Looking for a needle in a haystack

Researchers spread out to comb the tundra in search of a single bird: a dunlin that is wearing a small backpack, carrying a transmitter that has collected a record of movement over the past year. The bird was sighted but not recaptured, since it didn't have an active nest to return to. The dunlin is a small shorebird, small enough that it can't wear one of the larger transmitters that can send a location signal in real time.