My reading habits do not change all that much during the summer.
I don't read more outside - living where I do means that for it to be warm enough for comfortable outside reading it has to be sunny, and I burn easily. I do love to read on my living room sofa with the balcony doors open and a breeze wafting in the sounds and smells of summer. Only yesterday I was reading and the room was filled with the heady scent of newly mown grass - wonderful!
Neither do I exchange brain food for brain candy in the summer - my reading is always an eclectic mix of both - but I do tend to read shorter books and to reread more.
My summer reading sessions are shorter than the winter ones: I will read a chapter, then go and do something else; but there are also more of them, so I don't really read any less than I do in the winter.