Quantitative methods of estimating flight range instead look at metabolic rates of the bunting and how much fat it has to use as fuel. Research indicates that the metabolic rate of a lean 13 g Indigo Bunting is 0.64 kcal/hour. With an average speed of 20 mph, 5 extra grams of fat (47.5 kcal of energy) extends a bunting’s range to 688 miles. 19 grams is equivalent to 826 miles. Given that the trip across the Gulf of Mexico from Florida is approximately 600 miles, Buntings weighing at least 18 g could make the trip without any stops.