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110 PRHSJ Vol. 37 No. 2 • June, 2018
Health and Ecological Aspects of Stray Cats in
Old San Juan, Puerto Rico: Baseline Information
to Develop an Effective Control Program
Jessica Castro-Prieto; María José Andrade-Núñez
Department of Environmental Science, University of Puerto Rico, Rio Piedras
Campus, San Juan, PR
The author/s has/have no conflict/s of interest to disclose.
Address correspondence to: Jessica Castro-Prieto, Department of Environmental
Science, University of Puerto Rico, Rio Piedras Campus, PO Box 70377, San Juan,
PR 00936-8377. Email: jessica.castroprieto@upr.edu
The overpopulation of stray cats in urban areas represents a potential risk for
humans, as stray cats may carry diseases, such as toxoplasmosis, and virus such
as rabies, the feline immunodeficiency, and the feline leukemia. In Old San Juan, a
historic neighborhood and one of the most touristic places in Puerto Rico, there is
an overpopulation of stray cats. In this study, we generated baseline information
fundamental to developing a successful control program by estimating the stray cat
population size, density, and spatial distribution. Furthermore, we quantified the
number of neutered cats and developed a spatial database to include information
about the external physical condition of each individual. We estimated a population
of 178 (±21) cats, with a density of 3.6 cats/ha. Overall, we observed 209 cats, from
which 149 (71%) were identified as new and 60 (29%) were recaptured. We found
stray cats had a significant non-random and clustered spatial distribution (z-score =
-19.39 SD; ratio = 0.29; p<0.0001), with an observable larger abundance in residential
zones where food was provided. A total of 105 (70%) cats were neutered, and 32
(21%) individuals exhibited very poor physical conditions, including skin problems,
scars, underweight, and blindness. We concluded that the ecological and descriptive
data generated in this study are essential for an effective control of stray cats and
their potential impacts on humans living in this neighborhood. [P R Health Sci J
2018;37:110-114]
Key words: Felis catus, Feral cats, TNR program, Population control, Urban cats
The domestic cat (Felis catus) is one of the first domesticated
species and most popular pet in the world (1), with a total
population estimated to be approximately 400 million
(2, 3). A global problem of free-ranging cats in urban areas
has required controlling their populations, as stray cats pose a
potential risk for human health and safety. Stray cats may carry
diseases, such as rabies and toxoplasmosis, and such viruses as
the feline immunodeficiency vir us and the feline leukemia virus
(4, 5). These infectious diseases can be transmitted to humans,
indoor pets, and wildlife, causing serious medical conditions,
including miscarriage, blindness, and even death (6, 7, 8, 9). In
addition to this, stray cats are carnivores and skilled predators,
representing one of the most important causes of mortality for
birds and mammals in many countries (10, 11, 12, 13, 14) and
being a major contributor of species extinction on many islands
where they have been introduced (15, 16).
Traditional management programs to control, reduce, and
eventually remove colonies of stray cats from urban areas
include trap and relocation to shelters for later adoption and
euthanasia (17). Another widely implemented program is trap,
neuter, and return (TNR), which consists of trapping cats,
surgically sterilizing (or neutering) them, and returning them to
the streets (17, 18). Despite the fact that TNR in combination
with a successful adoption program reduced some colonies of
stray cats in various urban areas of United States (19, 20), this
method was ineffective in many other circumstances (21).
First, TNR was ineffective when populations were open (where
migration and emigration occur) or contained more than 50
individuals (21). Second, positive effects on reducing the size
of a given population were observed after several generations,
post-implementation, but when TNR was discontinued, the
population in question rapidly increased (15, 22). Third, TNR
was ineffective in addressing other impacts associated with large
populations of stray cats, including predation, diseases, and
odors from the cats’ urine and feces in public areas (23, 24, 25,
26, 27). In this regard, TNR is not supported by the scientific
community, as it is not a tangible solution for the different issues
related to colonies of stray cats in urban areas (28, 15, 17).
In Old San Juan, an urban neighborhood that is one of the
most popular touristic destination in Puerto Rico, there is a
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Castro-Prieto & Andrade-Núñez
problem of stray-cat overpopulation. Stray cats have been an
issue of public debate in this neighborhood for a while. By the
year 2000, the United States National Park Services and other
federal agencies proposed a plan to control stray cats that was
rejected by the local community, as it included euthanasia
(29). Since then, both a local non-governmental organization
called Save a Gato (SaG) and a cat shelter were established
to advocate for the welfare of the cats under discussion; and
started implementing TNR as a strategy to reduce and control
the population of stray cats in Old San Juan. As a means of
controlling the stray-cat population in this neighborhood, a
program that combined TNR and adoption was implemented
10 years ago, but it remains unknown how effective that program
has been. Furthermore, it is unclear if stray cats represent an
important health issue for residents and visitors that would
require action from governmental agencies.
In this study, we estimated the size and spatial distribution
of the population of stray cats inhabiting Old San Juan,
fundamental baseline information needed to assess population
trends, TNR effectiveness, and the potential health impacts on
humans. Furthermore, we quantified the number of neutered
cats, and developed a spatial database that includes information
about the external physical condition of each animal to facilitate
later identification, tracking, and monitoring.
Materials and Methods
Study area
Old San Juan is a historic Spanish colonial urban area in San
Juan, Puerto Rico’s capital city; it is located on the northeast
coast of the island (Fig. 1). This area has a year-round human
population of approximately 100,000, but receives more than 1
million tourists each year. Our study was
conducted in an area of approximately
49 hectares, limited by Norzagaray
Street to the north and east, Paseo de
la Princesa and the docks to the south,
and Paseo del Morro to the west. The
area comprises 868 parcels that are used
as commercial centers (62%), high-
population residential zones (31%),
and public areas (7%). Due to access
limitation and time constraints, we
excluded important sites that we knew
had large colonies of stray cats, which
sites included La Perla, La Puntilla,
and most of the rocky shore of Paseo
del Morro.
Population size, density, and spatial
distribution
We conducted a single 2-day
visual
encounter survey (VES), which
consisted
of counting the number of
individuals present in each survey area over a specific time
period (30). This technique is widely used in ecological research
to estimate the diversity and abundance in a specific location
or for a given species (31). In this study, 2 observers covered
the north/south streets and 2 others covered the east/west
streets; both pairs of observers were in action from 8:00 AM
to 1:00 PM on the pertinent 2 days (both in May of 2013). To
estimate the population size (N), we used the Petersen method
(32), which uses a single episode of marking (or documenting)
animals, followed by a second-day survey for recapturing or
“re-sighting” individuals.
The population size (N) was estimated as follows:
N = – 1
(M + 1)(C + 1)
(R + 1)
where N = Estimate of total population size
M = Total number of animals “captured and marked” on the
first day of the survey
C = Total number of animals “captured and marked” on the
second day of the survey
R = Number of animals “recaptured” on the second day of
the survey
We calculated normal approximation confidence intervals for
the Petersen method results as follows:
R
__
C
1
__
2C
R
__
C
R
__
C
α
++
(1 – f ) 1 –
(C – 1)
where:
ƒ = fraction of total population sampled in the second
sample = R
__
M
Figure 1. Map of Old San Juan depicting our study site (thick, black line) and the city zoning districts.
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112 PRHSJ Vol. 37 No. 2 • June, 2018
Castro-Prieto & Andrade-Núñez
1/2C = correction for continuity
zα = standard normal deviate for (1-α) level of confidence,
1.96 (for 95% confidence limits)
Once a cat was encountered, we collected the following
information about that individual: fur color and pattern, eye
color, probable gender, life stage (i.e., kitten, young, mature),
scars, physical condition, presence (or not) of a collar, behavior
(e.g., sleeping, walking), alone or in a group, and whether the
cat was neutered or not (indicated by a cut in the tip of 1 ear).
In addition, we photographed the individual, registered the
geographic coordinates of the site of encounter using a GPS, and
provided a brief description of the site, including the presence
(or lack) of feeding stations (food dishes). The information
for each individual was entered using a unique identification
code. Since in this study the cats were not manipulated, we did
not need permission from the Institutional Animal Care and
Use Committee (IACUC) to conduct the surveys. Finally, we
calculated the Euclidean distance between cats location points
and the feeding stations using the average nearest neighbor tool
in ArcGIS 9.3.
Results
We estimated a population of 178 (±21) cats, with a density
of 3.6 cats/ha. Overall, we observed 209 cats, from which 149
(71%) were identified as “new” individuals, and 60 (29%)
were “recaptured,” as they were identified on the first day and
re-sighted on the second day of the survey. We found that 105
(70%) of the individuals were neutered, and 32 (21%) presented
visible health issues, including scabies, scars, hairless areas,
black spots in the mouth and/or around the eyes and ears, and
blindness, while some cats were extremely underweight, despite
the fact that large amounts of food were provided (Fig. 2).
We found that stray cats had a significant non-random and
clustered spatial distribution (z-score = -19.39 SD; ratio = 0.29;
0.01 significance level; p<0.0001), with an observable greater
abundance in residential and public-zoned parcels where feeding
stations were available (Fig. 3).
Discussion
Our study provides the first assessment of the population size
and spatial distribution of stray cats in an urban neighborhood
in Puerto Rico. Furthermore, we provide a description of 149
cats and their spatial locations, which data might facilitate the
management and monitoring of the cats.
Although cat numbers in Old San Juan were lower than those
of other urban areas where similar studies have been conducted
(20, 33, 3), the density of cats in this neighborhood was higher
than the densities observed in these other places. Furthermore,
we found that stray cats exhibited high site fidelity to places were
their caretakers lived or provided food, which at the same time
facilitated the identification of individuals and the estimation
of population size. VES, then, is a simple methodology for
the identification of stray cats and can be used to estimate the
population and assess the effectiveness of TNR programs in a
given urban area.
Though our was the first study to systematically quantify the
actual size of the population of stray cats in Old San Juan, we
faced several limitations that should be overcome if researchers
are to generate a more accurate estimation. For example, we
underestimated the actual population size, as we were unable
to conduct cat surveys in 2 areas within Old San Juan where we
knew stray cats were abundant (i.e., Paseo del Morro and the
neighborhood of La Perla) or during the time of the day when
cats are most active (e.g., when they are fed, at sunset).
Our results suggest that the TNR program developed
to control the population of stray cats in Old San Juan has
been satisfactory, as 70% of the cats we found were neutered.
However, there is a lack of past references to assess the
effectiveness of the program in reducing the net
population size and in reducing, as well, the nuisances
associated with the presence of a large population of
stray cats. The presence of pregnant females, kittens,
and more than 40 unneutered adults observed during
our surveys suggest that the population of stray cats
will continue growing.
Though providing disease diagnostics was
beyond the scope of our study, we documented the
existence of several cats with poor external physical
conditions and of large amounts of feces in public
areas, including in a children’s playground that had a
sandbox and which was located next to the cat shelter.
Unhealthy living conditions as a consequence of
an overpopulation of stray animals could represent
a neglected source of parasites and diseases for
humans and indoor pets in this neighborhood.
Thus, diagnostics to identify contagious diseases and
parasites (such as Toxoplasma gondii) that could be
Figure 2. Examples of stray cats in Old San Juan with poor physical conditions.
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Castro-Prieto & Andrade-Núñez
transmitted from stray cats to humans are needed to better
understand the implications in terms of public health (34).
The management of stray cats in a highly human-populated
area such as Old San Juan should involve cat caretakers and
advocates, veterinarians, and governmental agencies.
Resumen
La sobrepoblación de gatos callejeros en áreas urbanas
representa un riesgo potencial para los seres humanos, ya que
los primeros pueden portar enfermedades como toxoplasmosis
y virus como la rabia, la inmunodeficiencia felina y la leucemia
felina. En el Viejo San Juan, un barrio histórico y uno de los
lugares más turístico de Puerto Rico, hay una sobrepoblación de
gatos callejeros. En este estudio, hemos generado información
de base fundamental para desarrollar un programa de control
exitoso mediante la estimación del tamaño poblacional,
densidad y distribución espacial de gatos callejeros. Además,
cuantificamos el número de gatos castrados, y desarrollamos
una base de datos espacial con información sobre la condición
física externa de cada individuo. Se estimó una población
de 178 ± 21 gatos, con una densidad de 3.6 gatos / ha. En
general, observamos 209 gatos de los cuales 149 (71%)
fueron identificados como nuevos, y 60 (29%) fueron
recapturados. Encontramos que los gatos callejeros tenían
una distribución espacial significativa no aleatoria y agrupada
(puntuación Z = -19.39 SD, Ratio = 0.29, p <0.0001), con
una mayor abundancia en las zonas residenciales donde se les
proporcionaba alimento. Un total de 105 gatos (70%) estaban
castrados, y 32 (21%) individuos mostraron condiciones
físicas muy pobres, incluyendo: problemas
de piel, cicatrices, bajo peso y ceguera.
Concluimos que los datos ecológicos y
descriptivos generados en este estudio son
esenciales para el control efectivo de los
gatos callejeros y los impactos potenciales
en los seres humanos que habitan en este
vecindario.
Acknowledgments
We would like to thank Michelle Scharer
for her editing and major comments, all
of which helped improve the content
of this manuscript. Thanks to Colibri
Sanfiorenzo-Barnhard and Johnny Lugo-
Vega for their help during field work. We
also thank IGERT fellows and professors,
as well as the persons that agreed to
participate in the interviews. This study
was supported by NSF IGERT under grant
#0801577.
References
1. Driscoll CA, Macdonald DW, O’Brien SJ. From wild animals to domestic
pets, an evolutionary view of domestication. Proc Natl Acad Sci U S A
2009;16:9971–9978.
2. Lowe S, Browne M, Boudjelas S, De Poorter M. 100 of the world’s worst
invasive alien species: A selection from the Global Invasive Species Data-
base. The Invasive Species Specialist Group. Species Survival Commis-
sion. World Conservation Union. 2000. Available at: Url: http://www.
issg.org/pdf/publications/worst_100/english_100_worst.pdf. Accessed
July 21, 2015.
3. Schmidt PM, Lopez RR, Pierce BL. Estimating free-roaming cat densities
in urban areas: comparison of mark-resight and distance sampling. Wildl
Biol Pract 2007;3:18–27.
4. Duarte A, Castro I, Pereira da Fonseca IM, Almeida V, Madeira de Car-
valho LM, Meireles J, et al. Survey of infectious and parasitic diseases in
stray cats at the Lisbon Metropolitan Area, Portugal. J Feline Med Surg
2010;12:441–446.
5. Spada E, Proverbio D, della Pepa A, Perego R, Baggiani L, DeGiorgi
GB, et al. Seroprevalence of feline immunodeficiency virus, feline leu-
kaemia virus and Toxoplasma gondii in stray cat colonies in northern
Italy and correlation with clinical and laboratory data. J Feline Med Surg
2012;14:369–377.
6. Conrad PA, Miller MA, Kreuder C, James ER, Mazet J, Dabritz H, et al.
Transmission of Toxoplasma: Clues from the study of sea otters as senti-
nels of Toxoplasma gondii flow into the marine environment. Int J Parasi-
tol 2005;35:1155–1168.
7. Danner RM, Goltz DM, Hess SC, Banko PC. Evidence of Feline Immuno-
deficiency Virus, Feline Leukemia Virus, and Toxoplasma gondii in Feral
cats on Mauna Kea, Hawaii. J Wildl Dis 2007;43:315–318.
8. Gerhold RW, Jessup DA. Zoonotic diseases associated with free-roaming
cats. Zoonoses Public Health. 2013;60:189–195.
9. VanWormer E, Conrad PA , Miller MA, Melli AC, Carpenter TE, Mazet
JA. Toxoplasma gondii, source to sea: higher contribution of domestic
felids to terrestrial parasite loading despite lower infection prevalence.
Ecohealth 2013;10:277–289.
10. Mitchell JC, Beck RA. Free-ranging domestic cat predation on native ver-
tebrates in rural and urban Virginia. Va J Sci 1992;43:197–208.
Figure 3. Number of cats (circles) and their distribution in Old San Juan overlapped to parcel
zoning and feeding stations (triangles). Examples of the living conditions of the stray cats
and feeding stations are shown.
07 - 16-16 (1532) FL - Castro & Andrade.indd 113 6/6/2018 9:08:32 AM
Stray Cats in Urban Areas
114 PRHSJ Vol. 37 No. 2 • June, 2018
Castro-Prieto & Andrade-Núñez
11. Dickman CR. Overview of the impacts of feral cats on Australian native
fauna. Australian Nature Conservation Agency. Australian Government,
Department of the Environment. 1996. Available at: Url: https://www.
pestsmart.org.au/wp-content/uploads/2010/03/impacts-feral-cats.pdf.
Accessed June 21, 2014.
12. Woods M, McDonald RA, Harris S. Predation of wildlife by domestic cats
Felis catus in Great Britain. Mammal Rev 2003;33:174–188.
13. Winter L, Wallace GE. Impacts of feral and free-ranging cats on bird spe-
cies of conservation concern: A five-state review of New York, New Jersey,
Florida, California, and Hawaii. American Bird Conservancy. UNL Digi-
tal Commons. 2006. Available at: Url: http://digitalcommons.unl.edu/
icwdmother/28. 2006. Accessed May 7, 2014.
14. Loss SR, Will T, Marra PP. The impact of free-ranging domestic cats on
wildlife of the United States. Nat Commun 2013;4:1396.
15. Dauphiné N, Cooper RJ. Impacts of free-ranging domestic cats (Felis ca-
tus) on birds in the United States: a review of recent research with conser-
vation and management recommendations. In Fourth International Part-
ners in Flight Conference: Tundra to Tropics. McAllen. 2009;205–219.
Available at: Url: http://www.partnersinflight.org/pubs/McAllenProc/
articles/PIF09_Anthropogenic%20Impacts/Dauphine_1_PIF09.pdf.
Accessed November 30, 2013.
16. Rodríguez-Durán A, Pérez J, Montalbán MA, Sandoval JM. Predation
by Free-Roaming Cats on an Insular Population of Bats. Acta Chiropt
2010;12:359–362.
17. Peterson MN, Hartis B, Rodriguez S, Green M, Lepczyk C A. Opinions
from the Front Lines of Cat Colony Management Conflict. PLoS One.
2012;7:e44616. doi:10.1371/journal.pone.0044616.
18.
Kortis B. Neighborhood Cats TNR Handbook: The guide to Trap-
Neuter-Return for the Feral Cat Caretaker. 2nd ed. New York, NY:
Neighborhood Cats, Inc. 2013. Available at: Url: s3.amazonaws.com/
jo.beta.bucket/neighborhoodcats/ckeditor_assets/data/100/nc_tnr_
handbook_2d_ed_2_7mb.pdf. Accessed: April 30, 2013.
19. Centonze LA, Levy JK. Characteristics of free-roaming cats and their
caretakers. J Am Vet Med Assoc 2002;220:1627–1633.
20. Levy JK, Gale DW, Gale LA. Evaluation of the effect of a long-term trap-
neuter-return and adoption program on a free-roaming cat population. J
Am Vet Med Assoc 2003;222:42–46.
21.
Castillo D, Clarke AL. Trap/neuter/release methods ineffective in control-
ling domestic cat “colonies” on public lands. Nat Area J 2003;23:247–253.
22. Wald DM, Jacobson SK, Levy JK. Outdoor cats: Identifying differences
between stakeholder beliefs, perceived impacts, risk and management.
Biol Conserv 2013;167:414–424.
23. Scott KC, Levy JK, Crawford PC. Characteristics of free roaming
cats evaluated in a trap-neuter-return program. J Am Vet Med Assoc
2002;221:1136–1138.
24.
Andersen MC, Martin BJ, Roemer GW. Use of matrix population mod-
els to estimate the efficacy of euthanasia versus trap-neuter- return
for management of free-roaming cats. J Am Vet Med Assoc 2004;225:
1871–1876.
25. Barrows PL. Professional, ethical, and legal dilemmas of trap-neuter-re-
lease. J Am Vet Med Assoc 2004;225:1365–1369.
26. Longcore T, Rich C, Sullivan LM. Critical assessment of claims re-
garding management of feral cats by trap-neuter-return. Conserv Biol
2009;23:887–894.
27. Lepczyk CA, Dauphiné N, Bird DM, Conant S, Cooper RJ, Duffy DC,
et al. What conservation biologists can do to counter trap-neuter-return:
response to Longcore et al. Conserv Biol 2010;24:627–629.
28. Berkeley EP. TNR: Past, Present and Future: A History of the Trap-Neu-
ter-Return Movement. Washington, DC: Alley Cat Allies; 2004.
29.
United States Department of Agriculture. Management of feral and
free-ranging cat populations to reduce threats to human health and
safety and impacts to native wildlife species in the Commonwealth of
Puerto Rico. Washington, DC: Animal and Plant Health Inspection
Service and Wildlife Services, United States Department of Agricul-
ture; 2003
30. Flint WD, Harris RN. The efficacy of visual encounter surveys for popu-
lation monitoring of Plethodon punctatus (Caudata: Plethodontidae). J
Herpetol 2005;39:578–584.
31. Dodd CK, ed. Amphibian Ecology and Conservation: A Handbook of
Techniques. New York, NY: Oxford University Press Inc.; 2009.
32.
Petersen, CGJ. The yearly immigration of young plaice into the Lim-
fjord from the German Sea. Report of the Danish Biological Sta-
tion, 1895.6. 1896. Available at: Url: https://archive.org/stream/
reportofdanishbi06dans#page/n7/mode/2up. Accessed July 15,
2013.
33. Levy J, Woods J, Turick S, Etheridge DL. Number of unowned free-roam-
ing cats in a college community in the southern United States and char-
acteristics of community residents who feed them. J Am Vet Med Assoc
2003;223:202–205.
34. Diakou A, Di Cesare A, Accettura PM, Barros L, Iorio R, Paoletti B, et
al. Intestinal parasites and vector-borne pathogens in stray and f ree-roam-
ing cats living in continental and insular Greece. PLoS Negl Trop Dis
2017;11:e0005335.
07 - 16-16 (1532) FL - Castro & Andrade.indd 114 6/6/2018 9:08:32 AM
