The death of Harambe, a 17-year-old silverback Western lowland gorilla shot dead by Cincinnati Zoo staff after a four-year-old boy fell into his enclosure, has sparked anger and controversy.

One lesson we can take from this sad episode is the need to be realistic about the conditions in which gorillas and other captive animals live. If we accept that gorillas are going to be kept in zoos, we need to make sure those zoos don’t fail these animals by letting situations like this arise.

Gorillas are obviously potentially dangerous to humans. We are a danger to them too, not least because our genetic closeness makes gorillas vulnerable to many human diseases.

As unpalatable as it seems to zoo visitors who might want to see animals living as “naturally” as possible, gorillas need to be kept behind glass, steel mesh or wide divides – for their own safety as well as ours.

Safety-first zoo design

One of the biggest questions about the Cincinnati Zoo incident is how the young boy could so easily have fallen into Harambe’s enclosure and come into direct contact with him. In light of this, there are certain principles that can be followed for the safe design of enclosures for large animals.

If an outdoor enclosure has some type of moat for containment, it may be a deep concrete moat with shallow water (less than 50cm) for gorillas to use without risk of drowning (gorillas can’t swim).

According to one set of recommendations, the typical minimum barrier should be 3.65 m high and 3.65 m across, but there is no law concerning minimum standards for gorilla enclosures. For extra security, a second barrier, sometimes electrified, is needed to keep people away.

In terms of minimum standards, the Cincinnati Zoo enclosure is suitable. But for great apes such as gorillas, it should no longer be acceptable simply to meet minimum standards. This is as true for containment as it is for the animals’ other needs: space, complexity, and behavioural and psychological stimulation. The cost of building optimal enclosures for gorillas runs into millions of dollars, which places constraints on zoos who rarely have the funds to upgrade or redevelop enclosures. Who should fund these improvements?

All zoos have regulations and procedures to follow for risk management, including animal escape and recapture. Additional precautions are taken for all incidents or interactions with those considered dangerous species (such as big cats, great apes, elephants and so on).

There are strict legal requirements for protecting the public. But because of the rarity of such events, zoo staff may be inexperienced with situations involving human intruders (accidental or otherwise) in an exhibit.

Are gorillas ‘gentle giants’?

In 1996, a three-year-old boy fell into a similar enclosure at Brookfield Zoo. While the zoo visitors were also screaming and yelling, an eight-year-old female gorilla, Binti Jua, “rescued” the boy by carrying him to zoo staff at a side entrance. As animal researcher Marc Bekoff points out, Binti Jua was hailed as a gentle “heroine”, whereas Harambe was treated as a threat, but in both cases the gorillas were in situations where they had no control over the outcome.

It is impossible to say for certain whether Harambe would have become aggressive. He appeared to show behavioural signs of stress – hardly surprising given that people were shouting and screaming at him. Gorillas are sensitive and respond to non-verbal behaviour, such as towering over them or staring at them, which can be seen as a threat.

When faced with a stressful, noisy and threatening situation, gorillas – like most other animals, humans included – have a physiological “fight or flight” response. It is hard to predict how any individual will react under stress, but based on the video footage, Harambe did not appear to be behaving aggressively.

Silverbacks are powerful animals, weighing up to 180kg. When they are living in stable groups and not facing a threat, they are indeed gentle, but adult silverbacks can engage in infanticide when taking over a new family group.

A 2005 study found that the behaviour and welfare of gorillas in zoos are influenced by the number of people nearby, how close they are, and how much noise they are making. While zoo visitors can behave in almost any way they want, in the wild there are strict guidelines for tourists visiting gorillas.

To avoid disease transmission, behavioural disturbance and stress for wild gorillas, tourists who visit their native habitats must be over the age of 16, and in groups of no more than eight. The guidelines allow them to spend one hour quietly watching from a distance of about 10m.

Gorillas may be “gentle giants” when treated with respect and awe, but they are so much stronger than us.

Expectations vs reality

When gorillas are housed in zoos, their exhibits must be designed from three perspectives: the safety and wellbeing of gorillas in the enclosure; the safety and satisfaction of visitors; and the safety and ease of maintenance by keepers and other staff.

These aims aren’t always mutually compatible. Zoo visitors might expect gorillas to be visible, active and “entertaining”, whereas the gorillas themselves are likely to seek quiet, secluded areas, and to spend much of their day resting or foraging.

Zoos and wild gorilla tourism sites must manage their visitors’ expectations, so that all visitors understand that animal welfare and comfort take priority over optimal viewing.

We also can’t pretend that gorillas have control over their lives in captivity or even in natural habitats. They are impacted by human activities in all the places they live. Conservation is far more complicated than merely ensuring that gorillas have somewhere to live.

Zoo-based management programs have to deal with issues such as providing long-term care for old gorillas, who can reach 50 years of age. Captive breeding programs also have to deal with a “surplus” of males, because only a subset of silverbacks form family units or harems, which feature multiple females. In the wild there are many different group formations, including those with multiple silverbacks, but in captivity it is harder to manage social groups, as there is rarely space to separate individuals when aggression occurs.

Meanwhile, sanctuaries in Africa are struggling to care for orphaned gorillas as a result of the bushmeat trade. There is no truly safe wild haven for gorillas. Populations of critically endangered Western Lowland gorillas are declining, mainly as a result of the Ebola virus, which has killed thousands of gorillas in the Congo Basin, as well as commercial hunting and human disease.

Do gorillas belong in zoos? Why do zoo visitors want to see large animals in urban zoos? Are gorillas safer in the wild than inside enclosures and, if so, where? These are questions on which there will inevitably be strong differences of opinion.

But one thing we should all agree on is that we must strive to be compassionate and foster peaceful co-existence between people and other species, and work towards creating safe environments for gorillas with minimal human impact.

We can’t pretend that a moated enclosure without bars is any less of a cage than one with mesh. If keeping them safe in a zoo means putting a bigger barrier between us and them, or only letting us view them via hidden cameras as they live in a more protected and secluded exhibit, then so be it.