If they have light colored feather shafts, you can see the blood in them. It is very simple; I've clipped the wings of all my calls. You don't want to clip them while they are still growing out...b/c that's when they will have blood in them...but if you wait till they are mostly grown (not quite fully...but close), then you can clip with no problems. I still check the shafts of my calls' feathers before clipping them though (on the black ones they have some white feathers...so I just checked the white ones...they all grow at a similar rate), just to make sure there's no blood.