I highly recommend Norman Del Mar's authoritative three-volume study of Strauss, published in the US by Cornell University Press. He draws the links to Mahler (especially the cow bells in the Alpensinfonie). I've always felt Strauss did himself no good by calling attention to himself as a "musical realist." In every major work, there's at least one passage that has nothing to do with realistic depction. He's a Romantic, just as Mahler was. Steve Schwartz