Quick reply while I am checking my kit... I have been very satisfied with how the R7 handles different focal lengths, but weight distribution is a major factor for birding. Before giving a definitive answer, are you planning to shoot primarily handheld or will you be using a gimbal/tripod setup? A few technical tips for your consideration:

• Update your R7 firmware immediately to improve eye-tracking stability when using slower lenses.
• If you are worried about the f/9 aperture but want L series quality, the Canon EF 100-400mm f/4.5-5.6L IS II USM paired with a Canon Mount Adapter EF-EOS R is a very reliable choice. I have been using that adapted setup for months and it works well with the high pixel density. It provides a much faster aperture than the 200-800mm and stays well within your $2500 budget.

Honestly i was in your exact shoes like three months ago and totally panicking about spending thousands!!! Playing it safe seemed smarter because i was terrified of dropping three grand and then hating the weight of the gear... basically i grabbed the Canon RF 100-400mm f/5.6-8 IS USM first just to see if i actually liked birding before committing the big bucks. it is seriously so light and cheap compared to the L glass and it surprised me how sharp it is on the r7! since you have 2500 saved you could literally buy that and maybe even the Canon RF 800mm f/11 IS STM for when you need crazy reach and still have a ton of cash left over for your trip lol. hiking with the 100-400 is amazing because i dont feel like a pack mule. might be worth trying the budget route first just to see what you actually use... just my two cents tho!!

honestly, that r7 sensor is kinda picky about glass because of the high pixel density. i've been through this and you gotta be careful with that f/9 aperture on the big zoom. if you're under a thick canopy or it's a cloudy morning, your iso is gonna skyrocket and the noise gets real ugly. leaning toward the safer bet is probably smart since you have the cash saved up...

• the Canon RF 100-500mm f/4.5-7.1 L IS USM is just built better for the field. it’s an L lens, so the weather sealing is actually reliable if you get caught in some rain.
• reach on a crop body is already 1.6x, so that 500mm is basically 800mm equivalent. that’s usually enough for most birds unless they're super tiny and far away.
• make sure to check the weight too. the 100-500 is way easier to handhold for a few hours than the 800mm monster. sticking with the L glass for the trip is my advice. it's just more consistent and the colors are way better. the Canon RF 200-800mm f/6.3-9 IS USM is tempting for the reach, but f/9 in the woods? man, that's asking for trouble. you'll end up with a lot of grainy, blurry shots when the sun isnt blasting. grab the 100-500 and maybe look into the Canon Extender RF 1.4x down the road if you really feel the itch for more range... but you probably wont even need it.

Ive spent the last year really digging into the R7 for birding and i gotta say, im incredibly satisfied with the results despite the learning curve. That sensor is dense as heck and demands a lot from your technique, but when things click, the detail is unreal. My experience has been that reliability in autofocus matters more than anything else when youre chasing warblers in the shadows. To give you a better steer on the glass, i had a couple things i was curious about:

• What are the lighting conditions usually like at your local reserve, mostly open water or deep canopy?
• Are you okay with using AI-based denoise software in your post-processing workflow? Knowing those bits would really help narrow it down because i found my own preference shifted once i started using better software to handle the higher ISOs.