customising the text entry fields?

Apologies if this is the wrong part of the forum to ask this- I would like to customise the text-entry areas where users type their post, so that instead of "subject", they can enter "species" in one box and "location" in another box, then the subject header of the post is made up from the post with "species at location" (it is a birding news website). Is this possible to do?

Thanks for your reply. It wasn't just to change the text, however- but to create two "subject" fields, one for species and one for location (to force people to enter both of them) and then combine the two into the heading for the post.