Birding Camera Optics Question

[pstra...@gmail.com]

Need assistance understanding pixel pitch effect on resolution.
Due to life changes, I am now birding using my camera at the limits of its abilities.

My Nikon D7200 plus 300mm zoom lens is aging, and I want to replace it with a Z 6 iii mirrorless with 200mm zoom plus 2x telextender. The D7200 has 3.89 µm pixel pitch, the Z 6 iii has 5.92 µm. Am I correct that, all things being equal, this means worse resolution at the same distance?
I had been thinking that better image stabilization, larger sensor, and newer electronics would be an advantage, then it occurred to me to check the pixel pitch. I really don't want to spend thousands of dollars to make my remaining birding years worse. Any advice greatly appreciated.
The picture attached (I'm thinking red tailed hawk) is taken at the limit of my D7200 rig.)  I hope this image clarifies my dilemma. Image taken in North Boulder CO on 2 24 2026.

[Caoimhín Perkins]

A larger pixel size means lower resolution, yes. If you image a photo made up of squares (which is what a digital image is), a photo with smaller squares will have smoother curves on it as opposed to noticeably blocky shapes from point to point. This becomes more of an issue when you really zoom in; it will not be as big an issue for things nearby. The trade-off is that smaller pixels have a smaller “bucket” to collect photons, so in low light conditions, like twilight or night, smaller pixels need more time to create a brighter image than sensors with bigger pixels. Just something to think about if you plan on looking for nightjars and owls.

[Caoimhín Perkins]

Also just want to add that smaller and smaller pixels does not necessarily mean better. 3.89microns is good but going below 2microns (I believe?) presents issues with diffraction which will create more pixel noise.