A new reason to take the phone on the dog walk

The flamboyant cardinal is a loudmouth and the tiny Carolina wren is a boisterous chatterbox.

You'll start to recognize all the resident birds — and occasionally a stranger on the wing — in your neighborhood with the magical Merlin Bird ID, a free app from the Cornell Lab of Ornithology.

Merlin is a breakthrough for both serious bird watchers and for people just strolling through a park. It includes a feature called Sound ID that listens through the phone's microphone and names the birds singing around you as they sing. Even when there is a chaos of birds in the park, the app can identify every separate song. You don't even need a cell signal to discover the birds around you.

The cardinal at the feeder turns out not to have one song. Both the male and the female sing, and researchers have described at least 16 different cardinal calls, according to the Cornell Lab. The teakettle-teakettle rolling out of a tangle of vines belongs to a Carolina wren, a bird that weighs less than an ounce and puts out a startling number of decibels for its size. Cornell reports that one captive male sang nearly 3,000 times in a single day.

The app is not listening the way a person listens. It converts the sound into a spectrogram — a picture of pitch and volume over time — and then identifies that picture the same way it identifies a photograph of a bird. Automatic song identification went nowhere for decades until researchers stopped trying to analyze sound and started treating it as an image. Nonetheless, the app records and stores your favorite bird moments and gives you a photo and description of your birds.

Sound ID covers 2,066 species. That number goes up twice a year, on recordings made by people holding up their phones on their own walks.