I recently visited Khao Yai National Park in Thailand. Experience from my trips to Alaska had taught me that adding a wide-range, super-telephoto zoom lens to your big prime will get you that level of versatility you need to capture those furry little (or big) creatures, especially when jumping and running around.
So for the first time, I left my trusted 70-200 f/2.8 zoom behind and took my brand new Nikon AF-S 200-500mm f/5.6E ED VR with me, next to my 600mm f/4 FL. Obviously nicely tucked in a LensCoat lens cover! (no, still not getting paid by them…)

Nikon AF-S 200-500mm f/5.6
When we came across a group of macaques, the 200-500mm proved to be very versatile indeed. I had started shooting with my 600mm f/4 FL on my Gitzo tripod (yes, in ‘Sport’ mode!) but soon wanted to take some shots from within the group. Luckily it seemed they were used to people – apparently – so I was able to shoot from anything between about 5 and 20 meters, a perfect range for the 200-500mm, attached to my Nikon D750.

Nikon 200-500mm f/5.6 on Nikon D750, f/6.3, 1/250 s. ISO 1000, -0.7 exp. corr.

Nikon 200-500mm f5.6 on Nikon D750, f/5.6, 1/400s. ISO 640, -0.7 exp. corr.
The 600mm f/4 was performing perfect on my tripod with VR in ‘SPORT’ mode:

Nikon 600mm f/4 E FL on Nikon D4S, f/4, 1/320 s. ISO 400, -0.3 exp. corr.
But sometimes I needed the range of the 600mm f/4 FL while trying to ‘catch’ fast-moving gibbons high up the trees, which turned out to be almost impossible. I was very lucky to get this one; I was shooting hand-held, with VR set ‘NORMAL’:

Nikon 600mm f/4 E FL on Nikon D4S, f/4, 1/320 s. ISO 4000, +0.3 exp. corr.
And now for something completely different! :)
On the last day of my trip, my guide spotted a large croc on the other side of the river. While I was bing sucked dry by a million or so mosquitos, I carefully set up my tripod, positioned by D4S and 600mm f/4 FL and started shooting. Meanwhile, the croc just went about its business, which was pretty much nothing other than lying down and taking a nap, or so I thought. I decided to add the new TC-14E III teleconverter to give me 850mm @ f/5.6 and saw my little croc was perhaps just as interested in me as I was in him.
To give you an idea of the incredible range 850mm gives you, I also shot the overall scene with my iPhone:

Croc with iPhone …hint: near the river, mid/left of the image
And now…:
iPhone vs. Nikon 600mm f/4 E FL + TC-14E III on Nikon D4S, f/5.6, 1/320 s. ISO 400, -0.7 exp. corr.:

I… See… You…!