We were taking a walk in our neighborhood recently just as dusk was approaching. At the beginning of the walk we heard a chipping sparrow trill; a northern cardinal gave its repeated whistled notes, and a mourning dove its gentle, low “who, who, who.” But as it got darker, each of these bird sounds faded away and disappeared. Almost in the blink of an eye, all that was left was the songs of robins echoing around the yards and streets. The songs included the regular, caroling sing-song we’re all so used to from robins, but most of the voices veered off into high-pitched, thin, very quiet songs. Some added in robust “chup-chup” notes like they tend to do when they are alarmed.

Suddenly it seemed as though there were robin sounds coming from all directions and from more than a dozen birds. And then as darkness was full on, all of the songs ended.

Most of us are familiar with the sometimes-overwhelmingly loud burst of overlapping songs of birds at dawn, appropriately called the “dawn chorus” by ornithologists. The dawn chorus in our area is a late-spring and early-summer phenomenon that last an hour or so each morning (although many birds will continue to sing robustly much longer than that). Typically one of the first bird species to sing each morning before the dawn chorus even gets started are the same ones that are the last ones to sing at night: robins and other thrushes.

Some birds have specific and different songs that they sing only or mostly right at dawn. Many of the flycatchers have such “dawn songs,” and many warblers tend to sing a particular type of song only during those early dawn hours.

But fewer birds are known for singing strongly at dusk, the thrushes being the most notable. Around much of mid-coast Maine, one of the most-loved dusk singers is the hermit thrush. Each song of the hermit thrush starts with a long, lonely, single flute-like note followed by an ethereal echoing of fluty notes that seems to shimmer and then disappear into the air. On a still night down near the water one may hear these beautiful songs floating across a bay from a nearby island or peninsula—the last songs before the summer night closes in.

Here in Maine, the veery and wood thrush are also known to sing before dawn and at dusk like the robin and hermit thrush. Surprisingly, despite the fact that this behavior is well documented in many thrushes, little is known about why thrushes may have evolved to take up the quieter air space before dawn and at dusk. Some scientists have suggested that thrushes have eyes that are more sensitive to light and are stimulated by lower light levels than other birds. But such an observation explains nothing about why they and not other birds might have evolved such a sensitivity and why that would also translate into singing earlier and later than other birds.

Like so many mysteries of the natural world, we humans will continue to enjoy the lilting evening songs of the thrushes around us even if we never find out why it is they are the last to sing.

Jeffrey V. Wells, Ph.D., is a Fellow of the Cornell Lab of Ornithology. Dr. Wells is one of the nation's leading bird experts and conservation biologists and author of the “Birder’s Conservation Handbook.” His grandfather, the late John Chase, was a columnist for the Boothbay Register for many years. Allison Childs Wells, formerly of the Cornell Lab of Ornithology, is a senior director at the Natural Resources Council of Maine, a nonprofit membership organization working statewide to protect the nature of Maine. Both are widely published natural history writers and are the authors of the popular book, “Maine’s Favorite Birds” (Tilbury House) and the newly released “Birds of Aruba, Bonaire, and Curaçao” from Cornell University Press.