The Stephen island wren in NZ. Apparently it was the only species thought to have been wiped out by a single creature - a lighthouse keeper's cat in 1894. Solution - shoot the cat.
I agree. There colonial breeding habits did'nt help either.Not sure if passenger pigeons would be able to survive in huge numbers much later than OTL. If things happen the way they did OTL and chestnut blight gets introduced to the US around 1900, a major source of food for the pigeons gets wiped out. The American chestnut population went from around 4 billion to a few hundred at most in 40 years.
It seems that what was actually sighted was the closely related Pileated Woodpecker rather than an Ivory-billed. I also feel that they no longer exist.Debate rages on the topic. Personally, I think they are extinct.