Well - you asked for it! Here are a few ideas. Don't know if they're feasible, but it gives something to think about.
CAMOUFLAGE
* Similar to burrowing & hide (I don't think we need too many skills that essentially do the same thing (namely raise defence). The difference is that is raises ATT & DEF, and costs less turns to spy. Perhaps, like Hide, it could hide the ? on neighbouring provinces.
* Cost about 100 (because it does a lot of things)
* I don't think you need any prerequisites at all (may BP 2 if you really need to restrict the new skills)
* Why is it Cool?

.... 'cause it would probably increase the use of spying. Also, it shouldn't need any major changes to the game engine (as burrowing would)
* extra comment: as said above, I don't think we need heaps of skills that do essentially the same thing. I think we could consider Hide, Burrow or Camouflage, but not all. I simply offer this as an alternative to the others.
COURTSHIP
* improves fertility about 3%
* Cost 100 skill points
* at least 4 appendages (could be 3 legs and 1 arm, or 4 arms and no legs) and half a brain
* Why it's cool?

If you need to ask that question you probably should get out more.
HIBERNATION (or SIESTA)
* lowers loss of saturation for large animals, but at a cost to fertility. Not sure how much effect - let's say saturation loss each step is halved, but births are halved as well
* cost: dunno --- 50? 80?
* body size 4
* Why is it Cool?

It's just not cool to eat all the time. I'd rather spend by time drinking or sleeping

... or bushwalking. .... spying on the neighbours doing their camouflage and courtship rituals
SCAVENGER
* gets more saturation out of every feed (say 20% more) when hunting another species
* cost: dunno --- 70?
* must be omnivore or carnivore
* Cool?

It's not cool at all to be a scavenger - just a fact of nature.
RAID
* raids a neighbouring square to hunt plants or a species (only perform half the number of attacks compared to normal)
* cost: 50?
* prerequisite: 2 legs
* Cool?

This would be an active skill - rather than "passive" skill like all the above (ie. passive ones just raise or lower a species' attribute, while active ones introduce a whole new action they can undertake).
RETALIATE
* inflicts damage when another species attacks you, eg. when attacked, each failure on the PATT/PDEF gived a 25% chance to kill a specimen of the attacking player
* cost 50
* prerequisite: 3 Brain power
* Cool?

Makes attacking a bit more dangerous. Would promote spying first instead of just attacking.
That's all for now.
Have fun, everyone.
Goat herder
Live long and prosper ---- but don't let the Taxation Department know.