Season split birds liberally with salt and pepper
Whisk together first 3 marinade ingredients in a large bowl. While whisking, add oil in a thin stream. Add remaining ingredients
Place birds in marinade and toss to coat. Refrigerate for 3 to 4 hours, turning occasionally.
Remove birds from refrigerator and drain marinade ingredients into a small saucepan. Bring marinade to a boil, reduce heat and simmer for 3 to 4 minutes. If necessary, add additional orange juice concentrate and lemon/lime juices. Allow to cool.
Grill chukar on a medium-hot grill until just cooked and still a tad pink at the thigh joint. While grilling, baste with marinade.