> Why we keep killing the birds that survive the infection is beyond me

We don’t know the reservoir capabilities of novel viruses, nor can we confidently rule when a previously-sick bird is well and non-infectious at scale.

> It's an evolutionary pressure that we refuse to allow to work

We’re selecting against birds that get infected in the first place. (Probably to no tangible effect. But the goal isn’t to have birds that can survive a plague, it’s to prevent it in the first place.)