How do migratory birds mange to fly non-stop all the way to their breeding ground thousands of kilometres away?

In preparation for their arduous journeys many migrant birds accumulate generous deposits of fat shortly before embarkation—as much as 50 per cent of total body weight in case of some birds. This fatty fuel is primarily in the form of high-energy triglyceride, which is different from structural body fats. A clear evidence of the role of fat as a fuel for migration comes from studies of the weights of migratory birds before and after they cross a large and hostile environment where feeding would be impossible. One banded North American bird belonging to Turn-stone species (photo above), flew from Alaska to the Hawaii Islands in 4 days, averaging over 1,000 kilometers per day. It weighed 174 grams when banded and 154.8 grams when recaptured—a loss of 19.2 grams. This is equivalent to flying 100 kilometers on just 1/2 gram of fat. An equally impressive long-distance travel-ler is the tiny Ruby throated Hummingbird (photo, below). Weighing about 4.5 grams of which 2 grams is fat, it can fly non-stop for 26 hours, consuming the fat at the rate of barely 0.69 calories per hour. At an average speed of 40 kilometres per hour, the bird's flying range would be about 1,050 kilometers easily enough to span the Gulf of Mexico!