Any bird photographer will tell you - there is no end to the misery of seeking better bird pictures. Not close enough? Buy lenses of longer focal length. But affordable lenses are often 'dark' f5.6 - f6.3, which means that high shutter speeds need high ISO (sensor sensitivity) values.
So, you also need a camera with exceptional performance at high ISO. But these are often good at high ISO because they have a relatively low pixel count. Ahh, so that means that cropping is going to be less acceptable.
Maybe but a faster lens? Two issues: price (some of them are in 'eek!' territory) and weight, often high enough to obviate hand holding.
My perfect camera/lens for birding? A 40-ish megapixel camera with no noise at 12,800 ISO and capable of 10 frames per second. This would be coupled to a super sharp 600mm f4 lens that weighs no more than 2kg, focuses in milliseconds. Ahh what the hell, since it is fantasy system anyway (that probably contradicts rules of physics) make it a 600mm f2.8.
Oh yes, the entire system must cost no more than two grand.
Back to reality...