Squirrel #18: Cave Dweller
As soon as the track starts, you need to accelerate and bunny hop forwards to jump out of the lift onto the pipe ahead.
This will then allow you to drop backwards onto the roof of the lift, before reversing onto the platform to the left of it.
After landing on the platform, the next squirrel will appear.
Squirrel #19: Covert Ops
A surprisingly easy one, this--simply finish the track and wait after falling into the hole.
After a few seconds the penultimate squirrel will ride into shot on a platform.
Squirrel #20: Jungle Gymkhana
Keep an eye out for the rotating colour panels behind certain checkpoints, then ride forward when the combination you want has moved into position. For the first one, you want the top section to be Red + Blue.
At the next panel, you want the middle section to be Green + Red.
The final panel needs to read Yellow + Blue on the bottom section, though this may already be locked into place when you get there.
Now finish the track to collect the final squirrel, along with the Bright-Eyed %26 Bushy-Tailed Trophy/Achievement--congratulations!