And what are today’s birds telling us? The Audubon Society estimates that nearly 60 percent of 305 bird species found in North America in winter are shifting northward and to higher elevations in response to climate change. For comparison, imagine the inhabitants of 30 states — using state residence as a proxy for species of American human — becoming disgruntled with forest fires and drought and severe weather events, and seeking out suitable new habitat.

The Audubon Society’s estimates rest largely on data supplied by volunteers in citizen-science projects like the Christmas Bird Count (first proposed in 1900, nine years after the first known use of the word “bird-watcher,” to set the hobby apart from the more traditional Christmas pastime of shooting birds). The birds in question have shifted an average of 35 miles north over a period of about 40 years — seemingly insignificant in human terms, but a major move ecologically.

Such documentation, drawing on databases and the practices of citizen science, is descended from folk wisdom, where birds are ascribed a certain predictive power. Folk wisdom holds that they nest high in anticipation of warm weather (not true) or fly low when they expect to get wet (true).