Evaluation of a trap-neuter-return management program for feral cat colonies: Population dynamics, home ranges, and potentially zoonotic diseases
Publication Type: |
Thesis |
Year of Publication: |
2005 |
Authors: |
Felicia B. Nutter |
Publication/Journal: |
Comparative Biomedical Sciences |
Publisher: |
North Carolina State University |
Keywords: |
cat, dissertation/thesis, feral cats, trap-neuter-return, zoonotic diseases |
Abstract:
With this research project I evaluated the effectiveness of trap-neuter-return management for feral cat colonies, and specifically examined the prevalence of selected infectious diseases, population dynamics, and home ranges for feral cats under different management strategies. I used an effective trapping method and captured 98% of the target cats with 8.9 trap nights per cat. Breeding female cats produced a mean of 1.4 litters per year, with a mean of 3 kittens per litter. The majority of kittens (75%) died or disappeared by 6 months of age, and trauma was the most common cause of death. Pregnancies occurred throughout the year but peaked between March and May. I showed that feral cats and pet domestic cats had similar baseline health status and fecal prevalences of infections with Cryptosporidium spp., Giardia spp. and Toxocara cati. Feral cats had higher seroprevalences of Bartonella henselae and Toxoplasma gondii, and these findings are likely related to greater exposure of feral cats to the vectors or hosts of these organisms. Survival analysis of individual intact and neutered cats in 9 colonies showed that castrated male cats and ovariohysterectomized female cats live significantly longer than their breeding counterparts, or than vasectomized males. Colonies managed by trapneuter-return were stable in composition and declining in size throughout the seven year follow-up period. On average, breeding control colonies increased in size and had high turnover of cats, although one colony did experience a population crash followed by a rebound. Immigration into both breeding and sterilized colonies was consistent but occurred at low levels. One sterilized colony went extinct after 31 months of follow-up, and the several other colonies consisted of 5 or fewer cats after 7 years of follow-up. The two most common outcomes for individual cats were disappearance from the colony or death, most often due to trauma. Vasectomized male cats were more likely to be killed by vehicles than intact or castrated males. The home ranges of the managed feral cats were small, usually less than 1 hectare, regardless of sex or reproductive status. Vasectomized male cats had significantly larger home ranges than intact or castrated male cats, but the sizes of intact and castrated male cat home ranges were similar, as were the home ranges of intact and spayed female cats. Vasectomized males moved significantly greater distances from the feeding sites than intact or castrated males, and spayed females moved farther than intact females though the difference for females may not be biologically important. The larger home range size and greater distance moved from feeding sites for vasectomized male cats are likely related to their search for breeding females, since the females in their home colonies were spayed. Community-level stakeholder meetings were successful in fostering consensus among participants with different backgrounds, preferences and agendas, and the need for multiple feral cat management options to address a diversity of situations was recognized. I used the data generated during the monitoring phase of this project to set up and run a population viability analysis model with VORTEX 9.57 software. I simulated the potential fates of intact breeding colonies subjected to various harvest levels and harvest intervals, and of sterilized colonies with different proportions of breeding adults. The models suggested that harvesting breeding colonies every one or two years at very high levels can keep colonies small, but will not lead to long-term reduction in the numbers of cats because colonies can re-establish due to immigration. The models of neutered colonies suggested that sterilization levels of at least 75% to 80% are necessary to cause population decline and eventual colony extinction, assuming that immigrant cats are also sterilized. The mean estimated time to extinction of 12.8 years fits well with ongoing observations of steady decline in the colonies managed by trap-neuter-return. Overall, the trap-neuter-return strategy is effective and provides a viable option for feral cat management.