Why don’t males add as many chucks as they possibly can? Because their audience doesn’t consist of just females. Hungry frog-eating bats and blood-sucking midges are listening, too, and they are also more attracted to males with more complex calls. For these frogs, courtship is a risky business, and the balance between lust and danger—between sexual and natural selection—determines how complex they’re willing to make their calls.

Cities change that calculus, because bats and midges both stay away from night-lit homes and streets. These sources of light pollution create a halo of safety, in which túngara frogs can be the best singers they can be, without risking their own lives. “There’s no limit anymore, so the urban males can go wild,” says Halfwerk. Indeed, his team found that in towns, males call more frequently than in forests, and with more chucks. These more complex tunes are more irresistible to females from any location. All else being equal, urban males just sound sexier.

It’s clear that the sights and sounds of cities are problematic for many animals. Bright lights can disrupt the flights of moths and migrating birds, and send turtle hatchlings scurrying away from the sea. Loud noises can drown out mating calls, mask the approach of predators, and drive animals away. One team of scientists demonstrated this in dramatic fashion by playing the sound of traffic through speakers lashed to trees. This “phantom road” drove away a third of the local birds, and suppressed the weight of those that stayed.

But animals can also adapt to urbanity in positive ways. As my colleague Paul Bisceglio reported, there’s increasing evidence that city life can make the animals within them smarter, or at the very least more flexible. When Halfwerk moved urban túngara frogs to forests, the males could dial back the complexity of their calls to avoid bats and bugs. But the reverse wasn’t true: Forest males don’t suddenly croon with more complexity when entering the big city.

Read: Are cities making animals smarter?

Many studies have shown that “wildlife in urban areas are responding to human modifications,” says Danielle Lee, an urban ecologist from Southern Illinois University Edwardsville. “Birds are singing through the night because of light pollution, and raccoons and squirrels are becoming cleverer in overcoming barriers to access food.” But it’s unclear whether reptiles and amphibians would react in the same way, given that they’re more sensitive to environmental conditions than mammals and birds. To see at least one study in which some frogs are adapting to city life “is good news,” Lee says.

In fact, there are now two such studies. A few years ago, Jennifer Tennessen from Pennsylvania State University found, through laboratory experiments, that wood frogs—a common North American species—are disturbed by traffic noise, which chronically raises levels of stress hormones in their bodies. But in the wild, “we were still seeing them in roadside ponds, and they were thriving,” says Tennessen. “It seemed like this mismatch.”