Some of the most compelling stories belong to migratory species, according to Townshend. The Beijing swift, for instance, nests in the city's ancient gateways and temples. Recent tracking studies revealed they fly all the way to southern Africa and back, a journey Townshend hopes to prove is made without landing — meaning the birds eat, drink and sleep while flying for months.

Another astonishing story belongs to the bar-tailed godwit, a shorebird that flies nonstop from Alaska to New Zealand. To prepare for the long flight, it shrinks its own digestive organs and doubles its heart size, transforming, in Townshend's words, "from an eating machine to a flying machine".