I htink people routinely help calls to hatch(because of their small beaks I think). I have read that they have a very difficult time and very often need help. I'm sure others will chime in but you might just be having breed difficulties. Oh also, I've never hatched calls in particular but I have hatched alot of 'scovies and a few mallards and I keep my humidity aroun 72 (70-75) is what I shoot for. Why are you trying to get it over 75?