He's a harris hawk. As I'm sure you've noticed he's very intelligent. I'm betting he has indeed figured out that you will feed him no matter what he does. That's where the weight management comes in. There's a difference between low and hungry. Usually the two go together but you can lower a bird's weight to death's door without actually making him HUNGRY. Giving a bird several small meals every day will lower their weight but won't really make them HUNGRY. That's where fasting a day or even two works wonders. You want a bird at as high a weight as possible, but low enough they actually GET hungry and want to eat.

In this bird's case, he knows the game, he knows exactly what he has to do to get fed. He ALSO knows he doesn't have to do it if he doesn't want to. I would bring his weight up to a nice fat, healthy weight where he will still come instantly inside to the glove. Make sure he can't see what's in the glove and still comes-it's very important that he can't decide the tidbit you're offering isn't good enough. Vary the size and be sure to jackpot him occasionally when he responds instantly. When he's doing that well, take him back outside and try again.

Again, be sure he can't see what you're offering. If he refuses to come to the glove, don't beg him. Pick him up after a minute and put him away. The mouse went down the hole, he lost his chance. Try again after several hours. Same deal. If he refuses, put him away until the next day. If he's at a good, healthy weight he can go DAYS without eating. You aren't going to hurt him. He's not going to starve himself to death when he knows exactly what he needs to do, he's just not interested. He's not a wild bird, he doesn't have all that fear to overcome at this point.

Don't give him any tidbits before training and only work with him once a day (ie once he's done his job and eaten, leave him alone), you need him to be HUNGRY. Not low, hungry. Tidbits or food given in other situations (ie just to make sure he's fed) will just take the edge off his hunger and get you nowhere.

If he comes instantly outside, don't be afraid to jackpot him on the very first call (if you've got other things to do and don't have much time, this is a handy time to jackpot him like this). If you only give tiny tidbits and call him dozens of times, he might decide it's not worth the effort. If he thinks he MIGHT get a whole meal, just for coming to the glove outside he will be much more inclined to do it. You can't hide a whole quail in your glove of course, but you can hide a tidbit he'll have to pull at and either sneak a large reward into the glove (or just put it there if he's not grabby), or toss out a lure and let him jump down to it, whatever works for you.

To summarize, vary the size and schedule of the rewards and don't be afraid to let him get hungry.