Check exactly what type of aircraft you are flying on. Embraer ERJ 170s and 175s (65-76 seats) have bins large enough that most normal-sized carryons will fit. E145s and CRJ-200s (50 seats) are tiny with tiny bins and almost no normal-sized carryons fit, they are usually valet checked and given back on the jetbridge. CRJ-700s and CRJ-900s (65-79 seats) are somewhere in the middle and smaller rollarboards may be OK.

If more than one regional jet flies to your airports and you are able to switch flights to one operated by an ERJ 170 or ERJ175 or a mainline aircraft (Airbus, Boeing) you will be much better off.

I travel with a Backlight 26L camera bag and it fits under airplane seats. If your lenses are small, you might be able to get three camera/lens combos in one. Then you might be able to fit the other three into a smaller rollarboard.

Well clearly you’ve never shot birds, without long focal lengths most wild birds will be tiny in your frame.