Paul - I used to have a canon 70-300 which is a pretty good all round lens, you could look for one of those as that would cover the full range that you need to avoid any lens changing in the field which would eliminate the risk of dust getting in during the changeover, something which I am now paranoid about following several camera cleans

I know what you mean about the 100-400 being a bit borderline at Myrtle Ave / Cains Lane.
Otherwise as another suggestion I now have a sigma 18-250 which is even better as an all rounder alongside my 100-400. When I go abroad I only take the 18-250 and am pleased with the results, I find the 100-400 is a bit much to cart around on aeroplanes! The 18-250 is very flexible as an only lens, might be worth thinking about.