The music of nature

Nature offers us some wonderful summer entertainment, an orchestra of birds, frogs and insects with their own musical melodies. In late April and certainly by mid-May, migrant birds in the Southern Appalachian mountains have begun to bridge the musical void that began last summer. Robins and other thrushes, eastern bluebirds, song sparrows, and especially warblers appear, and as daylight hours increase, these birds develop a need to express themselves in song.  

The male of each species is the one who most commonly announces his presence, although some females do call. The female cardinal actually produces a song. Generally, male birds are the songsters, and the function of their songs has not always been appreciated, much less understood. We now know, however, that male birds must sing. Their hormones require singing, and the songs are directly influenced by the day’s length.

The effects of daylight hours on birds have only been studied for  a few decades. As Appalachian migratory  birds travel northward in the spring, they are exposed to increased daylight. As this occurs their sexual organs vastly increase in size, along with a tremendous surge in the hormones that are related to mating. A side effect of these changes  is to stimulate singing behavior.

Wood thrushes, for example, spend their winters in Central and South America. They pass through the Southern Appalachian Mountains silently every autumn but appear again in early May. At home in our cove,  we have kept records of the birds as they reappear each spring. It is almost always on the first of May that we begin to hear the reed-like voice of the male wood thrush.

Song serves a number of purposes for these spring friends. First, it announces, “I am here.”  This announcement is for other members of its species and especially for other males and females. For other males, it signifies, “I own this property.” For females it signifies, “I am available!” It is a territorial and mating availability announcement.

Once a male bird has achieved its purpose through song— attracting a mate— it continues to sing for awhile, probably to keep other males of its species away. However, the singing diminishes as the nesting season advances, and by the time his young have fledged the nest, the male has become a silent partner.

Frogs and Toads

Although amphibians, frogs and toads exhibit a similar purpose through singing in the spring, their singing periods, occurring for only a week or two, are much shorter than birds. But can they sing!

Consider, for example, the spring peeper, Hyla crucifer. Less than two-inches long, this frog is the one in this region with an “X” on its back. As a soloist it is not very impressive, with only a high, piping whistle repeated every second. However, a chorus of peepers is an entirely different matter. When in harmony, peepers sound like sleigh bells.

All of the area’s frogs and toads have a voice. The common American toad, Bufo americanus, can be identified by its trilling notes, which last from 6 to 30 seconds each. The notes are repeated at 30 to 40 per second intervals. Each toad species, however, has its own trilling sequence and volume.

The following chart summarizes the calls of some common Southern Appalachian mountain frogs and toads.

Insect Songsters

The most notable mountain songsters that fill the days and nights with singing are in full voice in the autumn, and they are mostly common insects: cicadas, katydids, crickets and grasshoppers.

Cicadas are of two types, those that appear annually (periodical cicadas) and those that appear every 17 years. Both types sing, mainly during daylight hours, with the 17-year species singing mostly in the morning and the periodical species in the afternoon. None sings at night.  On the other hand, crickets and katydids sing during the night and most grasshoppers, like cicadas, are diurnal (daytime) songsters.

Since all insects are cold-blooded, those that sing do so in relation to the air temperature—  faster in warm environments, slower when the temperature drops. Most songs end when the temperature is below 55° Fahrenheit.

Insect songs are species-specific; that is, members of their own species immediately recognize their songs, but they may not be recognized by other species. Generally, only the males produce the songs (referred to as “calling songs”).

Only a few insect families have members that can sing. The cicada belongs to a different insect order and is not related to any of the other singing insects. All other “singing” insects belong to a single order (called the Orthoptera). This includes  grasshoppers, crickets, and katydids.

The songs of crickets and katydids differ in that the songs of crickets are musical to our ears, whereas katydid songs are mostly a series of buzzes, with a longer duration and higher pitch. Some biologists have suggested that in addition to attracting individual mates, males in some singing species come together in large groups so that females far away may hear their collective voices.

Whatever the purpose, it is well known that most insect music is produced by “stridulation,” or rubbing two body parts together. Among the crickets and katydids, these sounds are produced in the base of the forewings. Several species of grasshoppers produce their music by rubbing their hind legs against their front wings. Male cicadas have sound-producing organs on the sides of their abdomens, which are activated by contracting abdominal muscles to produce sounds.

Some insects’ songs are directly related to air temperature. This is particularly true with crickets. In fact, it is possible to correlate the temperature of the air and the song sequence of crickets in the following way:  Count the number of chirps within 13 seconds and add 40. The resulting number will be very close to the Fahrenheit air temperature.

Even though scientists have studied animal voices for several centuries, we still do not know everything about nature’s music. Perhaps you will perceive a new truth about this fascinating phenomenon by carefully listening to nature’s mountain music.