Time is short for the millions of migratory songbirds that journey thousands of miles north to breed on Alaska’s North Slope. On this vast swath of Arctic tundra, which drops gently downward from the Brooks Range for about 130 miles until it meets the Arctic Ocean, the sun shines around the clock for just a few months, quickening the pace of life. Their arrival and departure cued by that nearest of stars, the birds race for the nesting territory and food they’ll need to raise their young and prepare for the return trip south come autumn.Many of the birds, such as white-crowned sparrows, American robins, savannah sparrows, and Lapland longspurs, are the same ones that regularly visit the Lower 48. When they arrive in the Arctic in late spring, they rely on the dried remains of last year’s bog blueberry and bog cranberry, exposed as the snow melts. Then much heartier meals become available, like spiders, crane flies, midges, and caterpillars. “Just like we don’t want to be...