Birding made easy: App helps ID San Francisco's flocks

San Francisco hosts a variety of birds, and a new app helps people spot them.

What's happening: Birda, a free app and social media platform, launched in September to encourage people to bird-watch.

• The app helps users identify species, and offers challenges and leaderboards to have fun with other bird-watchers.

Why it matters: Bird populations in the U.S. have dropped by 3 billion since 1970, and more than half of all U.S. bird species are in decline, Axios' Deirdra Funcheon reports.

• Logging sightings of birds can help scientists identify changes in their migration patterns and population levels.

If you start: There are a number of places throughout San Francisco to go bird-watching.

• Around Twin Peaks, for example, Birda lists 212 species to find, including the common raven, California scrub-jay and the ultra-rare red-throated loon.
• On Telegraph Hill, you can find Anna's hummingbird, the white-crowned sparrow and more than 200 other species.