# Evaluating the Effects of Managed Free-Roaming Cat Populations on Prey Through Stable Isotope Analysis: A Pilot Study from British Columbia, Canada

## TL;DR

This study shows that trap-neuter-return (TNR) programs with food provisioning can reduce free-roaming cats' reliance on wild prey, helping protect biodiversity.

## Contribution

The study demonstrates that TNR with food provisioning reduces free-roaming cats' consumption of wild prey using stable isotope analysis.

## Key findings

- Cats under TNR with food provisioning showed diets similar to indoor cats, relying on commercial food.
- Isotopic analysis revealed reduced reliance on wild prey and raw mink feed after TNR implementation.
- Dietary shifts were consistent with decreased consumption of wildlife following TNR and mink-farm closure.

## Abstract

Free-roaming domestic cats can affect biodiversity through their consumption of wild prey, creating challenges for both wildlife conservation and animal welfare. Trap-neuter-return (TNR) programs, which involve sterilizing and returning cats to their colonies, are increasingly used as a management approach and are often combined with regular food provisioning. However, it is uncertain whether these measures reduce reliance on prey in the diet. In this study, we investigated the diets of 122 cats on a rural property in Canada before and after the implementation of a TNR program with food provisioning and during the concurrent cessation of nearby mink-farming operations. By analyzing chemical markers in cat fur, we compared cats that lived indoors, cats before TNR, and cats after TNR with regular feeding. Before TNR, cats showed clear signs of consuming wild prey, while after TNR and food provisioning their diets shifted to resemble those of indoor cats, relying mostly on commercial food. These findings are consistent with a reduced dependence on wildlife and raw mink feed under the combined influence of TNR with food provisioning and the closure of mink operations. Our findings highlight the value of this management strategy for reducing ecological impacts of free-roaming cats while supporting humane population control.

Free-roaming domestic cats (Felis catus) present a major management challenge for animal welfare and biodiversity conservation. Trap-neuter-return (TNR) programs, which include sterilization and return of cats, are increasingly adopted to manage cat populations, often alongside routine food provisioning. However, their effectiveness in reducing cats’ reliance on wild prey remains contested. In this study, we use stable isotope analysis (δ13C, δ15N, δ34S) of cat fur to investigate dietary patterns before and after TNR implementation in the context of concurrent changes in food availability linked to the closure of nearby mink-farming operations. We analyzed samples from 122 cats in a large-scale TNR initiative on a rural property in British Columbia, Canada. These included indoor cats (control), free-roaming cats prior to TNR (Group 1), a subset of Group 1 re-sampled months after food provisioning began (Run 2), and newly sampled cats that had been fed regularly before trapping (Group 2). Local prey and food sources were also analyzed to provide a comparative isotopic baseline. Our results show clear dietary shifts following TNR. Group 1 cats exhibited high isotopic variability and elevated δ15N and δ34S values, consistent with wild prey consumption. In contrast, post-TNR cats showed significantly lower and more homogeneous values, aligning closely with those of indoor, kibble-fed cats. These changes are consistent with a reduced dietary reliance on wildlife and raw mink feed following the combination of TNR with regular provisioning and the cessation of mink operations. These findings demonstrate that regular food provisioning in TNR-managed colonies, particularly when combined with broader environmental changes, can significantly alter cat diets and potentially reduce their dependence on wild prey.