Two birds meet in mid-flight, one heading east and one west, and chat about what lies ahead. The westbound bird says there is nothing but the nests of "the old human race," who are dead. The birds rest, wonder about these vanished beings, and guess at them in birdlike terms: builders like ants, walking on two legs, possibly not even laying eggs. Neither knows how humans died, and neither expects anyone ever will.
The tone starts gentle and almost comic, with its chirpy small talk and its bird's-eye misunderstandings. Then the eastbound bird reaches the city, and the mood shifts. The "tall, tilting tombs" of concrete and steel loom over it, and it has no words for what it sees. The poem seems to suggest that even a great civilization can end up as something nobody understands. The final feeling is of being "fleeting and small and alone," a quiet, humbling awe.