Oversight.
Any window in a Montana that slides open has screens. There are a couple (2 in my 2007 3400) that are "Emergency Exits" that don't have screens, but I it doubtful that those two small sliders in yours are designed for any type of emergency exit.
Except maybe for Rich's bird. But, based on his previous posts of the last year and a half, I don't think he's that concerned about an emergency exit for "the bird that hates him"...