Other environmental factors affects more Island foxes diet than competition with feral cats

Cypher, B.L. , Kelly E.C., Ferrara, F.J., Drost C.A., Westall, T.L. & Hudgens, B.R. 2017. Diet patterns of island foxes on San Nicolas Island relative to feral cat removal. Pacific Conservation Biology 23(2) 180-188

Island foxes (Urocyon littoralis) are a species of conservation concern that occur on six of the Channel Islands off the coast of southern California. We analysed island fox diet on San Nicolas Island during 2006–12 to assess the influence of the removal of feral cats (Felis catus) on the food use by foxes. Our objective was to determine whether fox diet patterns shifted in response to the cat removal conducted during 2009–10, thus indicating that cats were competing with foxes for food items. We also examined the influence of annual precipitation patterns and fox abundance on fox diet. On the basis of an analysis of 1975 fox scats, use of vertebrate prey – deer mice (Peromyscus maniculatus), birds, and lizards – increased significantly during and after the complete removal of cats (n = 66) from the island. Deer mouse abundance increased markedly during and after cat removal and use of mice by foxes was significantly related to mouse abundance. The increase in mice and shift in item use by the foxes was consistent with a reduction in exploitative competition associated with the cat removal. However, fox abundance declined markedly coincident with the removal of cats and deer mouse abundance was negatively related to fox numbers. Also, annual precipitation increased markedly during and after cat removal and deer mouse abundance closely tracked precipitation. Thus, our results indicate that other confounding factors, particularly precipitation, may have had a greater influence on fox diet patterns.

No evidence of dietary shift by native predators in sympatry with feral cats

Phillips, R. B., Winchell, C. S., & Schmidt, R. H. (2007). Dietary overlap of an alien and native carnivore on San Clemente Island, California. Journal of Mammalogy, 88(1), 173-180.


Predation by feral cats (Felis catus) is recognized as a major threat to native fauna worldwide, but the competitive effects of cats on native species have not been extensively studied. Cats occur on San Clemente Island, California, in sympatry with endemic island foxes (Urocyon littoralis clementae). We examined diets of cats and island foxes between years, seasons, and habitats to assess the potential for resource competition between the 2 species. Analysis of 602 cat and 958 fox feces revealed a high level of dietary overlap (O = 0.93) and relatively narrow niche breadths for both species (Bstandard Fox = 0.37; Bstandard Cat = 0.49). Despite the overlap in diet, cats and foxes appear to partition prey resources. Cats consume approximately equal proportions of arthropod (47.9%) and vertebrate (44.2%) prey, the latter primarily rodents (29.2%) and lizards (12.9%). In contrast, foxes appear to rely more on arthropods (57.7%), with plants (20.5%) and vertebrates (21.6%) occurring in lower, but roughly equal frequencies. Season appeared to have little effect on diet; however, diet did vary between habitats and years for both species. Diets of cats on San Clemente Island are consistent with those from other studies. We found no evidence of a dietary shift by foxes that were in sympatry with cats.

Involvement in a Northern California community on the feral cat problem

Lando, C. A. (2016). Building involvement in a Northern California community on a targeted public health issue: a service announcement on the feral cat problem in Chico.  Faculty of California State University, Chico

The primary purpose of this study is to examine the health and environmental issues caused by feral cats and to offer solutions to control the growth of feral cat colonies in a Northern California community. Research supports the claim that feral cats, or community cats are a community problem and a community’s responsibility. Therefore, the local government, local animal welfare groups, and concerned citizens need to work together to find viable solutions.
Furthermore, the City of Chico’s Animal Control Officer estimates there are approximately 14,000 feral cats living on the streets and in the parks of the city of Chico. Several animal welfare organizations have worked to reduce this number through adoption, offering permanent housing, or trapping, vaccinating, neutering and returning cats to their colonies. The city’s euthanasia policy is only in effect for sick animals brought into the shelter by citizens. Due to budget cuts and lack of space, the city cannot house abandoned or surrendered animals. Therefore, the city refers calls about feral cats to one of the other animal welfare agencies.
The results of this project have shown that a collaborative organization consisting of members of concerned citizens and animal welfare groups can offer the best solutions to the feral cat dilemma. Accessing information about the ways other communities have addressed the feral cat problem is helpful. Working together individual organizations can share strategies for implementing fundraising activities, publicity, grant writing, and other issues such as purchasing pet supplies and food.
In addition, California State University, Chico, needs to take a more active role in disseminating information to its students about not releasing cats at the end of the school year. This information should be provided during orientation and through the university’s newspaper. Research has shown that an ongoing public service announcement through television and radio is one of the best ways to reach the most people. Public service announcements offer information and resources available to
citizens for assistance with a feral cat problem. 

Leptospira in free-living sea lions in California and Baja California

Rosalía Avalos-Téllez, Erika M. Carrillo-Casas, Daniel Atilano-López, Carlos R. Godínez-Reyes, Efrén Díaz-Aparicio, David Ramírez-Delgado, María F. Ramírez-Echenique, Margarita Leyva-Leyva, Gerardo Suzán, and Francisco Suárez-Güemes (2016) Pathogenic Leptospira serovars in free-living sea lions in the gulf of California and along the Baja California coast of Mexico. Journal of Wildlife Diseases In-Press.


The California sea lion (Zalophus californianus), a permanent inhabitant of the Gulf of California in Mexico, is susceptible to pathogenic Leptospira spp. infection, which can result in hepatic and renal damage and may lead to renal failure and death. During summer 2013, we used the microscopic agglutination test (MAT) to investigate the prevalence of anti-Leptospira antibodies in blood of clinically healthy sea lion pups from seven rookery islands on the Pacific Coast of Baja California (Pacific Ocean) and in the Gulf of California. We also used PCR to examine blood for Leptospira DNA. Isolation of Leptospira in liquid media was unsuccessful. We found higher antibody prevalence in sea lions from the rookery islands in the gulf than in those from the Pacific Coast. Antibodies against 11 serovars were identified in the Gulf of California population; the most frequent reactions were against serovars Bataviae (90%), Pyrogenes (86%), Wolffi (86%), Celledoni (71%), and Pomona (65%). In the Pacific Ocean population, MAT was positive against eight serovars, where Wolffi (88%), Pomona (75%), and Bataviae (70%) were the most frequent. Serum samples agglutinated with more than one Leptospira serovar. The maximum titer was 3,200. Each island had a different serology profile, and islands combined showed a distinct profile for each region. We detected pathogenic Leptospira DNA in 63% of blood samples, but we found no saprophytic Leptospira. Positive PCR results were obtained in blood samples with high and low MAT titers. Together, these two methods enhance the diagnosis and interpretation of sea lion leptospirosis. Our results may be related to human activities or the presence of other reservoirs with which sea lions interact, and they may also be related to sea lion stranding.

Distribution and correlates of feral cat trapping permits in Los Angeles

Kingsley, G. (2015). Distribution and correlates of feral cat trapping permits in Los Angeles, California (doctoral dissertation, University of Southern California)

Uncontrolled populations of feral cats in urban settings have become of concern to public officials, wildlife scientists, animal rights advocates and the public in general due to the risks they pose to public health, urban wildlife, and esthetics. Solutions to the problem of unmanaged cat populations in cities have been limited in scope by the lack of actual data on feral cats and the urban geographic ranges they occupy. Full extent censuses and environmental analyses have not been collected or performed due to the resources allocations and costs involved. A method for collecting this data without the use of field crews and research summaries exists in the form of unused paper records. Past studies on the problem have used data mining of available records to model cat territories and densities (Aguilar and Farnworth 2012). This approach mitigates the cost while providing information regarding the distributions of these animals. This thesis investigates the spatial properties of feral cat populations in a large metropolitan area (Los Angeles, California) using a previously non-spatialized dataset as a proxy for concentrations of feral cats. The following case study explores two matters: 1) development of a workflow to create a spatial model of feral cat extents from geographic data brought into an analyzable format and 2) analysis of the model data to determine what, if any, variables are correlated with these distributions. The data used for the model were obtained from the City in the form of paper records and successfully imported into a Geographic Information System. Densities of applications were determined from the cleaned and geocoded records and concentrations of both raw density and patterns of clustering were mapped. Modeling of correlations found positive associations with population density and a weak negative correlation with median income. The analysis was assessed and future work on this type of data was considered.

Spatial ecology of feral cats on San Clemente Island

Bridges, A. S., Sanchez, J. N., & Biteman, D. S. (2015). Spatial ecology of invasive feral cats on San Clemente Island: implications for control and management. Journal of Mammalogy, 96(1), 81-89.

Feral cats, Felis catus, inhabiting San Clemente Island, California, are both predators and competitors of multiple sympatric endemic species. To improve our understanding and management of these invasive predators, we used GPS-equipped radiocollars to track 11 (6F:5M) cats for a total of 3,108 days, resulting in 15,419 GPS locations. Average 100% minimum convex polygon, 95% kernel density, and 50% kernel density estimates were 229, 132, and 33 ha, respectively. The point estimate for average male home-range size was larger than the average for females, but there was substantial variation among individuals of both sexes. Overlap indices indicated similar usage areas during nocturnal and diurnal time periods. Sample size limited our ability to definitively detect habitat preference, but data suggested areas within 50 m of roads were avoided, and that thicker land cover was preferred over open grasslands. Three test collars deployed within active cat home ranges indicated GPS locations were precise, with 96% of locations having < 10-m error estimates, and that horizontal dilution of precision indices were not useful in screening data. Our results describe feral cat spatial ecology on a semiarid island and can be used to inform population estimation, control, and mitigation programs.

Feral cat eradication in the presence of endemic San Nicolas Island foxes

Hanson, C. C., Jolley, W. J., Smith, G., Garcelon, D. K., Keitt, B. S., Little, A. E., & Campbell, K. J. (2014). Feral cat eradication in the presence of endemic San Nicolas Island foxes. Biological Invasions, 1-10.

Projects to eradicate invasive species from islands are a high priority for conservation. Here we describe the process used to successfully eradicate an introduced carnivore on an island where a native carnivore of similar size was also present. We primarily used padded leg-hold live trapping to capture feral cats (Felis silvestris catus). Trapped feral cats were transported off-island and housed in a permanent enclosure on the continent. We used additional methods, such as tracking dogs and spotlight hunting, to detect and remove more-difficult individuals. Project implementation caused no significant negative impacts to the endemic San Nicolas Island fox (Urocyon littoralis dickey) population. Mitigation measures included on-site veterinary resources, modified padded leg-hold live traps, conditioned trap aversion, a trap monitoring system and personnel training. To confirm eradication, we utilized camera traps and sign search data in a model to predict project success. A key part of the success of this project was the partnerships formed between NGOs, and government organizations. With support from the partnership, the use of innovative technology to improve traditional trapping methods allowed feral cats to be removed effectively in the presence of a native species occupying a similar niche. This project shows that strong partnerships, innovative methods, and use of technology can provide the conditions to eradicate invasive species when major barriers to success exist.

Human and dog disturbance to shorebirds

McCrary, M. D., & Pierson, M. O. (2000). Influence of human activity on shorebird beach use in Ventura County, California. In Proceedings of the fifth California Islands symposium (pp. 424-427).

We studied the potential influence of human and dog activity on shorebird abundance at 13 sandy beaches in Ventura County, California. The 13 study beaches were randomly selected, and each beach was 1 km long. From June 1994 to May 1997, we counted all shorebirds, humans and dogs at each beach once per month for a total of 36 counts. We found no significant relationship between instantaneous counts of either shorebirds and human or dogs. However, there was a significant relationship among the 13 beaches between total shorebird and human use. The beaches with the greatest number of shorebirds (Ormond Beaches 1 through 3) were among those with the lowest number of humans. The results suggest that inaccessibility to humans may be an important aspect of shorebird habitat quality. Relatively undisturbed sandy beaches are quite rare in southern California, and the inaccessibility of the few remaining undisturbed beaches should be maintained. 

Dogs disturbing wintering plovers

Lafferty, K. D. (2001). Disturbance to wintering western snowy plovers.Biological Conservation, 101(3), 315-325.

In order to better understand the nature of disturbances to wintering snowy plovers, I observed snowy plovers and activities that might disturb them at a beach near Devereux Slough in Santa Barbara, California, USA. Disturbance (activity that caused plovers to move or fly) to wintering populations of threatened western snowy plovers was 16 times higher at a public beach than at protected beaches. Wintering plovers reacted to disturbance at half the distance (∼40 m) as has been reported for breeding snowy plovers (∼80 m). Humans, dogs, crows and other birds were the main sources of disturbance on the public beach, and each snowy plover was disturbed, on average, once every 27 weekend min and once every 43 weekday min. Dogs off leash were a disproportionate source of disturbance. Plovers were more likely to fly from dogs, horses and crows than from humans and other shorebirds. Plovers were less abundant near trail heads. Over short time scales, plovers did not acclimate to or successfully find refuge from disturbance. Feeding rates declined with increased human activity. I used data from these observations to parameterize a model that predicted rates of disturbance given various management actions. The model found that prohibiting dogs and a 30 m buffer zone surrounding a 400 m stretch of beach provided the most protection for plovers for the least amount of impact to beach recreation.

Toxoplasmosis risk to sea-otters

Seventeen percent of sea otters die from brain disease caused by a single-cell deadly parasite, Toxoplasma gondii. For eons, this parasite has moved mostly without notice among animals, including humans, on land. But now, it is migrating to the sea, where it is infecting mammals, including sea otters, whose immune systems are unprepared for the assault.

Toxoplasmosis and sea otters

Parasite Shed in Cat Feces Kills Sea Otters

Conrad, P. (2007). Parasite Shed in Cat Feces Kills Sea Otters. Healthy Marine Ecosystems • November 2006

Endangered sea otters in California have been found to suffer lethal infections from a parasite, Toxoplasma gondii, shed in cat feces. These infections may be a factor contributing to the marine mammal’s slow recovery from near extinction.

Toxoplasma gondii is a protozoan parasite that attacks an otter’s brain tissue, causing lesions, depression, convulsions and death.

Because cats are the only animals known to shed Toxoplasma gondii, runoff must be carrying cat feces and the parasite to the coast. From there, it is not clear how otters are getting sick. One possibility is that they are ingesting infected mussels or other filter-feeding bivalves, which accumulate pathogens in their tissues.

The parasite is usually harmless to healthy people. The exception is pregnant women, whose fetuses can develop toxoplasmosis, hence the advice for pregnant women to avoid cleaning cat litter boxes.

Once numbering more than 300,000, southern sea otters were hunted to near extinction in the 19th century for their lush pelts. They were granted protection under the Endangered Species Act in 1977, when their numbers were about 1,789. In the mid-1990s, their recovery staggered and concerns were raised about the animal’s long-term prospects. More recently their numbers seem to be rising.

Observers tallied a total of 2,692 California sea otters for the 2006 spring survey, compared with 2,100 in 2002 and 2,377 in 1995.

Feeding cats deplates native fauna

Hawkins, C.C., W.E. Grant & M.T. Longnecker. 1999. Effect of subsidized house cats on California birds and rodents. Transactions of the Western Section of The Wildlife Society, 35: 29-33

Cat advocates are establishing feeding stations in public parks, often claiming that well-fed cats pose little threat to wildlife. This claim was tested east of San Francisco, California, in a cat area and a no-cat area. In 1995, more harvest mice were trapped in the no-cat area. In 1996, more harvest mice (Reithrodontomys megalotis) and deer mice (Peromyscus sp.) were trapped in the no-cat area, and more house mice were trapped in the cat area. The numbers of trapped California meadow voles (Microtus californicus) were not different between the areas in either year. More native rodents were trapped in the no-cat area. Birds present during the breeding season were seen more often in the no-cat area. California quail (Callipepla californicus) and California thrashers (Toxostoma redivivum) were present in the no-cat area and absent in the cat area. Cats at artificially high densities, sustained by supplementary feeding, reduced the abundance or native rodent and bird populations, changed the rodent species composition, and may have facilitated the expansion of the house mouse into new areas. Thus we recommend that the feeding of cats in parks should be strictly prohibited. 

Mandatory spay ordinance as the solution to San Francisco dog problem

Lang, D. (2013). A Mandatory Spay/Neuter Ordinance in San Francisco: The Solution to San Francisco’s Other Homeless Problem. Master's Capstone Projects.Paper 6. University of San Francisco

The dog overpopulation in San Francisco has been straining San Francisco’s Department of Animal Care & Control’s already limited resources with the increase in dog impoundments and animal cruelty cases, particularly ones involving dogs. At least 33 local governments around the United States have implemented mandatory spay/neuter laws for all dogs as a way to curb the companion animal overpopulation. San Francisco should adopt a similar mandatory spay/neuter law, in which all dogs over the age of six months, with certain exceptions, must be spayed or neutered. This will relieve the strain on Animal Care & Control, will save the City money, and will decrease pain, suffering, and even death among San Francisco’s dog population.

Humans have a responsibility to care for companion animals because we domesticated them and allow them to breed in a world where there are not enough homes for them. So humans should take action to decease breeding, especially accidental breeding, so as to decrease the population of unwanted dogs. This human action should be in the form of implementing a mandatory spay/neuter law, so the majority of dogs will be unable to reproduce and so that breeders are restricted to one litter per year to minimize their contribution to the companion animal overpopulation. Not only is spaying and neutering crucial to reducing the population of unwanted dogs, but it also has many health, behavioral, and societal benefits. Spaying and neutering will increase the health of dogs by reducing their chances of developing certain cancers; it will increase their life span; and it will increase public safety and public health byreducing aggression, making them less likely to bite, and reducing the number of stray dogs wandering the streets.

Even though most veterinarians, most members of the animal shelter community, and most animal welfare/rights activists agree that spaying/neutering is vital to decreasing the companion animal overpopulation, they disagree on whether spaying/neutering should be mandatory or simply encouraged. Proponents of mandatory spay/neuter laws argue that they will save local governments money, produce more revenue, and improve public safety and public health. On the other hand, opponents argue that low-cost spay/neuter programs are more effective at decreasing the companion animal overpopulation, mandatory spay/neuter laws punish poor people and will result in more companion animals being abandoned in shelters, they discourage people from taking their animals to the vet or to the animal shelter for fear of being reported to authorities for having an unaltered animal, they punish responsible companion animal guardians and breeders, they waste public resources, and they are difficult to enforce.

An analysis of shelter data from two municipalities—Clark County, Nevada, and Los Angeles County, California—that have implemented mandatory spay/neuter laws reveals that recent dog intake and euthanasia rates are the lowest they have been in the past two decades, indicating that these laws are successful at reducing the unwanted dog population. In 2005, San Francisco’s Commission of Animal Control and Welfare considered implementing a mandatory spay/neuter ordinance for all dogs, but it never went past Commission meetings. However, in 2006, San Francisco implemented a mandatory spay/neuter law for Pit Bulls, which resulted in a decrease in Pit Bull euthanasia rates. The success of this law can be partly attributed to the free spay/neuter services for Pit Bulls offered by the San Francisco Society for the Prevention of Cruelty to Animals (SF SPCA). Other free spay/neuter services for any breed of dog are also offered in various locations in San Francisco, which would help ensure the success of a mandatory spay/neuter ordinance for all dogs.

San Francisco should implement a mandatory spay/neuter ordinance that requires that all dogs six months or older must be spayed or neutered, with exemptions for dogs who are too old or sick to undergo the spay/neuter surgery and dogs whose health would be threatened by the spay/neuter surgery. In addition, guardians who do not want to spay or neuter their dogs must obtain an intact dog license or a breeding license. Animal Care & Control can enforce the mandatory spay/neuter law by modifying its dog licensing system to assign different colored tags for different licenses—regular dog licenses, intake dog license, and breeding license.

Furthermore, breeders must show proof that they have a breeding license by putting the license number on their advertisements or sales receipts, and they must be restricted to one litter per year and the number of unaltered animals they are allowed to have should be limited, as well, so as to not further contribute to the companion animal overpopulation problem. And finally, penalties for violations of the mandatory spay/neuter law should be civil, rather than criminal.

Cats' threat to wildlife in San Diego County

(from http://www.utsandiego.com)

...In San Diego County, the potential threat feral cats pose to wildlife is particularly troublesome. Our county is within one of the world’s biodiversity hot spots. Our ocean, beaches, bays, mountains and desert landscapes, and unique coastal sage scrub and chaparral plant communities, support a wide diversity of plant and animal life, including more than 500 species of birds.

San Diego County is home to more endangered species than any other county in the nation.

Many of these species exist in small islands of habitat surrounded by urban development. At the edges of these small habitat patches, urban predators — animals that thrive in developed landscapes and prey on native species — pose a significant threat to their survival. Some of the urban predators that disturb or kill sensitive bird species in our county include crows, ravens, raccoons, opossums, rats — and feral cats.

One example of this situation can be found at the Kendall-Frost Marsh in Mission Bay. The marsh is home to a population of federal- and state-listed endangered light-footed clapper rails, a secretive bird that relies on coastal wetland habitats. Urban predators are trapped in the marsh as part of management efforts to protect clapper rails. Feral cats have been trapped at the marsh and brought to San Diego County’s animal shelter. This co-occurrence of feral cats and light-footed clapper rails creates the possibility of a predation problem. Biologists who monitor this species counted fewer than 600 breeding pairs in 2013. Predation of even a few of these birds may have a significant effect on the species’ ability to recover to stable population numbers in the marsh....

Feral dogs as potential threat for pinnipeds

García-Aguilar, M.C. & J.P. Gallo-Reynoso 2012. Feral dogs at Isla de Cedros, Baja California, Mexico: a possible threat for pinnipeds. . Revista Mexicana de Biodiversidad, 83 (3): 785-789.

The presence of feral dogs (Canis lupus familiaris) in Isla de Cedros, Baja California, Mexico, has been documented for over 15 years. In the summer of 2009 and the winter of 2009/2010, 2 sampling surveys were conducted in the northeast coastal portion of the island to assess the diet of feral dogs in the vicinity of hauled out California sea lions (Zalophus californianus) and northern elephant seals (Mirounga angustirostris). Mammals were the most important prey group in the diet of dogs (85.4%). Our results show that in the northeast coast of Isla de Cedros, feral dogs feed on pinnipeds: the elephant seal was the most important prey in both seasons (43.3% in summer and 51.9% in winter), followed by the sea lion as the second most important prey during the summer (23.3%), while its importance decreased in the winter (5.8%). Besides the potential predatory activity, there is an important likelihood that pinnipeds could be infected by pathogens of dogs, with serious epizootic consequences.


García-Aguilar, M.C. & J.P. Gallo-Reynoso 2012. Perros ferales en la isla de Cedros, Baja California, México: una posible amenaza para los pinnípedos. Revista Mexicana de Biodiversidad, 83 (3): 785-789.

La presencia de perros ferales (Canis lupus familiaris) en la isla de Cedros, Baja California, México, fue documentada hace más de 15 años. En el verano de 2009 e invierno 2009/2010, se realizaron 2 campañas de muestreo en la costa noreste de la isla para evaluar los hábitos alimentarios de los perros en las cercanías de las zonas de reproducción y descanso del lobo marino de California (Zalophus californianus) y del elefante marino del norte (Mirounga angustirostris). Los mamíferos constituyeron el grupo consumido más importante en la alimentación de los perros (85.4%). Los resultados de este estudio muestran que en la costa noreste de la isla de Cedros los perros se alimentan de pinnípedos: el elefante marino fue la especie que más se consumió, con el mayor porcentaje en ambas temporadas (43.3% en verano y 51.9% en invierno); el lobo marino, fue la segunda durante el verano (23.3%), aunque su porcentaje disminuyó en el invierno (5.8%). Además del potencial impacto que el consumo por los perros pueda tener sobre las poblaciones de los pinnípedos, una amenaza adicional es la posible transmisión de los patógenos caninos, con serias consecuencias epizoóticas.

Monitoring feral dog’s population at Isla de Cedros

García-Aguilar, M.C. 2012. Monitoring feral dog’s population at Isla de Cedros, Baja California, and the associated threats over native mastofauna. Acta Zoológica Mexicana (n. s.), 28(1): 37-48.

Monitoring introduced species is an important management tool in order to preserve native species. The aim of this study was to monitor the feral dog’s population in Isla de Cedros and to identify actual and potential threats of their presence over the native mastofauna. Data were collected at two sampling areas of the island, the Northeast Coast (CNE) and the Central-South Region (RCS). Dog’s distribution pattern and density was assess using a non-invasive method based on scat counts along transect surveys and relative density (R) and faecal relative abundance index (fRAI) were estimated. Dog’s diet composition was evaluated by scat analysis. Both R and fRAI were significant greater (P < 0.05) in the CNE than in the RCS. The results showed that feral dogs are feeding from at least three endemic terrestrial mammal species (the mule deer, the brush rabbit, and the Anthony’s pocket mouse) and two pinnipeds species (the northern elephant seal and the California sea lion). With this study provide a useful baseline for future comparison and monitoring and control purposes. Nevertheless, it is necessary to conduct studies about the dog’s feeding behavior to measure their predatory activity and to assess the associated damage level. Also, due to the fact that interactions between dogs and pinnipeds appeared frequently and because they are phylogenetically related, the greatest threat of the dog’s presence is that it could be a disease vector, with serious health outcomes for the wildlife.


García-Aguilar, M. C. 2012. Monitoreo de la población de perros ferales en la Isla de Cedros, Baja California, y las amenazas a la mastofauna nativa. Acta Zoológica Mexicana (n. s.), 28(1): 37-48.

El monitoreo de especies introducidas es una herramienta importante para preservar las especies nativas. El objetivo de este estudio fue monitorear a la población de perros ferales en la Isla de Cedros e identificar las amenazas actuales y potenciales de su presencia sobre la mastofauna nativa. La colecta de datos se realizó en dos áreas de la isla, la costa noreste (CNE) y la región centro-sur (RCS). Los patrones de distribución y la densidad de los perros se determinaron con un método no invasivo basado en el conteo de excretas a lo largo de transectos y se estimó la densidad relativa (R) y el índice de abundancia relativa fecal (fRAI). La composición de la dieta se evaluó por medio del análisis de las excretas. Tanto los valores de R como de fRAI fueron significativamente mayores (P < 0.05) en CNE que en RCS. Los resultados mostraron que los perros se alimentan de al menos tres especies de mamíferos endémicos (el venado bura, el conejo matorralero y el ratón de abazones de Cedros) y de dos especies de pinnípedos (el elefante marino del norte y el lobo marino de California). A partir de este estudio se cuenta con una línea de base que podrá ser usada en los programas de control y monitoreo futuros. Sin embargo, es necesario desarrollar estudios sobre el comportamiento alimentario de los perros para evaluar su actividad predatoria y medir el nivel de daño asociado; además, dado que las interacciones entre pinnípedos y perros parecen ser frecuentes y están relacionados filogenéticamente, posiblemente la mayor amenaza de la presencia de los perros sea la propagación de enfermedades infeccionas, con graves resultados para la vida silvestre.

Biology and ecology of feral, free-roaming, and stray cats in California

Ogan, C. V., & Jurek, R. M. (1997). Biology and ecology of feral, free-roaming, and stray cats. In Mesocarnivores of northern California: biology, management, and survey techniques, workshop manual (pp. 87-92).

No abstract available. Click for full-text

Home range of neutered cats

Guttilla, D. A., & Stapp, P. (2010). Effects of sterilization on movements of feral cats at a wildland-urban interface. Journal of Mammalogy, 91(2), 482-489.

Trap–neuter–release (TNR) programs, in which feral cats are sterilized and fed in unconfined colonies, have been advocated as a humane and effective way to reduce the impacts of feral cats on native wildlife. Little is known, however, about the effects of sterilization on feral cat movements and space use, particularly where colonies are located near natural areas. We determined home-range area and overlap and characterized the long-range movements of 14 sterilized and 13 intact radiocollared cats on Catalina Island, California, from 2002 to 2004. Male home ranges were significantly larger than those of females, but no significant differences were revealed in home-range areas or overlap between sterilized and intact cats. Cats regularly moved between natural habitats in the interior of the island and human-populated areas regardless of sex or treatment status, although most (68%; 17/25) of the cats that moved long distances were female. Island-wide, the cat population was estimated to be 600–750 cats, with >70% associated with developed areas, including existing TNR colonies. The influx of subsidized cats to natural habitats, combined with their high vagility and low trappability, makes TNR an unlikely solution for controlling feral cats on a large, rugged island like Catalina and, more generally, in other locations where human populations abut ecologically sensitive areas.

Spatial organization and habitat use of feral cats in California

Hall, L. S., Kasparian, M. A., Van Vuren, D., & Kelt, D. A. (2000). Spatial organization and habitat use of feral cats (Felis catus L.) in Mediterranean California. Mammalia, 64(1), 19-28.

We report on a preliminary study of the spatial organization, habitat use, and diet of feral cants (Felis catus) in a riparian reserve in Central California, to assess potential impacts of this exotic predator on native species. Home ranges of adult cats averaged 31,7 ha and did not differ significantly by sex and season. Home ranges also showed little overlap, suggesting a territorial social system. Cats strongly preferred riparian habitats and foraged primarily on native species of small mammals, especially California voles (Microtus californicus) and Botta's pocket gophers (Thomomys bottae), although birds, insects, and exotic rodents were also eaten. The preference for riparian habitats and native preys suggests that impacts on biodiversity by feral cats may be great, especially in Mediterranean climates where riparian communities already are heavily impacted by urbanisation and agriculture.