Howdy,

Hard to say how you can easily replace the Really Big Long Fast lens other than perhaps one of the newest prosumers with fixed-aperture zooms e.g., Panny FZ1000. Am guessing the 500mm alone is several pounds and demands a tripod to boot.

More prosaic than DSLRs in terms of lens selection are the mirrorless system cameras. Last few seasons I've been carrying an Olympus OM-D with two or three lenses and a small stack of batteries. Before that it was an advanced compact, basically since my film days--ounces instead of pounds.

Here are shots from August with the E-M1+12-40/2.8 or 40-150/4-5.6. The camera and 12-40 are weatherproof, which proved useful.