Bat swarm registered as rain on Phoenix weather radar; bigger swarms expected later this summer

They’re here, and there are so many of them, in fact, that it was picked up on weather radar.

On June 29, thousands of bats emerged from the bat cave along the Arizona Canal Trail, and that's when officials with the National Weather Service encountered a surprise, as the emerging bats registered on radar imagery.

Every year, 10,000 to 20,000 bats fly to Phoenix on their migration path to Mexico. For some reason, thousands of those bats have chosen a tunnel off 40th Street in the Biltmore area to sleep during the day.

Experts say the bats are mostly female, and that those bats are drawn to any dark spaces without humans. In this case, the bat cave in the Biltmore area has become a temporary maternity roost for the bats, where the females incubate their babies until they are ready to fly to Mexico.

"That number, towards the end of the summer, is actually going to be slightly larger. Maybe significantly larger," said Jonathan Derbridge with University of Arizona's School of Natural Resources and the Environment.

The bats have attracted the attention of some people, as they bring their family to sit outside the tunnel until nightfall to watch the summer swarms.

"Coming in at the right time, waiting and being patient, you get to see them coming out, that would be worth it," said one person.

It should be noted that bats rarely attack humans. In fact, they avoid humans. Bats also eat bugs, specifically mosquitoes.

Editor's note: A reminder to viewers from Maricopa County Flood Control:

The channel serves an important public safety function and public access is not permitted. The channel can quickly fill up with storm runoff (often without warning), especially now during Monsoon season. The time of day the bats are flying out also happens to be the time water is most likely to be collecting and flowing in the channel – this runoff can come from quite a distance, so you may not even know that it is heading your way.