“The cat is the most harmful invasive predator for biodiversity.” This statement summarizes a recently published letter by a group of Spanish scientists criticizing gaps in the draft law on the protection, rights and welfare of animals. Approved by the government three months ago, the document argues that the bill clashes with European laws and strategies for biodiversity conservation. The researchers suggest a medium-term environmental goal that addresses wild cats and cat colonies.
The letter, published in Conservation Science and Practice, compiles findings from numerous studies on cats in recent years. Among the key points:
It states that pet cats contribute to more than a quarter of contemporary extinctions of birds, mammals and reptiles worldwide and are considered the most harmful invasive predators. Hunting by cats is described as the leading cause of death for small mammals and birds, with other threats including crossing predators, poisoning or predation by human hunters.
Contrary to popular belief, well-managed cat colonies still hunt wild prey, and due to their high density, feral cats often exert several times greater pressure on prey populations than domestic predators. The effects of cats are noted as particularly severe on islands, where the bill would complicate efforts to preserve endemic fauna in places like the Canary Islands and the Balearic Islands.
Beyond hunting, cats can act as vectors and reservoirs for numerous diseases that threaten wildlife and public health. Wild cat colonies may play a pivotal role in disease dynamics because of high density, frequent interactions within colonies, and contact with both owned and feral cats.
Criticism of the animal welfare bill
The letter opens by noting how moral circles have historically expanded to include nonhuman beings, leading to various legal instruments worldwide that grant rights to animals. It argues that such trends can influence policy design and conservation outcomes.
In a photo from the debate, a cat colony in a town illustrates the broader issue of how human attitudes toward animals shape policy and practice.
It is argued that including animals in moral circles is subject to biases toward charismatic, familiar and attractive vertebrates, and that adopting these biases in law could threaten biodiversity conservation.
Specific concerns are directed at the draft prepared by the Ministry of Social Rights and the 2030 Agenda for restructuring human–animal interactions. The scientists contend that the bill focuses on a few domesticated species and may conflict with European and Spanish laws and core management strategies for biodiversity.
Attention is paid to stray cat colonies, defined as high-density groups sustained by artificial resources. The bill reportedly aims to provide them with both nutritional and veterinary protection and support, and to grant official status to their volunteer caregivers.
Moreover, the proposed ban on eliminating cats would replace culling, a method that has reduced cat populations on many islands, with fertility control described as more ethical. Yet the researchers warn that fertility control lowers populations only when applied at high rates over extended, connected areas, a scenario that entails very high costs and complex management challenges.
Adverse effects on public health
The authors warn that overly complex and often unaffordable management could sustain or even increase the feral-cat population in cities and rural areas, thereby prolonging and deepening biodiversity damage in the short and long term.
Images show a person feeding stray cats, emphasizing the real-world nature of the issue. The letter argues that the medium-term goal of environmental laws should be to reduce feral cats and cat colonies, paired with efforts to raise public awareness about their harmful effects on biodiversity and public health through clear communication.
It is noted that the ministry’s proposals for the 2030 Agenda can appear contradictory, as some aims to halt biodiversity loss may conflict with measures that could worsen biodiversity pressures. Wildlife management is acknowledged as sometimes raising ethical questions, but the well-being of individual animals is weighed against broader ecological goals. Critics fear policy choices may prioritize a small number of favored species over overall ecosystem health.
Given these concerns, the scientists advocate reducing the negative effects of free-roaming cats by lowering their numbers as quickly as possible and limiting outdoor access for owned cats where feasible. A glance at Barcelona, which reportedly has more than 9,000 stray cats, illustrates the scale of the problem. The letter is signed by researchers from several institutions, including Pablo de Olavide University, Doñana Biological Station, Miguel Hernández University, the Mediterranean Institute for Advanced Studies, and CSIC-affiliated institutes.
Illustrative material includes a schematic representation of known effects of feral cat colonies on biodiversity and humans. The letter to the scientific community and the public is available in a published article, and the draft law can be studied through official channels. Marked citations provide attribution to the original sources for readers who want to explore further.
In closing, the writers emphasize the need for practical, evidence-based policy choices that balance animal welfare with biodiversity protection, public health, and ethical considerations. The debate continues as researchers, policymakers and the public weigh the best path forward for coexistence and conservation.
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