Cats, Native Species, And Impact Mitigation
Cats are one of the most beloved companion animals, and as a result, one of the most widespread. Because they are effective hunters and receive benefits from humans such as veterinary care and food, domestic cats are much more numerous than a similarly sized predator would be without human intervention. This means cats have a unique ability to impact native wildlife. This is not a new observation, but the size and scope of the impact have only recently been quantified.
All feral cats hunt, as well as most companion cats who are allowed outside. Cats may hunt a variety of small animals including birds, mammals, and amphibians. According to some studies, it’s estimated that cats kill 1 billion birds per year in the U.S. alone. It’s also believed that cats are a contributor to 63 modern extinctions among birds, mammals, and reptiles. It’s worth mentioning here that these numbers are estimates, and the estimates can vary quite widely.
In addition to the impacts of their hunting, cats influence native species through fear, hybridization, and competition. The effect of fear is harder to quantify, but evidence suggests that surprisingly, it may be more impactful than hunting. One study showed that briefly placing taxidermied cats near blackbird nests reduced the amount parents fed their young by a third.
In this paper, the authors discuss several approaches to mitigating the impact of cats on native species. Interventions such as anti-predation bells, curfews, vaccination, or limiting the number of cats per guardian are effective to some extent, but none are effective in all contexts or with all native species.
The authors take European Union nature conservation legislation (called the Nature Directives) as a specific example of legislation that seems to require the member states to address the effects of domestic cats on native species. The nature directives include two obligations: the first is to regulate the introduction of non-native species, and the second is to maintain the populations of wild bird species.
Court rulings on similar cases have made it clear that the obligation is measured by outcome, not by effort — and it applies even if the harm existed already. Specifically, the protection of wild birds means that they cannot be deliberately killed or captured, or their eggs disturbed or destroyed. There’s ambiguity around the use of the word “deliberate,” but test cases around another protected species, loggerhead sea turtles, have made it clear that “deliberate” does not have to mean “intentional” — it means that the activity occurred despite the possibility of disturbing or killing native birds.
Following this argument, even though allowing one’s cat outside is probably not intended to harm protected wildlife, the law implies that there should not be free-ranging cats in the E.U. So why hasn’t this been done? The authors point to these reasons in particular:
- Authorities may not be aware of the issue or may interpret the state’s responsibility differently
- It might be considered infeasible to restrict cats or cat guardians in this way
- Politicians may fear the political unpopularity among cat guardians or animal advocates.
The authors conclude that restricting domestic cats is an area where a large impact can be made in preserving biodiversity. However, the cost will be the populations of stray and feral cats currently largely accepted in the E.U., and the freedom of cat guardians to let their companion cats roam. The proposed harm reduction measures – such as trap-neuter-vaccinate-return programs and anti-predation measures – could suggest a middle ground where animal advocates and those primarily concerned with native bird populations can agree.