20 years to eradicate 500,000 birds, that should be an all time high. Humans and their effect on their environment.
They are beautiful birds, thanks to these peeps "Robert Cushman Murphy and Louis S. Mowbray" and the conservation programme they're still in existence.
Nice post 
RE: The Bermuda petrel (Pterodroma cahow) was believed to have gone extinct in the 1620s, but was rediscovered 330 years later