Residents of Richmond, a Bay Area town north-east of San Francisco, are grappling with a disturbing mystery after multiple birds were found dead, with some appearing to “explode” mid-air.

Security footage from one neighborhood captured a bird falling from a power line after a loud popping sound. Concerns and speculation followed.

Residentssaid they have found as many as 50 dead birds in the area over the past several months. The story was first reported by ABC7.

Officials for the California department of fish and wildlife told the Guardian on Wednesday that the department’s wildlife health lab received two dead birds for evaluation that had been collected by the utility company Pacific Gas & Electric. One of the birds was a mourning dove and the other a European starling.

The lab found no signs of electrocution in the collected birds, but the creatures did show injuries that could have been caused by a pellet gun, a BB gun or a slingshot.

“The exact cause of the trauma to all of these birds could not be determined,” the department confirmed on Wednesday, adding that wildlife officers were investigating the mysterious deaths.

The investigation came as some neighbors blamed PG&E for faulty cable lines, and urged the utility company to look into the incident.

“We appreciate the concern of our customers in Richmond about the recent series of bird deaths,” Tamar Sarkissian, a PG&E spokesperson, told the Guardian. “PG&E does not believe that there was an issue with our electrical equipment and agrees that these birds were not electrocuted.”

According to Sarkissian, neighbors have also asked the Contra county sheriff’s office to look into this situation.

Resident Maximillian Bolling told ABC7 that he watched birds land on power lines only to burst apart moments later.

“So when they land and it happens, they just quickly explode and it’s really violent,” Bolling told the local station. “It’s very traumatic, super traumatic to see this.”

Richmond residents have made signs warning people and urging others to report the incident if they spot a dead bird, according to the San Francisco Chronicle.

Concerns over the bird deaths come amid broader worries about avian health making headlines across the US. Earlier this year, an outbreak of bird flu spread at high rates through egg-laying chickens, causing egg prices to soar. The virus spreads through contact with infected animals or unpasteurized animal products.

Those most at risk include people who work with poultry or dairy cattle, and people exposed to wild birds or animals, and anyone consuming raw milk or undercooked meat.