6/12/2006 1:50 PM Page 74 Outdoor fecal deposition by free-roaming cats and attitudes of cat owners and nonowners toward stray pets, wildlife, and water pollution SMALL ANIMALS Haydee A. Dabritz, BSc; E. Robert Atwill, DVM, PhD; Ian A. Gardner, BVSc, MPVM, PhD; Melissa A. Miller, DVM, PhD; Patricia A. Conrad, DVM, PhD ABBREVIATIONS Objective—To estimate cat population size, manage- CI Confidence interval ment, and outside fecal deposition and evaluate atti- MDFW Mean daily fecal weight tudes of cat owners and nonowners to stray animal TNR Trap-neuter-return control, water pollution, and wildlife protection. Design—Cross-sectional survey. of cats are acquired as strays2-7,10,11 and by population Sample Population—294 adult residents of Cayucos, models indicating that births among stray cats account Los Osos, and Morro Bay, Calif. for the difference between projected and observed rates 12 Procedures—Telephone survey. of change in population size. Results—The region’s cat population was estimated Although much attention has been focused on the at 7,284 owned and 2,046 feral cats, and 38% of sur- effect of free-roaming cats on wildlife, little considera- veyed households owned a mean of 1.9 cats/house- tion has been given to the contribution of owned and hold. Forty-four percent of cats defecated outside feral cats to fecal pollution. Results of several stud- > 75% of the time. Annual fecal deposition (wet ies13,14 suggest that pet feces contribute to bacterial weight) by owned cats in the 3 communities was esti- loading of streams and coastal waters. A study15 of mated to be 77.6 tonnes (76.4 tons). Cat owners were Escherichia coli ribotypes in Morro Bay, Calif, and its more likely to oppose cat licensing and impounding inflows reveals that 2.5% of all isolates are of felid ori- stray cats and support trap-neuter-return for stray cats gin, with a higher proportion (7.4%) from felids at the and less likely to be concerned about water pollution, Pismo Seep downstream from Los Osos. In the south- than were noncat owners. ern sea otter (Enhydra lutris nereis) range from Half Conclusions and Clinical Relevance—Feral cats rep- Moon Bay to Point Conception near Santa Barbara, resented a sizeable proportion (22%) of the free- Calif, Toxoplasma gondii, a protozoan parasite shed roaming cats in this area and could be contributing only in the feces of felids,16 caused 16% of southern sea 30.0 tonnes (29.5 tons) of feces to the environment 17 per year. However, feral cats are not the principal otter deaths that were evaluated from 1998 to 2001. source of fecal loading because owned cats defecat- Fifty-two percent of dead and 38% of live southern sea ing outdoors contribute an estimated 77.6 tonnes otters sampled from 1998 to 2004 were infected with (76.4 tons) or 72% of the annual outdoor fecal depo- T gondii.18 A study19 of risk factors for T gondii exposure sition. (J Am Vet Med Assoc 2006;229:74–81) in sea otters found that otters sampled near heavy freshwater outflows are 3 times as likely to be at risk for infection as otters sampled near low freshwater out- he owned cat population in the United States is flow. The most unexpected finding of that study19 was Testimated to be approximately 70.8 million, with that sea otters from the Morro Bay area are 9 times as 1 31.6% of households owning a cat. The feral cat pop- likely to be infected with T gondii as otters from any ulation represents an additional unknown number of other area on the central California coast. This finding cats, which could be sizable because 7% to 25% of suggests that, as a high-risk site, the Morro Bay area is households admit to feeding free-roaming cats and an ideal location for an ecological study of this zoonot- many thousands of cats are euthanized annually in 2-9 ic parasite, the first phase of which is the present study shelters. Other evidence for a large feral cat popula- of cat management and outdoor fecal deposition. tion is suggested by surveys indicating that 14% to 32% Although wild felids can shed T gondii oocysts in their feces, domestic cats are far more abundant than moun- From the Wildlife Health Center (Dabritz, Conrad) and Department of tain lions or bobcats in California coastal watersheds.20 Medicine and Epidemiology (Gardner), University of California, Domestic cats shed 3 to 349 million T gondii oocysts 3 Davis, CA 95616; Veterinary Medicine and Teaching Research Center, 18830 Rd 112, Tulare, CA 93274 (Atwill); and California Department to 5 days after consuming infected animal tissues, with of Fish and Game, Marine Wildlife Veterinary Care and Research a longer prepatent period when fed tachyzoites or Center, 1451 Shaffer Rd, Santa Cruz, CA 95060 (Miller). oocysts.21-25 Although oocyst shedding usually occurs Supported by the Wildlife Health Center at the University of after initial infection and lasts no longer than 3 weeks, California-Davis, the Schwall Medical Fellowship, National Science cats superinfected with Isospora felis, treated with large Foundation grant No. 0525765, and Morris Animal Foundation doses of corticosteroids, deprived of food, or reexposed grant No. D03ZO-25. to T gondii years after initial infection may shed oocysts The authors thank Jane Stevens, David Hird, Laurel Beckett, Janet 21,26,27 Foley, and Debbie Bee for technical assistance. again, albeit in lesser quantity. To our knowledge, Address correspondence to Dr. Conrad. no studies have attempted to quantify the contribution 74 Scientific Reports: Original Study JAVMA, Vol 229, No. 1, July 1, 2006 6/12/2006 1:50 PM Page 75 of cats to fecal loading in any area, despite the fact that Community households and area—The number of SMALL ANIMALS 40% to 88% of owned cats are allowed outdoors all or occupied households in each community was obtained from 31 part of the time and have ample opportunity to defe- Census 2000 data (Table 1). The area of each community cate outside.2,3,10,28 was determined by contacting the city engineer and obtain- The purposes of the study reported here were to esti- ing the area served by the urban reserve sewage line or future sewage line for Los Osos (Table 2). Total human population mate the owned and feral cat population size, establish in the 3 communities was 27,644 (Cayucos, 2,943; Los Osos, how owned cats were managed, estimate the amount of 14,351; and Morro Bay, 10,350) in an area of 11.5 miles2 fecal deposition into the environment caused by domes- (29.4 km2). Among the communities, the median age of res- tic cats, and determine the attitudes of cat owners versus idents ranged from 43 to 46 years, mean number of persons noncat owners with regard to stray pet management, per household ranged from 2.1 to 2.4, and median annual water pollution, and wildlife conservation. income in 1999 ranged from $34,400 to $46,600.31 Cat population—The mean number of cats per house- Materials and Methods hold in each community was calculated as the total number Telephone survey design—The telephone survey was of cats owned in the last 12 months divided by the number based on the 2002 to 2003 Estero Bay Community phone of households responding (adjusted to account for house- book published by Sun Bulletin of Morro Bay, Calif, and holders who stated they did not own cats and did not wish to included the communities of Cayucos, Los Osos, and Morro participate in the survey). Pet-owning households are more Bay. Business listings and duplicate listings for the same likely to respond to a survey about pet ownership,32 so the address were excluded from the sampling frame. The remain- adjustment was intended to reduce bias attributable to non- ing listings were counted, yielding 11,747 telephone num- response. The total cat population was calculated by taking bers. The telephone listings were not sorted by community the adjusted mean number of cats per household times the and were considered too large to stratify by community before number of occupied households as indicated in Census 2000. sampling. The required sample size of 323 was estimated on The variance for this estimator was calculated as follows: the basis of an AVMA estimate (95% CI) that 30% of US 29 households own cats. Because the proportion of cat-owning s2 N – n Variance = N2 households in each community was unknown and assumed to n X N be 30% for each of the 3 strata, a stratified sample size calcu- lation would yield a smaller sample size.30 From Census 2000 where N is the number of households, s2 is the sample variance data, households in Cayucos, Los Osos, and Morro Bay repre- for the mean number of cats per household, and n is the sam- sented 11.3%, 47.8%, and 40.9% of occupied households, ple size. Cat density for each community was estimated by respectively.31 Sampling based on proportional allocation dividing the cat population size by the community area in implied that if the target sample size of 323 was achieved, it hectares (1 hectare = 10,000 m2 or 2.47 acres). The feral cat should consist of 37 respondents from Cayucos, 154 from Los population was estimated by asking householders if they had Osos, and 132 from Morro Bay. The sample size was multi- fed a stray cat in the past month and, if so, how many. This plied by 4 to account for refusals to participate, and division methodology has been used in surveys from San Diego and of the listed telephone numbers by this value yielded a 1-in-9 Santa Clara Counties, California; Massachusetts; and Alachua systematic sample.