• Since the 1980s, a former copper mine in Montana has been flooded with toxic groundwater.
• The lake is so toxic that birds that land on it get burned from the inside.
• A group of experts uses guns, fireworks and other high-tech tools to rescue birds from the surface.

Migrating birds that land in Montana's Berkeley Pit are likely to die within a matter of hours. To scare them off, miners now use drones, lasers and rifles.