On Alaska’s North Slope, scientists tread carefully across clumps of tussock grasses toward a fast-flowing stream draining the imposing Brooks Range of ice and snow. Near Galbraith Creek, they string out a mist net for white-crowned sparrows. The birds have recently arrived from southerly latitudes, intent on feasting on the insects that will soon descend on the tundra like storm clouds.The Arctic summer is short-lived, and sparrows have only a few weeks to establish territories, find mates, lay eggs and raise their chicks on a steady diet of bugs. From every ensnared bird, the scientists collect blood, feather and faecal samples to see what they are eating and how that changes over the summer.One thing they want to know is whether the sparrows are consuming a lot of stream insects, such as stoneflies and mayflies, says Ian Shuman, a doctoral student in quantitative ecology at Columbia University. As willow shrubs claim new territory along the Arctic’s rivers and streams – a process scientists call “shrubification” – this could disrupt the life cycles of stoneflies and mayflies. If the songbirds also depend on aquatic insects to thrive, that might affect the sparrows’ prospects.The tundra can feel immutable in its vastness. A sea of grass and moss extends as far as the eye can see. But above the Arctic Circle, change is happening faster than anywhere else on Earth. Snow is melting earlier in the spring, sending torrents of water downstream. By late summer, such early season deluges have given way to parched creek beds. The Arctic grayling – cold water fish in the salmon family – that swim between deep lake winter refuges and shallow summer spawning streams may become stranded in isolated pools. Their survival, too, rests on the mayflies and stoneflies.