[...] guano accumulated only in extremely dry climates, oceanic deserts where the lack of rainfall allowed bird droppings to collect for centuries. Such islands were barren rocks, not fertile plains—unpromising sites for human habitation.

Still, the guano didn’t hop onto the ships by itself. Guano mining—tunneling, picking, and blasting the stuff loose and hauling it to waiting ships—was arguably the single worst job you could have in the nineteenth century. It offered all the backbreaking labor and lung damage of coal mining, but to do the job, you had to be marooned on a hot, dry, pestilential, and foul-smelling island for months. Respiratory diseases, causing workers to pass out or cough up blood, were common. So were gastrointestinal ailments—the unsurprising consequence of crowded conditions, rotten food, and a dearth of fresh water. Clouds of shrieking seabirds darkened the skies overhead, unleashing the occasional fecal rainstorm (“We were completely encased in a thick film of bird manure,” one visitor remembered). On Howland Island, an out-of-control rat population scurried underfoot, adding yet another vile ingredient to the epidemiological stew.

Finding workers wasn’t easy. Peruvian guano lords, unable to recruit their compatriots, relied mainly on Chinese laborers, whom they lured onto eastbound ships with false promises or sometimes simply kidnapped—between 1847 and 1874, at least sixty-eight of these ships mutinied. U.S. guano speculators gathered their workforce principally from Hawai‘i, where, it was felt, the workers (called “Kanakas”) would have some affinity for the landscape. [...]