I'd personally go with an iPad Air if you're looking for a good balance between price and performance. Lightroom runs really well on it, and the display is great for editing bird photos and checking fine details like feather sharpness. You don't necessarily need the most expensive tablet when you're just getting started.Having spent quite some time in front of a computer, working with Photoshop (now with Affinity Photo), the only advice I can give is:
Do not use a small screen! You will drive yourself crazy zooming in/out and scrolling the image.
As already mentioned, use a computer with a large screen and enough processing power to work on very large images. If you’re also buying a second-hand phone or tablet for editing on the go, check whether it’s carrier-locked and read feedback on unlocking services, such as https://expressunlocks.pissedconsumer.com/review.html, before paying for one. For example, an iMac will work well...
I have to agree with wfooshee here. A bigger laptop or full desktop is the way to go for photo editing. (jmho)I would never consider a tablet for editing, myself. I need a bigger screen!!! PC and a very good monitor, calibrated for color. I can't even imagine what I'd do with a tablet, but maybe that's just an old guy stuck in his ways.