When a parenthetical phrase or sentence interrupts the middle of a sentence, do not capitalize the first letter inside the parentheses unless, of course, the word is a proper noun or proper adjective.
Example: We saw Roseate Spoonbills (they have an exquisite pink color) on our trip to Texas.
The first letter in a parenthetical question or exclamation is always capitalized.
Incorrect: We saw Brown Pelicans (have you ever seen one?) along the shore there.
Correct: We saw Brown Pelicans (Have you ever seen one?) along the shore there.
A parenthetical sentence that goes between two sentences of text uses both an initial capital letter and an end mark (period, question mark, or exclamation point) inside the parentheses.
Incorrect: We took a trip to Texas. (it is a big state)! There we saw many Brown Pelicans.
Correct: We took a trip to Texas. (It is a big state!) There we saw many Brown Pelicans.
In a sentence containing a parenthetical expression, any punctuation belonging to the main sentence goes outside the parentheses.
Incorrect: It was a real heat wave (five days over 100°!)
Correct: It was a real heat wave (five days over 100°)!
Correct: We saw Jerry, Ed (Tom's brother), and Julius there last night.