Zoo

University of Zurich: Zoos Should Deliberately Cull Surplus Animals

What happens to surplus animals in zoos? Until now, reproductive control has usually been the preferred approach. Researchers are now advocating a rethink: through professionally conducted culling, zoos can maintain their reproductively viable populations, raise awareness of the challenges of species conservation — and improve animal welfare as well as their carbon footprint.

Editorial team Wild beim Wild — 8 January 2025

Unlike animals in the wild, zoo animals are under considerably less pressure.

They have sufficient food available and are not hunted by predators. As a result, animals in zoos typically live far longer than they would in the wild. This in turn presents zoos with the challenge of optimally managing their limited capacity.

For logistical and financial reasons, many zoos restrict the breeding of their animals. Other zoos take a different approach and cull surplus animals — risking public backlash in the process: the killing of Marius, a healthy two-year-old giraffe, sparked an international debate ten years ago about what zoos should do with their surplus animals.

Zoo populations are ageing

In an opinion piece led by the University of Zurich, researchers now argue that widespread contraceptive practices are altering the age profile of zoo populations — and not for the better. “Reproduction is a fundamental need of animals. Without reproduction, they are deprived of one of their most important evolutionary drives,” says Marcus Clauss of the UZH's Vetsuisse Faculty and lead author of the study. “Over time, zoo populations grow increasingly old, which jeopardises one of the core principles of zoos: the preservation of their own populations.”

Surplus animals often cannot be housed elsewhere, as space in zoos is limited and reintroducing animals into the wild requires specialized programs and suitable habitats. Researchers therefore advocate for planned and professionally conducted culling of surplus zoo animals. “We consider this to be rational and responsible population management. Furthermore, this approach can help zoos fulfill their educational mandate,” says Clauss. The Leipzig Zoo recently culled four sitatungas due to lack of space.

The natural life cycle of animals as an educational mandate

Every year, more than 700 million people visit zoological institutions around the world. “Zoos can help promote public understanding of the natural life cycle of animals. However, by pushing the death of animals to the margins, zoos perpetuate unrealistic expectations about life in the wild,” explains co-author Andrew Abraham of the University of Aarhus.

Zoos also have a duty to maintain animal populations. In doing so, they make an important contribution to species conservation. “Many animal species are already threatened with extinction today, and in the coming decades many more will join them. It is therefore crucial that zoos maintain breeding populations and the knowledge of how to raise young animals. What we do not need is a collection of geriatric animals – and veterinarians occupied with palliative care,” adds Abraham.

In-house meat supply improves carbon footprint

If there are to be more births in zoos, surplus animals must be permitted to be culled. One zoo in Germany is thereby able to feed its predators with up to 30 percent of the meat from animals within its own facility, reducing its carbon emissions and its reliance on commercially slaughtered livestock.

Even when the killing of mammals such as the giraffe Marius frequently sparks controversy, there are indications that public opinion is more balanced than portrayed in the media. “Zoos have a responsibility to educate their visitors about the realities of life and death in animal husbandry,” says Clauss. “Transparent communication can help change public perception and increase acceptance of long-term, sustainable approaches.” More on the debate around Animal Rights.

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