Songs in which the singer (or someone else) whistles are an acquired taste. Most of the time, it's a cheap gimmick, that drives me mad (example). Sometimes, it fits (example). Sweet Emily Loizeau has made a jazzy folky song (part French, part English), for her upcoming new album Le Pays Sauvage, that shows that yes, you can make whistling add to the summer's day atmosphere. Looking forward to that album (in February) very, very much. But please, don't whistle too much.
Emily Loizeau - Sister