Hawks have good eye sight it could be a sage mode just to boost his visual powers
and this third sage mode place was mentioned in Sasuke's story segment and Bro Hawks live in Rain forests which is also damp go and google it : )
No, it was mentioned in Kabuto's story...
If you'd knew more about the slugs you would understand.
As we all know Shikkotsurin literally means "Damp Bone Forest".
Now, what do we know about Slugs, generally?
The soft, slimy bodies of slugs are prone to desiccation, so land-living slugs are confined to moist environments and must retreat to damp hiding places when the weather is dry.
Now why I assume the Bone Forest is related to?
Well, slugs are somewhat snails without the shell, like a human without its bones and well the forest is the perfect damp environement.
if Tsunade had Sage mode she would have used it on Madara and she never did....because he left and Also Hawks live in The Forests as well to get their prey you can google it or Wiki it plus Sasuke is more important than Tsunade my friend
It seems you missed the part where when Tsunade saw Madara taking out the Perfect Susanoo she was preparing to do a hand seal.
And who says that he is more important? Keep your fanboyism home, boy. He's not the only one in this story.