A fleet of drones patrolling New York City’s beaches for signs of sharks and struggling swimmers is drawing backlash from an aggressive group of seaside residents: local shorebirds.

Since the drones began flying in May, flocks of birds have repeatedly swarmed the devices, forcing the police department and other city agencies to adjust their flight plans. While the attacks have slowed, they have not stopped completely, fueling concern from wildlife experts about the impact on threatened species nesting along the coast.

Veronica Welsh, a wildlife coordinator at the Parks Department, said the birds were “very annoyed by the drones” from the moment they arrived on the beach.