# Sonograms

Sonograms are a handy way to visually "see" the sound of a bird's song. By carefully studying a sonogram, the speed of the singing, the spacing between notes, the pitch, and the complexity of the song all can be determined. In the following graphs, the left axis is measured in kilohertz (kHz). A hertz is a measurement of frequency - one hertz equals one cycle per second. For a comparison, most human speech is around 100 to 500 Hertz, or 0.1 to 0.5 kHz.

Compare these two sonograms of woodpeckers drumming, starting with the Downy:

Notice that the Downy is drumming about 15 times per second. Each mark is vertical, indicating a brief, staccato sound, like a drum. Now compare the speed of the Hairy Woodpecker:

Notice how much faster the Hairy Woodpecker drums, even though it is larger than the Downy. Though it is too fast to count the 30 taps per second of the Hairy Woodpecker when you are in the field, you can use the relative speed of each species to tell them apart.

Small mp3 audio files of each species depicted are located in the column to the right. After listening to each file, you may need to click your browser's Back button to return to this page.

Now compare these two whistled songs, first the clear notes of a Varied Thrush:

First, notice how the notes are horizontal, as opposed to the staccato vertical notes of the drumming woodpeckers. Each note lasts nearly a second in length, and does not rise or fall in pitch. Also, if you look closely, you can see fainter lines above each whistled note. These are called harmonics, and give the Varied Thrush's song its characteristic timbre.

Contrast this with the clear whistled phrases of the White-throated Sparrow,

Even though the notes are horizontal like the Thrush's, they are shorter in length, and grouped into phrases. Also, there are no noticeable harmonics above each note, so the timbre of the song is different; a clear rather than a buzzy whistle.

Finally, compare these two songs of warblers, starting with the Wilson's:

Notice how the notes are vertical, like the woodpecker drumming. However, they are much higher in pitch, ranging from four to ten kHz. This means that instead of a deep, drumming sound, they are sharp, high-pitched notes. Also, notice how the notes start out farther apart, then start bunching up around one second. When the Wilson's Warbler sings, you can hear this accelerating quality, which is diagnostic for the species.

Now compare the Orange-crowned Warbler:

Notice that though the notes are also vertical, they are much closer together than those of the Wilson's Warbler, how they are lower in pitch, and how the notes drop slightly in pitch at about 1.5 seconds. This is a trill, descending, then rising right at the end (though they don't always sing exactly like this).

I created all of the sonograms shown on this page using a free software called Raven Lite, offered by Cornell Labs. For more information, or to download the software for your own use, go to birds.cornell.edu/brp/Raven/

# Human Hearing

The range of normal human hearing allows us to hear most bird songs and calls. This makes sense in an evolutionary perspective, since being able to hear the calls of birds alerted early humans to both potential dangers and potential sources of food and water that they might not otherwise have found. The following graph shows the human hearing range for an individual with no hearing loss. This graph is different from the sonograms in that the frequency is now on the horizontal axis. Replacing its position on the vertical is volume in decibels (dB).

image from the Journal of American Association for Lab Animal Science

The black line that goes from left to right shows the volume required to detect a specific frequency of sound. Notice that we hear best between two and four kHz (the green zone), needing a very low volume in decibels to detect a sound. As frequencies get lower or higher, we need more volume in order to hear the sound. We can't hear any sounds below or above the 60 dB limit lines shown, unless the sound is very loud.

Compare the sonograms above with the 2-4 kHz best range for human hearing, and you can see that some of the songs, notably the Wilson's Warbler, are reaching the upper limit for hearing. Other species, such as the Golden-crowned Kinglet, are even higher in pitch, and are difficult for many people to hear.

Unfortunately, most people start losing the ability to hear sounds as they get older, especially higher-pitched sounds. Luckily, there are now devices that help to restore some of the lost hearing range. Normal hearing aids don't help, because they are designed for human speech recognition, so they boost the frequencies in the 2-4 kHz frequency range. To hear bird songs and calls above that range, a device is needed that either boosts them, or lowers their frequencies.

The SongFinder ™ is a device that allows the user to adjust the frequencies they can no longer hear down to a lower level that they can hear, while leaving lower frequencies intact. Reports from owners in the field have all been positive. They can hear the high-pitched songs and calls of Creepers, Kinglets, Warblers and others that they had been unable to hear. At the same time, the sounds of crackling leaves, wind, and human voices are not amplified, so they do not interfere with the bird songs.

To learn more about the SongFinder ™, visit their website at www.nselec.com

For others, illness or a genetic condition may affect their hearing. A cochlear implant may help to regain lost hearing in certain cases. An inspiring article about one woman who had severe hearing losss since she was a child, and her experience with getting an implant, is described in BirdWatcher's Digest, Volume 35, No. 6 (Jul-Aug 2013). Visit their website at www.birdwatchersdigest.com.

## Audio Credits:

1©2012, Gordon Beebe, Riverfront Park, CA
2©1992, Peterson Field Guide to Western Bird Songs

Great Egret

The little cares that fretted me, I lost them yes- terday.

Among the fields above the sea, Among the winds that play,

Among the lowing of the herds, The rustling of the trees,

Among the singing of the birds, The humming of the bees.

## Audio files

(after listening to each file, you may need to click your browser's Back button to return here)

Downy Woodpecker
[41 KB]1

Hairy Woodpecker [29 KB]2

Varied Thrush
[115 KB]2

White-throated Sparrow [57 KB]2

Wilson's Warbler
[29 KB]2

Orange-crowned Warbler [37 KB]2

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Website and photographs © 2016 by Gordon Beebe