The debate over cats, biodiversity, and new animal welfare proposals
A group of Spanish scientists recently published a critical letter arguing that domestic cats are a major threat to global biodiversity. They contend that a government bill for animal protection, rights, and welfare—approved three months ago—clashes with European biodiversity strategies. Their view is stark: in the medium term, environmental laws should aim to reduce or even eliminate environmental threats posed by free-ranging cats, including cat colonies.
The letter, featured in Conservation Science and Practice, consolidates findings from several recent studies on felines and their ecological effects. Notable points include:
- Domestic cats are linked to more than a quarter of recent extinctions among birds, mammals, and reptiles, marking them as a highly problematic invasive predator.
- Cats represent a leading cause of mortality for small mammals and birds, surpassing other threats like poisoning or direct hunting by humans.
- Well-managed cat colonies continue to hunt wildlife, and high densities in feral populations can exceed the impact of individual domestic predators on prey populations.
- The consequences of cat predation are particularly severe on islands, and existing Spanish laws may hinder protecting endemic species in places like the Canary and Balearic Islands.
- Cats act as vectors and reservoirs for numerous diseases, with potential risks to wildlife and public health.
- High-density colonies can drive disease dynamics due to close contact among cats and interactions with owned and feral populations.
Critique of animal welfare legislation
The letter opens by tracing how moral consideration has expanded beyond humans to include nonhuman beings. As a result, many laws around the world now grant some form of rights to animals. The authors urge readers to examine how these moral shifts translate into policy and practice.
They highlight a case study of a draft law and the 2030 Agenda proposed by the Ministry of Social Rights to reorganize human-animal interactions. The scientists argue that the focus on a few native species may conflict with European and Spanish biodiversity management frameworks, potentially undermining established conservation goals.
The draft places particular emphasis on stray cat colonies—dense groups sustained by artificial food sources. The intention appears to be to provide nutritional and veterinary support through local administration and to grant official status to volunteer caregivers.
Additionally, the bill proposes banning culling and instead relying on fertility control to reduce cat populations. The researchers describe fertility-based approaches as more ethical in principle, but they warn that successful population declines require sustained, high-rate application over wide areas, a combination that entails significant costs and complex logistics.
In their view, high costs and unintended consequences must be managed if fertility programs are to work effectively, especially when population dynamics are described as highly persistent in space and time.
Public health implications
The scientists argue that current management strategies are often too complex and expensive, risking the persistence or growth of feral cat populations in urban and rural settings. In the short term this can amplify harmful effects on biodiversity, even if long-term aims exist to reduce impacts.
A reflective note accompanies a scene of volunteers and cat colonies: the image underscores the tension between compassionate care and ecological risk. The authors call for clearer messaging to highlight the negative effects of free-roaming cats on both ecosystems and human well-being.
They further critique proposals that claim to strengthen biodiversity protection while being overseen by the same ministry charged with delivering the 2030 Agenda. The concern is that such alignment may foster policies that, in practice, favor a small set of admired species over a broader conservation remit.
Ethical considerations surface again when wildlife management appears to privilege certain populations over ecosystem health. The authors warn this could produce biotas dominated by a few favored animals, rather than diverse, resilient communities.
To mitigate these risks, the authors advocate for policy instruments aimed at reducing the negative effects of free-roaming cats as quickly as possible and limiting outdoor access for owned cats where feasible. The call is for proactive measures that pair welfare with biodiversity protection.
As an illustration of scale, the letter notes that Barcelona alone hosts more than 9,000 stray cats, illustrating the magnitude of the challenge. The work is signed by researchers from Pablo de Olavide University, Doñana Biological Station – CSIC, Miguel Hernández University, Mediterranean Institute for Advanced Studies – CSIC-UIB, and the Institute of Natural Products and Agro-Biology – CSIC, among others.
A schematic figure accompanying the discussion outlines known impacts of feral cat colonies on biodiversity and human health, serving as a visual summary of the risk landscape.
For reference, the original Spanish study and related documents include the letter by Spanish researchers and a preliminary bill for animal protection: Letter: Spanish researchers. URL references are provided for consultation in the cited materials.
Citations: Letter from Spanish researchers (Conservation Science and Practice); Preliminary bill for animal protection and welfare (Ministry materials). See the cited URLs for the original documents.
Environment department contact address: [address redacted per policy]