Preheat oven to 450°. Remove giblets from chicken cavity and discard; pat dry with paper towels. Place chicken in roaster pan; sprinkle ½ tsp salt and ¼ tsp black pepper inside cavity. Cut lemon, orange and grapefruit in half; squeeze juice from fruit over chicken and inside cavity. Place lemon, orange and grapefruit pieces, and thyme inside cavity; brush chicken skin with 2 Tbsp oil, and sprinkle with 1 tsp salt and ¼ tsp black pepper. Tie legs of chicken together with kitchen string; roast 30 minutes or until outside is browned. Reduce oven temperature to 375°.
In large bowl, toss potatoes, carrots, fennel, and remaining ½ tsp salt, ¼ tsp black pepper and 1 Tbsp oil; spread around chicken in pan. Roast chicken and vegetables 1 hour 20 minutes or until thermometer inserted into thickest part of thigh reaches 165° and vegetables are tender. Let chicken stand 10 minutes before slicing.
In small bowl, whisk honey and cayenne pepper. Makes about ½ cup.
Serve chicken drizzled with honey mixture sprinkled with fronds, if desired, along with vegetables.