AUCKLAND, New ZealandIt takes 12 minutes to walk across Auckland at its narrowest point.

Let me elaborate. The North Island of New Zealand, of which Auckland is the largest city, looks like a fish with its head pointing south. At roughly the base of the fish’s tail, two decent-size bites have been taken out of each flank, leaving two harbors. Central Auckland fills the isthmus in between.

A river slices inland from the city’s eastern side, and at its farthest reach I survey the discards of suburbia: tires, engine parts, dead TVs, traffic cones. The tide is full, and a dull sheet of water soaks the mangrove stems. A swamphen—two-tone body, blue and black, outrageous scarlet bill—struts toward a grassy island,