According to Zhang, there are only six species of frog in Shanghai now, down from more than a dozen two decades ago. As such, this project aims to depict how these creatures move so that urban planners can cater for them by providing enough space when designing new parks in the city.

That Friday night, the team ended their hunt at 10 pm after locating nine frogs. One frog was missing, and is thought to have been killed by birds. One was found dead, its carcass suggesting that it was probably the victim of a mower.

"I signed up for this citizen scientist project because I really love nature," says Chu, who came from Luzhou, Sichuan province, in 2002 to study in Shanghai.

"There was more biodiversity back when I first arrived," he says.

"But with rapid urbanization, more buildings and developments have taken over nature."