How a Phoenix storm drain provides a home for thousands of bats

The humming sound of the cicadas gives way to a high-pitched screech. The sky darkens. Some people sit on folding chairs and turn their heads to the sky as small black blobs emerge from a drain, at first one by one, then in droves.

On one side of the drain is written “No Trespassing” and on the other side is a sign with information about Mexican free-tailed bats. Bats are visitors to Phoenix during the summer, the season bats are born.

The storm tunnel, dubbed the “Phoenix Bat Cave” on Google Maps, runs along the Arizona Canal near North 37th Place. The 16.5-mile-long, partially underground concrete tunnel collects and diverts water away from people and property during storms, especially during the monsoon. It is also home to thousands of bats. The initial estimate of 10,000 seasonal residents may double by August as each female in the mother colony gives birth.

The tunnel opens again 3 miles away, releasing more bats into the city each night.

“I come out here with my wife and brother-in-law a few times a year to see the bats come out,” said Bill Hutchison, a spectator who said he has been to the bat cave many times. “Nature is cool.”

Arizona has 28 species of bats, more than almost any other state in the US. They often choose to shelter in buildings, bridges and other man-made structures such as bridges and storm tunnels.

The Mexican free-tailed bat is the most common species in the Southwest. They are medium in size and you can hold one between a few fingers. Their fur is usually reddish or dark brown, and their wings are long and narrow. They also have the highest horizontal speed of any animal.

Mexican freetails “feed on the wing,” meaning they pluck insects from the air in flight, said Angie McIntire, a bat specialist with the Arizona Game and Fish Department. McIntire said freetails eat moths, flying ants and other insects from the air.

The species migrates from Mexico, and free-tailed females form maternity colonies where they give birth to a single child. Freetails make the phoenix bat cave their summer home, from which they emerge dramatically each night to feed.

The cave, officially known as the Arizona Canal Diversion Channel, was established by the Maricopa County Flood Control District in 1994.

A tall metal fence runs the perimeter of the long concrete slope leading into the tunnel, where spectators usually line up. The smell of bat droppings, or guano, rises from the cave when the breeze is low.

Female Mexican free-tailed deer began resting in the cave shortly after it was completed, said Lisa Blyler, public information manager for the Flood Control District. They have been there every summer since.

Hally Cokenias, president of Arizona Bat Rescue, the state’s only exclusive bat rescue, said she receives rescues from the Arizona Canal “all the time.” She releases free tails of rehabilitated mother and child who end up in her care.

Cokenias and her business partner, Benjamin Largent, keep about 15-20 bats in a warm, dark room in her Mesa home.

“We’ve been really into bats for a long time and we were looking for a place to volunteer and there wasn’t one,” Cokenias said. “So we decided to figure it out and start our own rescue.”

Flying mammals have delicate, translucent wings with flexible bones. They are brought to her with broken toes, dehydration and damaged membranes, usually on the paws of outdoor cats. Many of the bats Cokenias rescued from the canal got stuck in the water while trying to get a drink in flight, she said.

Very few of the bats they rescue have been injured as a result of conflict with humans or human infrastructure.

People can get the wrong idea about bats, Cokenias said, and there’s a fine line between wanting people to be safe but not wanting them to be afraid of bats.

There are also a lot of misconceptions about bats and rabies. Not all bats have rabies, she said, and you have to be bitten by a rabid bat to get it. Most sick bats end up on the ground, so the ones flying past your head probably won’t hurt you.

Bats also provide pest control. They eat agricultural pests and other insects.

“Another thing they do wrong is they think they’re ugly,” she said. “They’re actually incredibly cute.”

The “pungent” smell welcomes visitors to the cave

Erick Arntz, the Flood Control District’s director of operations and maintenance, stops the truck about 1,000 feet into the cave. The voices of flood control personnel echo indistinctly at the opening, a distant square of bright sunlight. In the opposite direction, the tunnel stretches into complete darkness. Other parts of the tunnel have been used as sets for zombie apocalypse movies, Arntz says.

As she prepared to lead reporters deep into the cave, Blyler called the cave’s smell “pungent” and said she had to wash the stench out of her nose with soapy water after her last visit.

Guano spreads the concrete. A few bats swoop down, disturbed by the truck. Flood control deliberately does not go this far into the cave during the summer to avoid disturbing the bat colony. During the rest of the year, the department conducts weekly visits by car to check the tunnel for damage, sediment build-up and debris such as rocks, trees and trash.

The tunnel ceiling is lined with thin horizontal cracks in the concrete. These gaps are perfect for bats to hang out in, a “happy accident,” says Arntz.

Technically, the area around the cave is private property, but the Flood Control District encourages people to go watch the bats take flight.

“It’s a really cool experience,” Eliana House said at ACDC’s western opening. House said her son’s kindergarten teacher taught her class about bats and brought them to the cave. She watched as the stream of bats slowed, like the way popcorn finishes popping: bats still popped, but only a few at a time.

“I’m Night Fairies”

There are at least a few visitors most summer nights. Spectators park in a nearby neighborhood, runners and walkers emerge from the canal path, and parents bring their children and hoist them on their shoulders for a better view. They set up chairs, take videos and talk in low voices as the bats start to emerge, laughing when one of the bats approaches their head.

On the eve of the Fourth of July, the Phoenix Bat Cave was busy. People lined the fence to watch. Within 24 hours, the sky would be decorated with fireworks, but on July 3rd it was spotted with bats. They lay on the deep blue and danced across the canal in the red-gold light of the setting sun.

“It’s magic,” Cokenias said. “They are night fairies.”

A little over a month later, on August 6, the crowd was small. Only a few people hung onto the fence to watch. Bat flow was easier.

Among the spectators was John Gunn, a former wildlife manager for the Arizona Game and Fish Department. He said the bat cave is unique because it is an entirely man-made structure that bats have adapted to. It’s rare for anything in his concrete-and-steel business to benefit wildlife, he said.

“To see hundreds and hundreds of these bats benefiting from this structure … it’s beautiful. As a biologist, as a human being, let’s see how we help our little wild friends while also taking care of our own needs.”

Weidheiden

How a Phoenix storm drain provides a home for thousands of bats

The “pungent” smell welcomes visitors to the cave

“I’m Night Fairies”

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