This side of the country we don't have very many ram or hard headed goats that like the heavens, but we do have the Sika deer in the marshes here in MD. Hardest dang thing I've hunted. Small, a stag is only about 100lbs, quiet, dark brown, they blend real well. Not a big critter, but a lot of heart.
Fred....

All NA animals are wimps compared to mtn goats!

Chipmunks - chipmunks    .....little varmits are sooooo small and fast..jump the string all the time...heck they jump at everything..never stand still...darn chipmunks...chipmunks...chipmunks

They will drive you crazy....chipmunks....tee hee

Jer Bear

NO BUT SERUOSLY - it's still CHIPMUNKS.....and minus 28 when you don't feel like going outside and shooting....CABIN FEVER...CABIN FEVER dudes and Dudettes....Please warmup..please...friggin chipmunks    

Jer Bearly

I have to say coyotes.  I have never been able to get off a shot at those wiley critters, maybe once years ago when I saw my first one.  

I have seen them circle to pick up my wind or I have been busted by their amazing eyesight nearly everytime.

The only other time I could have killed one, I was in my treestand and just about to haul my bow up in the gray light of morning.  It came directly under my stand and peed next to my bow and sat down for a few minutes.  What brazen gaul.  Not a thing I could do.  Each time I encounter one and walk away without a fur, I become more intrigued by them as game animals.

Going with the idea of "toughest animal", as opposed to "toughest hunt", I would unequivicably go with the guys that said squirrels. I've squared one in the back with a 60# bow and 650gr arrow and it pop back up and run off, and I've had to put multiple hits on some to kill them (several times). Then of course, half the time after you put one down it's not down for the count, and you end up in a foot chase and then having to go hand to hand with the beast to bring it to bag...     I've always said that if fox squirrels were half as big as a whitetail, nobody'd ever be able to kill one.

your tree rats     still aint got one maybe next time i come over man they are more fun than a barrel of monkeys

sandhill cranes, eyes as good as any animal

squirrels tough little critters

Toughest to kill....tree rats. I shot one with a Muzzy three blade with new, sharp blades about 4 years ago. He was at the base of a pine an made it up about 75' before he expired. I didn't get my arrow back til the next Spring when the other carnivores and decay allowed it to fall to the ground. I know when Ben Pearson thought up the Deadhead he was thinking about turkeys but I have a feeling  squirrels is where his subconscious was.

Bighorn sheep was  my toughest hunt, the sheep won hands down.

A big mature Mule Deer can be a pretty tough nut to crack, after that, a Coyote!

eastern turkey!!!