So I'm not sure if the locations of ability capsules have been documented yet so just in case I took a screenshot of where I found one.
http://gyazo.com/7cd04541a31f914f63d45d8f8ab8f3ef this is in an area when you surf left in the goldenleaf forest pond.
This may be a stupid thing to ask but I've explored the hell out of akora forest and can't find a tree to headbutt. I've made it past the kingdra but still can't find it, any hints?