The Dominant Singers Alongside The Insects

Psychologist Eleanor Ratcliffe and her colleagues found that familiarity of timbre and melody are predictors of how restorative we find birdsong. Andrew Whitehouse’s surveys found that Australians living in the United Kingdom hanker for the sounds of their former home, sometimes playing recordings to awaken aural memories. The power of bird sounds to forcefully evoke in us feelings of alienation or belonging is partly a reflection of how divergent the sounds of different continents can be. These feelings are also reminders that the sounds of other species are lodged deep within us, carried within our subconscious as aural compasses, orienting us toward home. Summaries belie inner complexity. After all, every habitat has many sonic variations and textures. Walk a kilometer or two through any forest and your ears will encounter variegations of tone and rhythm from the combined voices of sometimes hundreds of species. Some of this sonic diversity emerges from the varied physicality of the world. Earth has many forms of wind, mountain, rain, wave, beach, and river. Raindrops are larger in the Amazon than in North American skies. Northerly coastlines retain the mark of scouring glaciers, and their rocky headlands have more assertive voices than the sands and muds of unglaciated subtropical shores. Rivers meandering through continental interiors are slurred and languid compared with water coursing down mountain slopes.

We All Die Someday

The geologic history of the world has created varied surfaces and flows for unvarying physical laws to play against. Evolution adds two more creative forces to this global diversity of sound. The happenstances of history have populated different regions with varied branches of the tree of life. Each branch has its own stories of origin, migration, species diversification, and extinction. Combined, these stories yield diverse geographies of sounds. Overlain on this, every species experiences its own path of aesthetic innovation and sonic adaptation to place. Over millions of years, divergences scale up to give whole regions different sonic characteristics. A raindrop of a given size makes the same sound whether it lands on rock in America, Israel, or Australia. The songs of animals in these places, even species of very similar sizes and ecologies, cannot be deduced from physical law. History and the quirks of animal communication add delicious layers of contingency and caprice to life’s voices. On any place on Earth, we hear the voices of both indigenous and colonist animals. When we look back tens or hundreds of millions of years, we find that the modern distribution of every group of animals results from some species cleaving to home and others striking out for new land.

Full Circle

A few of each type then split into new species, producing a rich tangle of geography and taxonomy. It is not surprising, then, that the sounds of crickets today are so similar among continents. Each place inherited crickets from a singular landmass that then split. But crickets are hardy too, and can withstand ocean journeys on floating vegetation. Some of the unity we hear is the result of more recent dispersal. A similar pattern of ancient unity and more recent colonization accounts for the distribution of other singing insects. Katydids or bush crickets likely originated on the southern supercontinent Gondwana, one of the landmasses formed when Pangaea broke apart. They then repeatedly jumped among landmasses, producing a family tree with close cousins on different continents. The marbled bush cricket that I heard in Jerusalem belongs to a clan that invaded the temperate regions of Europe and then North America from Australia. The common katydid that pounds the night air on Saint Catherines Island belongs to a different branch of the family tree, one that colonized the Americas from Africa. Cicadas also have a global distribution, their present form dating back at least to the time when Pangaea broke up. Since then, they have repeatedly jumped among continents, with close kin on widely separated landmasses.

A Better Day

The periodical cicadas of North America, for example, are taxonomic cousins to some Australian cicadas. The ancestry of most living frog species is also rooted in Gondwana. There, two main branches formed. One, on land that would become Africa after Gondwana split apart, led to the pond frogs, Australasian tree frogs, and narrowmouth toads. The other, South America, gave rise to all American and European tree frogs, toads, and Australian ground frogs. To this day, South America and Africa are home to the majority of frog taxonomic families. Away from these centers of origin, we mostly hear the few families that managed to cross oceans and colonize new lands. One descendant lineage led to the modern parrots and the other to modern songbirds. Combined, these two branches of the bird family tree comprise more than half of the nearly ten thousand living bird species. In many soundscapes, they are the dominant singers alongside the insects. The extraordinary sounds that I heard at Crowdy Bay, then, are rooted in the evolutionary homeland of songbirds. Cockatoos and parrots, common birds all over Australia, have lived here since their ancestors split from the songbirds. The lyrebird stem of the family tree dates back nearly thirty million years, and its complex song is evidence that ancestral songbirds were accomplished singers. The sounds we hear outside of this region are elaborations of the legacies of small groups of emigrants, dispersing birds whose descendants produced marvelously diverse soundscapes across the world. The first wave populated Asia and then the Americas but left no living descendants in the Middle East and Europe. The second wave founded a lineage that now comprises more than half of all living songbird species. A few of these bird families also came to the Americas. But American soundscapes owe much of their character to the flourishing of just one offshoot of this second wave. Biologists long assumed that Australian animals and plants originally came from Asia, side branches of a story that they believed was firmly rooted in the Eurasian landmass. Old World, New World, Oriental, and Antipodean, as if geologic time and the tree of life were rooted in northern Europe.