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Every city has a distinctive sound—a blend of street traffic and distant sirens, rustling leaves and urban wildlife. But for years, the soundscapes at intersections across America shared something remarkable. Whenever certain pedestrian signals changed to "walk," one of two bird-like electronic noises played. One alternates between two tones, like a cuckoo clock. The other chirps approximately once per second.

The setup, which plays one (the cuckoo) for north-south crossings and another (the chirp) for east-west, is called a cuckoo-chirp signal, and there’s a hint in the name: Both sounds are based on recordings of cuckoos from Japan, where the technology was first developed. The sounds provide the same information as visible signals—when it might be safe to cross the street—for pedestrians who are blind or visually impaired.

But the age of the bird-call pedestrian crossing is drawing to a close. After decades of widespread use, they’re being phased out after the federal government, in 2009, recommended a switch to other sounds—in no small part because pedestrians sometimes confused crosswalk chirps with actual avian singing.

“When that was all there was, we were grateful to have it,” says Becky Davidson, chair of the of the American Council of the Blind. Davidson is a blind person who  and their handlers as outreach manager at Guiding Eyes for the Blind, a New York non-profit. “But cuckoo-chirps should be going away as soon as traffic signals are updated,” she says. “They should not be put in as new signals.”

Though visible pedestrian signals were first installed in the United States in , audible signals only began to spread in when disability advocates fought for a range of accessible infrastructure such as . In many cases, the cuckoo-chirp signal was the first audible cue available to blind or visually impaired people .

At the time, U.S. companies either imported equipment from in Japan that used existing cuckoo-chirp recordings or copied the sounds for their own designs. The original recorded calls are believed to belong to the Common Cuckoo, a migratory species common across most of Europe and Asia that regularly strays to Alaska. (Nagoya Electric Works did not respond to a request to confirm this information.) The design spread across the United States, and soon became a de facto accessibility standard and recognizable part of the urban soundscape.

Years after the cuckoo-chirp’s American debut, Congress passed in 1990 the Americans with Disabilities Act. The new law, combined with general interest in pedestrian safety, led researchers to study whether bird-chirp signals were effective. More than a decade of research led to a comprehensive for the National Cooperative Highway Research Program. It recommended discontinuing use of the cuckoo-chirp.

“This was one of the most satisfying projects that I ever worked on,” says traffic researcher David Harkey, a co-author of the 2007 report and now president of the , an organization known for its safety ratings from vehicle-crash tests. “It resulted in an immediate change in policy that had a real-world effect.”

The report highlighted a few problems with the sounds. The signals can be hard to hear, for starters. “The cuckoo [call] is fairly distinct. The chirp can be difficult,” Davidson says. “Those signals can be easily drowned out by traffic noise or wind.” Additionally, the two-sound system was burdensome. In practice, visually impaired pedestrians struggled to orient themselves to compass directions; sometimes the sounds were accidentally installed in reverse.

Confusion with wild bird calls is another potentially dangerous concern. In polls, around 10 percent of blind or visually impaired pedestrians had mistaken a cuckoo-chirp signal for a bird, causing them to wait at a curb unnecessarily. Worse, about the same proportion had mistaken a real bird for a walk signal, potentially compelling them to cross against traffic. Some people even reported birds mimicking the cuckoo-chirp signal—most likely impressionists like the European Starling, Northern Mockingbird, or Gray Catbird. of Elon University, who studies mockingbird mimicry, says that a bird mimic doesn’t need to spend much time near an audible signal to learn the call. “They have an acoustic template,” he says. “When sounds fit in that template, they’re much more likely to imitate.” In the case of Northern Mockingbirds, he says, chirps seem unlikely, but crosswalk cuckoos fit the bill.

The recommendation against the cuckoo chirp went into the 2009 , a federal best-practices document for all traffic conventions, from road markings to signage to signals. Since then, cuckoo-chirp sounds across the country have been replaced with others optimized for the vision-impaired. Traffic-device companies now offer a , spoken messages that adjust their volume according to ambient noise, and a quiet tone that locates push buttons which vibrate when the light is green. Indeed, two manufacturers told �ԹϺ��� that they no longer sell equipment with bird-like noises at all, specifically citing the guidelines.

Though some pedestrians may miss the chirping cuckoos at the crosswalk, these signals are first and foremost an effort to make cities equitable places to live. “People who are blind or visually impaired need to have equal access to their environment,” Davidson says. “That’s why accessible pedestrian signals are so important.”