A Bird’s Tale

Will Your Acoustic Index Detect Spring This Year?

Tue, 03/16/2021 - 10:00am

The sounds of spring. What are they for you? For us, there are many. Even the first whistled “hey-sweetie” songs of black-capped chickadees, which may begin in January, are a reminder that spring is on the way. Soon after, we began hearing the rough, warbling songs of house finches and the first halting trills and twitters of the neighborhood song sparrows. Tufted titmice have been loudly proclaiming “peter, peter, peter” across the landscape, too, and a male northern cardinal belts out his “teer-teer-teer” from just outside our bedroom window at dawn.

Now that we are well into March, we have since added the first low, buzzy “peents” followed by the high twittering sounds of displaying male American woodcock in the evenings. That is certainly a sound of spring for us.

Soon we will be hearing the caroling of American robins echoing in every city and town in the state. By April the loud evening choruses of spring peepers will be a welcome sign of spring to many.

By the time May rolls around, the volume of bird sounds at dawn and frog sounds in the evening will be amazing and complex, with dozens of species in any one spot. Some single locations will have hundreds of individual vocalizing birds and frogs. When we reach the warmer month of June, the high-pitched sounds of insects will be part of the soundscape.

We have written before about the use of automated sound recording devices to study birds. As you can imagine, researchers using such devices can capture thousands of hours of recordings of the sounds in any environment. And while it is possible to have bird sound identification experts review some sample of those recordings to identify the species present, the sheer volume of sound recordings tends to outpace that capacity. Researchers are increasingly developing automated detectors that can find and identify the sounds (or at least some of the sounds) of some species. But even these automated computer algorithms are not foolproof and require an expert to review the identifications and correct any mistakes.

But there is another avenue for using sound recordings to understand more about the environment and its biodiversity that skips over the need to identify individual species. Imagine contrasting the total soundscape of birds and the environment around your home in January with the soundscape in May. Without even knowing what any of the birds were, you would recognize that the natural sounds from birds and other creatures was louder in May than it was in January. Scientists have developed what are called acoustic indices to quantify those differences in the total soundscape made up of all the sounds recorded at a given location.

Some of these acoustic indices measure the total volume of sound. Others may measure the energy in different frequency bands—very high for insects and bats; in between for songbirds and frogs, and low for birds like owls. Some acoustic indices may measure the variability of the total sound over time or among locations or among different habitats. Acoustic indices can be used to study how climate change may be impacting when the peak of song activity is in general or for certain frequencies. It is possible to develop indices of human-caused noises, like cars and other industrial noises, and to contrast those with indices of natural sounds to study impacts to birds and other sound-producing creatures due to various human activities.

Even without sophisticated sound recording units and computers, we humans have our own built-in acoustic indices that tell us when the seasons change. We will enjoy the soundscape of spring with our own ears as it unfolds around us day by day. We hope you will, too.

[Listen to a soundscape from a June morning at the Ocean Point Preserve here.]

Jeffrey V. Wells, Ph.D., is a Fellow of the Cornell Lab of Ornithology and Vice President of Boreal Conservation for National Audubon. 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 books, “Maine’s Favorite Birds” (Tilbury House) and “Birds of Aruba, Bonaire, and Curaçao: A Site and Field Guide,” (Cornell University Press).