of the magnitude of impact on wildlife (Machtans and Thogmartin 2014), because they can help elicit awareness of the role of anthropogenic factors on the direct and indirect mortality of wildlife. The annual bird mortality caused by domestic cats is estimated to be between 1.3 to four billion individuals in the USA (Loss et al. 2013), and between 100 to 350 million in Canada (Blancher 2013). To give a 2003). ...
... On the basis of previous studies, bird mortality estimates are the product of the count of domestic cats and the rate of birds killed by them (Loss et al. 2013). Such parameters are often obtained from multiple methodological approaches, including surveys (Woods et al. 2003, Kays and DeWan 2004, Mori et al. 2019) and local studies on predation by domestic cats (Gillies andClout 2003, Seymour et al. 2020), advancements of geographic information systems over vast areas (Murphy et al. 2019), and the systematic review of existing literature on wildlife predation (Loss et al. 2013). ...
... On the basis of previous studies, bird mortality estimates are the product of the count of domestic cats and the rate of birds killed by them (Loss et al. 2013). Such parameters are often obtained from multiple methodological approaches, including surveys (Woods et al. 2003, Kays and DeWan 2004, Mori et al. 2019) and local studies on predation by domestic cats (Gillies andClout 2003, Seymour et al. 2020), advancements of geographic information systems over vast areas (Murphy et al. 2019), and the systematic review of existing literature on wildlife predation (Loss et al. 2013). Then, researchers impose probability distributions on the data to develop confidence intervals (Blancher 2013, Loss et al. 2013, Murphy et al. 2019. ...
... Although higher survival in populations from urban areas has been found in different bird species (e.g., Hõrak & Lebreton 1998, Anderies et al. 2007, Varner et al. 2014, some factors may negatively affect survival of birds staying in the cities. Domestic predators, such as cats Felis catus or dogs Canis lupus familiaris, are often abundant in urban environments, which can have profound effects on birds (Loss et al. 2013). Large glass surfaces and vehicle traffic can cause collision mortality (Hager et al. 2008). ...
... Many raptor species are poorly pre-adapted to survive in the urban landscape and avoid cities (Luniak 2004), but domestic cat and dog predation are important anthropogenic causes of bird mortality (Erickson et al. 2005). However, animal control law enforcement efforts tend to be more strictly enforced for dogs than for cats (Dauphine & Cooper 2009) and free-ranging dog populations are normally effectively controlled, while cats are a major threat to birds (Erickson et al. 2005, Loss et al. 2013. ...
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Survival of adults is a key demographic parameter affecting avian population dynamics. In urban areas, e.g., city parks, birds stay in winter in large numbers where they have access to a multitude of food sources due to human activities, which is one of the key factors that attract birds into the cities. Our study estimates apparent survival of mallard ducks Anas platyrhynchos between non-breeding seasons in a small town in the coldest region in northeastern Poland between 2005 and 2017. We found lower survival estimates for females (juveniles: 0.54; adults: 0.59) than males (juveniles: 0.76; adults: 0.72) and probabilities of resighting individuals in the next non-breeding season were higher if the bird was resighted in the study area during the prior breeding period. Thus, we conclude that sedentary mallards from the local urban population have relatively high survival, which may be explained by lower pressure from raptors, lack of hunting and higher winter temperatures in the urban site. Additionally, winter temperature was negatively related to resighting probability in the next non-breeding season. Resighting probability was time-dependent with a bimodal pattern with maximal estimates of 0.48 in. These results are most likely related to volunteers' activity that increased due to organized official competition with special awards during those seasons. Considering the fact that the type of ring (metal or plastic coloured) significantly influenced the probabilities of resighting of individuals, it is recommended that apparent survival studies on birds be conducted using colour rings. Moreover, we encourage to collect more capture-mark-recapture data to enable accurate estimations of duck survival, which not the least is a prerequisite for successful management and conservation efforts.
... We had to exclude the brown rat from the analysis, because there were too little field data to produce reliable species distribution maps. Also domestic cats (Felis catus), and especially free-roaming cats, can cause substantial mortality in wildlife (Loss et al., 2013). However, data on registered pet cats, to get an idea of the density, are not accessible because of the privacy law. ...
... A região do SESC Interlagos possui algumas questões antrópicas que afetam diretamente e negativamente a diversidade local: 1) presença de um grupo introduzido de saguis -sagui-de-tufo-branco [Callithrix jacchus (Lineu, 1758)], sagui-de-tufo-preto [Callithrix penicillata (É. Geoffroy, 1812)] e possíveis híbridos -, os quais são animais que predam ovos e filhotes das aves (Alexandrino et al., 2012); 2) presença constante de cachorros e gatos domésticos, que entram na unidade, atacando ninhos, filhotes e aves adultas, sendo um problema global (Loss et al., 2013) e já mencionado para a represa do Guarapiranga (Schunck et al., 2020c); 3) presença de uma quantidade grande de lixo sólido (plásticos) na margem da represa Billings, causando acidentes com as aves aquáticas (Ryan, 2018); 4) presença de vidros mal sinalizados, que possibilitam a colisão de aves, sendo este um problema amplamente conhecido (Basílio et al., 2020); 5) presença abundante da exótica palmeira-real ou seafortia [Archontophoenix cunninghamiana (H. Wendl.) ...
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O conhecimento ornitológico do município de São Paulo vem sendo produzido por naturalistas, pesquisadores e observadores de aves há 200 anos, mas parte destas informações ainda não foram organizadas, avaliadas e publicadas. Com base neste cenário, apresentamos uma compilação de dados históricos e atuais sobre a avifauna da região do Sesc Interlagos, sudeste do município. Entre 1964 e 2020, foram registradas 150 espécies, das quais, 15 são endêmicas da Mata Atlântica, 13 migratórias e uma ameaçada de extinção. Deste total, 21 foram registradas até a década de 1970 e 141 a partir de 1995, com sete táxons que podem estar extintos localmente devido ao desmatamento. Os dados organizados mostram a importância das coletas científicas, dos projetos feitos por universitários, das plataformas online de observação de aves, das ações de restauração florestal realizadas na unidade, e das atividades educativas promovidas nas últimas décadas pelo Sesc Interlagos, incluindo ações de observação de aves e sensibilização ambiental. Este esforço amostral faz desta região uma das mais conhecidas ornitologicamente do município de São Paulo, mas a presença de espécies animais e vegetais exóticas, animais domésticos ferais e grande quantidade de lixo na margem da represa Billings, são grandes ameaças que precisam ser controladas.
... Although the populations (mainly neutered individuals) and study sites (closed enclosure/rooms) prevent the generalisation of our findings to overall cat populations, this study concerns a significant part of them and provides a design better suited for scientific analyses. Nowadays, more and more pet cats are living in captivity with reduced access to the outdoors, especially in areas where their impact on surrounding wildlife is becoming problematic [45]. ...
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The plastic nature of cat behaviour allows this “friendly symbiont” of humans to adapt to various housing conditions. Beyond daylight, one could wonder if other environmental factors affect its patterns. Yet, how its activity and feeding rhythms are impacted by its environment is rarely studied in standardised conditions between populations. We compared the behaviour of cats living in a 29 m2 indoor room and cats living in a 1145 m2 outdoor enclosure, tracking them simultaneously in summer for 21 days, with advanced technologies. Both populations received daylight but weather fluctuations only occurred outdoors. Bimodality was detected in the activity and feeding rhythms of both groups, while twilight triggered crepuscular peaks. Daily, the outdoor population covered more distance (4.29 ± 0.27 km; p < 0.001) and consumed more food (67.44 ± 2.65 g; p < 0.05) than the indoor population (2.33 ± 0.17 km, 57.75 ± 2.85 g, respectively), but displayed less rhythmic behaviours, assumedly because of rhythm disruptors met only in outdoor conditions. Finally, outdoor housing seemed to promote the exploratory behaviour of the cats at night, while indoor housing increased both meal frequency (p = 0.063) and the impact of human interactions on the feeding rhythms of the cats.
... Contrary to the ample evidence of wild animals impacted by F. catus in many parts of the world, its current impact on populations remains uncertain (Trouwborst et al. 2020). Some researchers suggest that, for a more complete understanding of the situation of domestic cats impact on wildlife, it is necessary to know detailed information and aspects related to the availability of potentially affected species, the hunting habits in different occupied landscapes, the spatio-temporal hunting patterns, and the hunting taxonomic spectra from both house and feral individuals (Medina et al. 2008;Tschanz et al. 2011;Loss et al. 2013). Similarly, beyond estimating the mortality rate, it is important to identify the nature of the hunted species (e.g., native or non-native, common or rare, threatened, migratory, endemic, among others) to recognize the implications related to its conservation. ...
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El gato doméstico es una especie invasora que ocasiona problemas para la vida silvestre en todo el mundo, pero el conocimiento de sus efectos en la región neotropical es escaso. En este estudio realizamos una aproximación sobre la mortalidad de fauna silvestre ocasionada por este felino en áreas urbanas y rurales de la región Caribe de Colombia. Encontramos 107 registros de cacería de 31 especies entre anfibios, reptiles, aves y mamíferos, de las cuales se destaca a Cnemidophorus sp. por tener el mayor número de casos (31). Adicionalmente, encontramos un registro de caza de una especie migratoria, Porzana carolina, y dos subespecies endémicas del Caribe colombiano (Erythrolamprus melanotus lamari y Ameiva bifrontata divisa). Los resultados de este trabajo son los primeros documentados para el país, advirtiendo del impacto potencial que puede estar generando el gato doméstico sobre la biodiversidad colombiana. The Domestic cat is an invasive species causing problems for wildlife throughout the world, but knowledge of its effects in the Neotropical region is scarce. In this study, we made an approximation of cases of mortality of wildlife caused by this feline in urban and rural areas of the Caribbean region of Colombia. We found 107 hunting records of 31 species among amphibians, reptiles, birds and mammals, of which highlights Cnemidophorus sp. for having the highest number of cases (31). Additionally, we found a hunting record of a migratory species, Porzana carolina, and two
... Previous studies corroborate this expectation as dogs enforce interference competition to alter space use and have been observed harassing and killing chilla(Silva- Rodríguez et al. 2010b). A lack of a negative response from chillas to dogs using our occupancy framework could indicate that foxes were avoiding dogs at finer spatial or temporal scales, or that dog density was not sufficiently high to elicit a spatial avoidance (Zapata-Ríos and Branch Fragmentation can facilitate the spread of invasive species through numerous pathways, such as roads increasing the occurrence of dogs(Loss et al. 2013;Moreira-Arce et al. 2015). Yet, few occupancy studies have looked at the impacts of both dogs and habitat loss and fragmentation on native carnivores. ...
Anthropogenic habitat destruction is one of the major causes of biodiversity loss, driving species declines across the planet. The resultant human-modified landscapes are not detrimental for all species. Some species such as small to medium-sized habitat generalist carnivores (hereafter referred to as ‘mesocarnivores’) are able to thrive because of the exclusion of natural enemies and anthropogenic sources of food. With the benefits of human-modified landscapes come novel threats, such as increased exposure to hunting and introduced antagonists. Mesocarnivores may respond to these threats with changes in space and time use, with potential consequences for species interactions. In this dissertation, I examine how drivers of mesocarnivore space and time use align with physical characteristics of the human-modified landscape and associated factors, and what implications these results have for interactions between native species. I do this using empirical work across two temperate systems (Chapters II, III, and IV), and a simulation model (Chapter V).
... Furthermore, cats can eat more than one mouse. Cats not fed by humans kill, and probably consume, in average about one mammal per day, consisting of mice, voles and others [33,34]. In addition, owners of cats included in the present study described somnolent and dead mice being detected outside of traps i.e., mice more easily caught and consumed by cats and other carnivores. ...
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Background Alpha-chloralose (AC) is a compound known to be toxic to various animal species and humans. In 2018 and 2019 an increase in suspected cases of AC poisoning in cats related to the use of AC as a rodenticide was reported to national veterinary and chemical authorities in Finland, Norway and Sweden by veterinarians working in clinical practices in respective country. The aims of this study were to prospectively investigate AC poisoning in cats, including possible secondary poisoning by consuming poisoned mice, and to study metabolism and excretion of AC in cats through analysis of feline urine. Methods Data on signalment, history and clinical findings were prospectively collected in Finland, Norway and Sweden from July 2020 until March of 2021 using a questionnaire which the attending veterinarian completed and submitted together with a serum sample collected from suspected feline cases of AC-poisoning. The diagnosis was confirmed by quantification of AC in serum samples. Content of AC was studied in four feline urine samples, including screening for AC metabolites by UHPLC-HRMS/MS. Bait intake and amount of AC consumed by mice was observed in wild mice during an extermination of a rodent infestation. Results In total, 59 of 70 collected questionnaires and accompanying serum samples were included, with 127 to 70 100 ng/mL AC detected in the serum. Several tentative AC-metabolites were detected in the analysed feline urine samples, including dechlorinated and oxidated AC, several sulfate conjugates, and one glucuronic acid conjugate of AC. The calculated amount of AC ingested by each mouse was 33 to 106 mg with a mean of 61 mg. Conclusions Clinical recognition of symptoms of AC poisoning in otherwise healthy cats roaming free outdoors and known to be rodent hunters strongly correlated with confirmation of the diagnosis through toxicological analyses of serum samples. The collected feline exposure data regarding AC show together with the calculation of the intake of bait and subsequent AC concentrations in mice that secondary poisoning from ingestion of mice is possible. The results of the screening for AC metabolites in feline urine confirm that cats excrete AC both unchanged and metabolized through dechlorination, oxidation, glucuronidation and sulfatation pathways.
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Island ecosystems are, in general, more vulnerable to change than are those on continents, and the West Indies are no exception. In the past 155 years a minimum of 7-12 extinctions and 12-13 extirpations of amphibians and reptiles have occurred in the West Indies. In the Lesser Antilles (and other small islands), most extirpations can be attributed to the introduction of alien predators (primarily the mongoose, but also cats and dogs). Certain species appear more sensitive to predator introductions than others (e.g., teiid lizards of the genus Ameiva and colubrid snakes of the genera Alsophis and Liophis). On mongoose-infested islands, other factors were investigated (human population density, island area, physiographic complexity), but none absolved the mongoose as the primary agent of extirpation. In the Greater Antilles, although introduced predators have had a negative impact, extinctions due to habitat destruction appear more likely due to the potentially stenoecious adaptation of many taxa (e.g., tree crown-, buttress-, and bromeliad-dwelling species).
The hypothesis that predation on eggs and chicks by ferrets (Mustela furo) and cats (Felis catus) was limiting the productivity of North Island weka (Gallirallus australis greyi), was tested by removing predators from the home ranges of four breeding pairs of weka. Reproduction by four other breeding pairs was monitored to provide a control. I was not able to follow the breeding success of some weka because they died or removed their radio transmitters. Two of the pairs breeding in predator-removal areas reared five chicks to independence, while two control pairs reared no chicks to independence after three breeding attempts. It was not possible to draw solid conclusions from group comparison data gained from so few individuals. Because it is necessary to identify the factors preventing weka recovery now, I suggest an alternative way to gather reliable data about rare species like weka. Single subject experimental designs like those developed in the social sciences offer an alternative route for investigating agents of decline in rare species; such a design would have been preferable to the one used in the present study. A common experimental procedure in single subject studies is the A-B-A series or some variant of it where A and B refer to experimental conditions with A being the control and B the treatment. Treatments are switched on and off for individuals (e.g., animals, or areas) which are considered representative of the study population. Well designed, replicated single subject studies might allow data to be used even after unplanned alterations to experimental conditions. The results of such studies would be cumulative, interpretable and more readily publishable. For some species all that may be required is a reanalysis of existing data.
Predation by house cats (Felis catus) is one of the largest human-related sources of mortality for wild birds in the United States and elsewhere, and has been implicated in extinctions and population declines of several species. However, relatively little is known about this topic in Canada. The objectives of this study were to provide plausible estimates for the number of birds killed by house cats in Canada, identify information that would help improve those estimates, and identify species potentially vulnerable to population impacts. In total, cats are estimated to kill between 100 and 350 million birds per year in Canada (> 95% of estimates were in this range), with the majority likely to be killed by feral cats. This range of estimates is based on surveys indicating that Canadians own about 8.5 million pet cats, a rough approximation of 1.4 to 4.2 million feral cats, and literature values of predation rates from studies conducted elsewhere. Reliability of the total kill estimate would be improved most by better knowledge of feral cat numbers and diet in Canada, though any data on birds killed by cats in Canada would be helpful. These estimates suggest that 2-7% of birds in southern Canada are killed by cats per year. Even at the low end, predation by house cats is probably the largest human-related source of bird mortality in Canada. Many species of birds are potentially vulnerable to at least local population impacts in southern Canada, by virtue of nesting or feeding on or near ground level, and habitat choices that bring them into contact with human-dominated landscapes where cats are abundant. Because cat predation is likely to remain a primary source of bird mortality in Canada for some time, this issue needs more scientific attention in Canada.
Approximately 300 digestive tracts of fur animals obtained mostly during the winter trapping season and 560 scats from animals live-trapped on the Patuxent Research Refuge near Laurel, Maryland, were analyzed. The resulting data are summarized and a brief description of the area and important habitat types is given. The animals studied include the raccoon, red fox, gray fox, mink, New York weasel, skunk, opossum, and house cat.