By Hunter Peters
In the United States, we have invested significant government resources toward the control of invasive species populations, with the aim of reducing their impact on native species. But there is one invasive species that has largely avoided this level of government investment and public attention: the domestic cat. For cat lovers in particular, the idea of cats being an invasive species probably borders on offensive (full disclosure: I’m really more of a dog person.)
However we may feel, though, the fact remains that cats are not native to the United States, and as birdwatcher Noah Strycker puts it, in order to find a “more successful” invasive species, “you’ll need a mirror.”
According to genetic analysis from a study cited by journalist David Zax in his article, “A Brief History of Cats,” the domestic cat (Felis cata) was first domesticated from Middle Eastern wildcats (Felis sylvestris) in the Middle East’s Fertile Crescent approximately 12,000 years ago, around the time when the first agricultural civilizations were formed. From here, domestic cats spread to Europe alongside humankind as humans formed new civilizations there, and when humans began to sail to new continents during the Age of Exploration cats would join them aboard these voyages as well.
The global population of cats, now sitting at half a billion, eventually spread across six continents and 118 main island groups out of 131, according to Strycker’s article, “Cat vs. Bird: The Battle Lines.” Because native species in these locations did not evolve alongside domestic cats they are particularly vulnerable to cat predation, and their negative effect on biodiversity has placed domestic cats among the 100 most harmful invasive species in the world, according to Scott Loss, Tom Will, and Peter Marra. In addition, feral cats act as a natural reservoir for zoonotic diseases, diseases capable of being transmitted from a nonhuman animal to humans, including rabies, Toxoplasma gondii, tularemia, and even plague, according to R.W. Gerhold and D. A. Jessup’s study, “Zoonotic Diseases Associated with Free-Roaming Cats.”
Impact of Feral Cats
Previous estimates of the impact of domestic cats on native species might have actually underestimated the rate of animal mortality, according to a systematic review of existing studies conducted by Scott Loss, Tom Will, and Peter Marra titled, “The impact of free-ranging domestic cats on wildlife of the United States.” According to the authors, free-roaming cats, including both owned and unowned feral cats may, “exceed all other sources of anthropogenic mortality of US birds and mammals.” Loss, Will, and Marra found that free-ranging cats kill between 1.3 and 4 billion birds, along with 6.3 to 22.3 billion small mammals each year in the United States.
For Australia in particular, feral cats represent a dire threat to native species. Jessica Camille Aguirre wrote an article for The New York Times in April 2019 titled “Australia Is Deadly Serious About Killing Millions of Cats,” which documented how the Australian government had undertaken a regular culling of feral cats in order to mitigate their impact on native species. The article described how officials airdropped poisoned sausages over feral cat colonies, using a poison from a plant that is only lethal to nonnative species. Aguirre’s article in turn prompted me to begin researching how feral cats are affecting native species in New York State, and whether a feral cat culling could be replicated here.
Unfortunately, after reaching out to a representative of the New York State Department of Environmental Conservation (DEC), I was informed that the DEC had not conducted any studies into feral cat predation in New York. The representative did tell me, however, that the DEC “acknowledges that feral cats have negative impacts on birds of concern in the state,” and that the DEC has employed “education and outreach” to encourage “cat owners and advocates to keep their companions indoors.” The primary reason that the DEC has not undertaken research specific to New York is that feral cats are not legally considered wildlife under New York law, as all domestic cats, regardless of whether they are owned or unowned, enjoy protected status as companion animals under sections 353 and 353-A of the Agriculture and Markets Law.
Population Control Measures
The protected status that feral cats enjoy in New York would obviously pose a legal obstacle for any culling as potentially indiscriminate as that used in Australia. The revelation, however, raised new questions on whether alternative measures may exist for controlling feral cat colonies, short of airdropping poison sausages. From my research, I learned that other states have implemented two types of programs aimed at controlling feral cats: trap and euthanize programs, which are a form of strategic culling; and Trap-Neuter-Return (TNR) programs, which involve front line workers trapping members of feral cat colonies, vaccinating them to deter the spread of zoonotic diseases, neutering them to slow the growth of the colony, and then returning them to the location in which they were found. According to Loss, Will, and Marra, TNR programs are implemented widely across the United States, despite their potential harm to native species and the fact that legislators do not typically undertake a review of the program’s environmental impact. Part of the reason for this lack of scientific consideration is that animal advocacy organizations possess extensive influence in the United States and can successfully lobby State Legislatures, while according to Aguirre such groups are comparatively weak in Australia.
In New York, the State Government has left a status quo in which feral cat populations have gone both understudied and uncontrolled, with neither a TNR or trap and euthanize program implemented at the state level. Nonetheless, I wondered whether front line workers, such as Forest Rangers, could exercise discretion in their approach to feral cat colonies. For this, I reached out to Mike Bodnar, a now retired New York State Forest Ranger, to learn how Forest Rangers approach the state’s feral cat population. Bodnar told me that because feral cats enjoy legal protection as companion animals in New York, he was only authorized to kill a feral cat if he personally witnessed one attacking a member of a threatened or endangered species while on patrol. And while Bodnar recognized that the State Government has not actively sought to control the feral cat population, he pointed out that coyotes and fishers prey on feral cats and that some are killed by automobiles, providing at least some negative pressure on their population.
While New York may not have implemented a TNR or trap and euthanize program, in 2015 the State Legislature did attempt to pass a law that would have essentially created a statewide TNR program, a measure supported animal welfare organizations. According to an article by Jon Campbell titled “Feral cat bill claws way through New York State Legislature,” the State Legislature put forward a bill that would have enabled the State’s Animal Population Control Program to direct up to 20% of its funds, which are collected from dog licensing fees, toward nonprofits that would then administer TNR programs across the state. The legislation was opposed by an unlikely coalition, most prominently the New York Sportsmen’s Advisory Council and People for the Ethical Treatment of Animals (PETA). After the State Senate passed the bill these groups successfully lobbied Governor Andrew Cuomo to veto it. Cuomo justified his veto by casting doubt on the effectiveness of TNR programs, explaining in a statement that “prevailing science suggests [TNR] programs are not guaranteed to reduce feral cat populations, and, even if they do, may take many more years to do so than existing programs.”
Among the prevailing science that has questioned the effectiveness of TNR programs is a cost-benefit analysis conducted by Cheryl Lohr, Linda Cox, and Christopher Lepczyk in 2013 titled “Costs and benefits of trap-neuter-release and euthanasia for removal of urban cats in Oahu, Hawaii,” which modeled out changes in a feral cat colony over 30 years. In terms of effectiveness, the TNR program took the full 30 years to fully eradicate the colony, while the trap and euthanize program was able to eradicate the colony by its second year in 75% of the simulations, so long as the colony’s population remained stable. However, when the simulation increased the population of the colony by 10% each year, the trap and euthanize program could not prevent the colony from returning to carrying capacity within 6 years, while the TNR program was unable to eradicate the colony even within these 30 years. In terms of cost, TNR was twice as expensive as the trap and euthanize program.
Another study from Billie Lazenby, Nicholas Mooney, and Christopher Dickman, titled “Effects of low-level culling of feral cats in open populations: a case study from the forests of southern Tasmania,” focused on the effectiveness of less intensive culling programs used in some countries. The authors found that the number of cats at the two sites they studied actually increased during the 13-month period of observation by 211% and 75%, while the population remained stable at the control site where no trapping was conducted. The most likely explanation for the low-level culling’s counterproductive effect on feral cats, according to the authors, was that the removal of dominant feral cats enabled subordinate cats, which had previously been excluded from the site of the colony, to take up residence within the colony. Two alterative explanations were that the experiment’s culling was not sufficiently intense or that the culling removed dominant cats from the colony, freeing up resources for other members of the colony and allowing their offspring a greater chance of surviving.
In New York, even a modest low-level culling would likely require an amendment to the Agriculture and Markets Law, in order to signal to state agencies that feral cats are wildlife suitable for research and population control, rather than companion animals. If the State Legislature found the political impetus to pass such an amendment while also designating state funds for a trap and euthanize program, then it would be prudent to implement an accompanying monitoring program and an education program discouraging cat owners to from abandoning their animals. Perhaps the most immediate measure to address feral cats in New York, however, would involve a study, administered either by a state agency or university researchers, to measure feral cat predation. If members of the public are made aware of the impact that feral cats can have on threatened species they are already familiar with seeing at their birdfeeders or around their lawns, then perhaps even cat lovers can recognize the urgency of feral cat population control.
Photo Source: Shutterstock, “forestpath.”
Hunter Peters is a writer from Washington County, who is studying International Affairs at Rockefeller College of Public Affairs and Policy.