Weight doesn't tend to be a limiting factor for swimmers. Hence blue whales. It does tend to be a limiting factor for fliers (hence hollow bones, etc). The hea

Weight doesn't tend to be a limiting factor for swimmers. Hence blue whales. It does tend to be a limiting factor for fliers (hence hollow bones, etc). The heaviest flying creature on Earth does not exceed about 40 pounds. Including extinct animals, the heaviest flier was not more than 550 pounds. A blue whale can weigh almost 1,000 times that.