The Heaviest Owl in North America

I learned from Cornell Labs’ All About Birds site that the Snowy Owl is the heaviest bird in North America, “typically weighing about 4 pounds—one pound heavier than a Great Horned Owl and twice the weight of a Great Gray Owl (North America’s tallest owl).” Here, I also learned that the Great Gray Owl is the tallest owl in North America (two-for-one learning). What makes the Snowy Owl so heavy (it’s relative)? “Thick feathers for insulation from Arctic cold make Snowy Owls North America’s heaviest owl…” It is certainly bigger and bulkier than the dimunutive saw-whet owl, which I once covered on The New Leaf Journal.