Having used a combination of what's suggested here; my options would be: -
1) 70-300 VR, if you're on limited budget (can be bought for the price of renting the 200-400 VR)
2) 70-200 VR II with the 2x TC E-III, pretty sharp even with this new 2x TC. You'll lose a stop over the 200-400 VR; but this option gives you a wider range to play with, and is more hand-holdable
3) 200-400 VR, an impressive range, and sharpness; but it's bulky, big, weighs a lot, centre of gravity is too far in front of me (I'm 5'10"). I love it with the 1.4x TC, but if your needs are only unto 400mm i see option #2 more suitable?
Whichever way you go, you'll need to practice a lot to get the rhythm with such long focal lengths. It's easy to forget, use relatively slow shutter speeds and end up with camera shake that even the VR can't compensate for.
Beanbag, an excellent tool for all three options
Oh yes, practice some more; can't stress this enough. If you're renting something, then rent it out for a couple of weeks before the trip for good practicing, cheeper than having to go back and reshoot
Lens for hire are members on here. Beanbags, another member here sells some gvery good ones.