Not all the eggs hatch, but few go to waste. A source of valuable fat and protein, the eggs fuel the next 2,414 to 3,219 kilometers (1,500 to 2,000 miles) of the birds' northward journey to the Arctic tundra. "Even though the eggs themselves are not necessarily more nutritious than other kinds of invertebrate prey, it's their sheer abundance that makes it profitable for the birds to spend their two weeks or so feeding here," explains Dr. Mark Botton, associate professor of biology at Fordham University. Each year 80 percent of the North American population of red knots, for example, stops over on the egg-rich beaches of New Jersey and Delaware. Red knots arrive underweight after the 11,265-kilometer (7,000-mile) flight from southern Brazil, and they can come close to doubling their body weight during their ten-day to two-week stopovers. (Imagine a one-hundred-pound/forty-five-kilogram person gaining doubling his weight over spring vacation.)