As I have aged, my exploration of wildlife is dependent on listening as much as watching. I often close my eyes to hear the “voices” of birds, insects, mammals, amphibians, and the fluttering wingbeats, woodland rustles, and wetland splashes of their activities.
But, in recent weeks, my early morning walk with Jessie the dog has featured a changing soundtrack. The peepers have stopped chirping in the wetlands. The green frogs no longer “garumpf” from the ponds. Most of the songbirds (Passerines) have finished their season of melodic courtship and territorial assertion, and some have silently packed their bags for the southward migration.
Where Did All the Music Go?
A few bird species eagerly sing into September as they prefer to schedule a delayed breeding season. Late breeding American Goldfinches voice their bouncing melodies while taking advantage to feed on the weed seeds. Similarly, Cedar Waxwings, with their high, wheezy voices, can be heard as long as their late summer wild fruits are available. Some Passerine species may produce a second or even a third brood, which keeps them singing as the summer lasts on. For example, the chattery House Wrens, our iconic songster American Robins, and the seemingly carefree Eastern Bluebirds will all sing into September as long as they have young in their presence.
Long ago, ornithologists working in temperate climates noticed that most Passerines for some reason have a second round of singing in mid-summer. The theory that emerged was the solar calendar. The spring breeding season features the songs of warblers, sparrows, thrushes, and many more to declare their breeding territory and win a mate. During that frenzy of breeding, day length increases until the summer solstice. But after the solstice, as the day length diminishes, are male Passerines stimulated to sing again when that day length is the same as it was in late spring? This theory has not been proven right or wrong, but more convincing evidence suggests that singing after the breeding season is instructive. Most Passerine songs are voiced by males, and most young Passerines must learn their species’ song from their fathers or other males.
These students of song are lots of fun to hear in late summer. I awake each morning to juvenile Hermit Thrushes who sing a ragged version of our state bird’s renowned flute-like song. Flat and out of tune, young White-throated Sparrows have yet to master the sweet pitch and clear, pure notes of “Poor Sam Peabody” or, further north, “Oh, Sweet Canada.” Music school for White-breasted Nuthatches sounds more like playground recess, and our gathering Blue Jays must convey an elaborate curriculum to their squawking youth.
Bird song researchers have defined three stages of song learning:
Sub-song, which is mere voice, like a toddler’s first efforts at words
Plastic song, when they get the right notes but explore many different combinations (like my juvenile Hermit Thrushes)
Crystallized song, the locked-in mastery of adult song. This progression begins with nestlings and fledglings, continues through the presence of adult male “teachers,” and is usually completed by the next spring.
Late summer is also the season of another kind of symphony, that of the crickets and katydids. These insects do not play wind instruments; they are more akin to fiddles and cellos. Cricket songs are performed by the scraping of their forewings. This is known as stridulation and is similar to a violin bow scraping and strings vibrating toward music. Crickets may be heard at any time of the day, but their chirping is most often heard at dusk and night. Their songs, delivered by males, serve much the same purpose as bird song: attract a mate and discourage rivals. The chirping rate depends on the species and is modulated by air temperature: the warmer the air, the faster the chirping. Entomologists have found this correlation to be very precise. Crickets hear these courtship songs with their tympana, similar to eardrums, located not on their heads but on their front legs.
Warm days and nights in August and September invite the penetrating songs of katydids. These relatives of crickets and grasshoppers produce a loud, shrill, metallic drone that often may go on longer than that famous 45-second piano chord of the Beatles’ “A Day in the Life.” I’ve found that local katydids, though loudly announcing their location, are easily overlooked. They are well camouflaged; most are leaf green and leaf-shaped. The male katydid’s courtship stridulation technique is less like a fiddle and more like scraping your fingernail over the teeth of a comb, but the result must sound like romantic music to the female.
Mammals at Night
A few mammals are audible in the late summer’s night. We hear coyotes every night howling and barking to bind their family pack. A quiet evening stroll may reveal the squeaks and rustling grasses and leaves as shrews stalk their tiny prey. Unique to this season, though, porcupines are stirred to romance. The males grunt and hoot, but it is a loud shriek by the female that the male porcupines and you might hear - her invitation to mating.
Birds into the Night
Into the evenings and nights of late summer, Barred Owls, whose young have fledged, hold the family together with distinctive hoots and raucous calls. This season’s message is not courtship; it is a contact message, “Here I am; where are you?” These owls are heard on the margins of deep woods, wetlands, farm fields, and roads, where they may find prey enough to share with the family.
Few other birds are heard at night late in the summer. Those studious Hermit Thrushes will practice their song right into the dusk and moonlight. Black-billed Cuckoos, though not common here, you may hear in the evening repeating their “cu-cu-cu” as they gorge on Fall Web Worms and Gypsy Moth caterpillars. And, of course, on the first crisp days and nights in September, Canada Geese, passing over in their efficient vees, give the season its most iconic voice.
Hearing them all is as good as seeing them!