Bird migration through Oregon plummeted this spring

By the numbers: Using BirdCast, a tool that measures migration with radar and weather data, experts estimated some 42.6 million birds passed over Oregon this year through the beginning of May.

• That's a 47% decline from last year during the same period.
• Numbers picked up more recently, but the state is still behind last year's numbers by 35% through mid-June and 28% off the five-year average.

Zoom in: The cause of the decline isn't clear, though there have been droughts in some migrating birds' wintering grounds along with water shortages and wildfires throughout the West.

What they're saying: "All of this data crunching gives us more numbers than answers," Brodie Cass Talbott, adult engagement manager with Bird Alliance, wrote in a blog post.

• "But, with threats to birds increasing, and our abilities to monitor them increasing, we should expect more efforts ahead to identify population-wide trends in real time, in the hopes that we can more quickly address serious conservation issues," Cass Talbott wrote.