Question about Fenway

Hi All,

I've never been to Fenway for a game (I live in Texas) but I was hoping someone could answer this a question about it for me.

I was looking through the 2015 Red Sox Media Guide and it mentioned the seating capacity for night games was 37,673 but the seating capacity for day games was 37,221. (See page 13 of Media Guide.)

What causes the difference of 452 seats?

Direct Link to Media Guide PDF Download