The noises of nature sometimes carry broader meanings. The howl of a wolf signifies that wildness endures. The gronk of Canada geese moving south overhead reminds Americans to brace for winter. The sound of a coughing gorilla signals that Covid-19 is an even bigger problem than we thought.

Scientists use another fancy term for when the spilling goes back, or onward, from a human to some nonhuman animal: anthroponosis.

Early last month, two gorillas started coughing at the San Diego Zoo Safari Park, a compound of open-air enclosures for wild animals, an annex to the city zoo but separate, out in an arid valley just east of Escondido. These gorillas were among a group of eight residing amiably there, on a patch of artfully constructed habitat known as the Gorilla Forest. Testing of fecal samples showed that SARS-CoV-2, the virus that causes Covid-19, was among them. It could only have come from a person.

As for wild animals in captivity, the Association of Zoos and Aquariums, together with the American Association of Zoo Veterinarians, has issued an alert to members, with bulleted points of advice, one of which is that people should practice social distancing from big cats such as tigers. (Most of us knew that without being told.) Another is that staff should immediately report anything unusual. Coughing, for instance.