Leopold knows that spring has truly arrived when the upland plover, a type of waterfowl, returns from its migration to Argentina. Although Leopold legally owns the land, he notes that this plover “has just flown 4000 miles to reassert the title he got from the Indians,” and that the land is technically his.
Just as the geese signal that March has arrived, the plover signals that spring is here. The animals and the weather are more important to Leopold than the calendar, which would say spring always begins in late March.
The plover’s migration, in Leopold’s mind, serves to “prove again the age-old unity of the Americas.” Although political and diplomatic unity is relatively recent among humans, birds have been unifying the two continents via their migration for thousands of years.
Just as the geese seem to know what humans do not—how interconnected the world is—the plover helps remind Leopold of what it knows in its DNA, that North and South America, although crisscrossed with political divisions, are united ecologically by the migration of birds.
Leopold notes that the plover has only two natural enemies, the gully and the drainage ditch. However, he also has an unnatural enemy: the hunting rifle. Leopold wonders if humans will realize they also have to fear the gully and drainage ditch, and applauds the (belated) protection of migratory birds from hunting, arguing that “the lure of plover-on-toast” is not worth the eradication of a species, and the silence of plover-less prairies.
Leopold understands what many people do not—that modifications to a physical environment also modify the behavior of the animals that live upon it (humans included). By changing the land through agriculture and irrigation, humans have destroyed many of the watery places plovers formerly called home. In this way, although humans are not actively killing they birds, they are passively contributing to their potential extinction.