"X flies more highly than Y" or X flies higher than Y?"

Question

Which one is correct?

An eagle flies more highly than a sparrow.

Or

An eagle flies higher than a sparrow.              

Answer 1

The second one is correct. "highly" has another meaning that does not fit here.

Answer 2

the 2nd one seems true. highly means in a higher position but more highly means more intensely/severely/strongly.

Comments

I have to say altitude is the purpose here. Considering this, can we certainly comment which one is grammatically wrong?


Thank you