Because I care about the equivalent focal length, I am entangled between Canon 5D4 and 90D, so I prefer to shoot birds. Which one should I buy? How to choose?

Care about the equivalent focal length. Do you like this or hate this? If you like the same focal length, the half-frame machine does have some advantages over the full-frame machine at the same focal length, but you can't forget that the machine in Quan Huafu will have better image quality than the half-frame machine.

If you hate the equivalent focal length, half a frame is equivalent to no wide angle, but the main body mainly wants to shoot birds, which can be almost ignored.

Canon 5D4 is a product of 20 16, and its continuous shooting speed is about 7 frames per second.

Canon 90D was launched at 20 19, and its continuous shooting speed is about 10 frame/second, which means that 90D has more advantages in bird shooting.

I personally think that 90D has more advantages if the budget is set aside. Brand-new processor, the effective pixel is a little higher than 5D4, which is relatively suitable.