Skeery cow elk or Nordic Sika call. The Nordic is really loud, best thing is to sound big enough to be a threat but small enough to have the snot knocked out of you. They can come in from quite a way off and have a habit of standing 2-3 yards back in heavy cover checking things out, all you see are eyes or antlers, they're also really sneaky and quiet.
They will also absolutely lock down on your position from a long long way out. I've managed to get a response from 3rd week of September through til middle of December. Mind you, if a stag already has hinds the response can be to herd them as far away as possible at warp speed.
Try not to shoot them all, they can be very vulnerable.