I've gotten interested in this subject too. But the thing is; it's not worth €100+ to me. A Dahua camera would be the easiest (easy integration with other camera's and NVR) but the cheapest one (
IPC-T2431T-AS) is still close to €100.
Dahua doesn't seem to stock cheaper camera's anymore. Also the
IPC-K42A could have been interesting; but also EOL.
All other options have their drawbacks.
ESP32-cam is dirt cheap, but very poor performance. (also no IR, no audio, no ethernet etc.).
I have some Yi camera's (with custom firmware) Image quality is fine but stability is very poor. Also no ethernet.
So camera's are either not good enough or they're to expensive. (for this purpose; it would just be a little fun thing on the side).
As for the bird recognition; there's lot's going on with AI. You could make custom models if you want: