On that theme, greenfinches in the UK are declining rapidly due to disease. Well-meaning people are putting out bird feeders for garden birds, but not cleaning them regularly, or leaving stale food in them, which, in turn, is causing greenfinches to get disease, and killing them off.
The worst of it is, than rhino horn which is deemed so precious to poachers, is entirely made of keratin. This is exactly the same substance as your fingernails, so all these animals have died because of the stupidity of people who thought it was an aphrodisiac.
It's not quite extinct yet. There are still two females alive and plans to use Sudan's sperm in IVF.
The Southern white rhino is so closely related, the females can be used as surrogate mothers for the implanted eggs, to start off a brand new herd.