Song Variation in Prothonotary Warblers

I never expected to contribute to the conservation of birds, except by participation in The Birdhouse Network, Feederwatch, or a CBC/NAMC census, and of course by donating money. So it’s amazing that this is the third year I’ve been working on a project investigating song variation among Prothonotary Warblers with adjoining territories along a nest box trial along the cedar streams of the New Jersey Pinelands. 

INTRODUCTION
The project addresses several questions with regard to Prothonotary Warblers: Can an individual male be distinguished from another male by voice characteristics visualized in an audio spectrogram (the technical term for ‘sonogram’)? Will individual voice characteristics be retained from year to year? If an individual retains a distinct identifiable voice, this project could provide a non-invasive, reliable census tool for researchers and land managers. If, on the other hand, voice characteristics of adjoining males are indistinguishable, or become similar over time, then how/why did birds from different natal environments adapt their songs to each other? . . . by borrowing syllables from neighbors? These are difficult questions for an amateur bird lover to tackle, but with hard work and some luck our data may answer these questions.

For years I watched W. John Smith, Jr., a professor of  biology at Penn, and his wife Anne Marie, standing quietly by a wooded stream, holding a large plastic parabola in the air, with packs and mysterious gadgets hung over their shoulders and about their waists. I didn’t know why they were recording, but when John asked if I wanted to help with his project, I didn’t have to think twice. After three field seasons helping him, I thought I might be able to do a similar project. After George Reynard, a master recordist, gave me my first microphone, I was hooked.

METHODOLOGY
The methodology for gathering data is straightforward. Find accessible habitat where a number of the same species breed from year to year. Band as many males of the species as possible with USFWS and color bands. Record the songs of color-identified birds, produce audio spectrograms from the audio tapes, and compare them. Find the color banded birds in the next breeding season, record their songs again, and compare. Analyze the data and draw conclusions.

Working on John Smith’s spectrograph machine in his acoustical lab at Penn showed me there was huge variation in the visual complexity of songs of different species. If a species’ song were “supercallafragalisticexpealedotious”, the number of variable components would far exceed my ability. I needed a species with simple, discreet, song components like “sweet, sweet, sweet,” which had not been studied, and was accessible in numbers on land that would not be developed. In 1997 I began helping my friend, Augie Sexauer monitor a Prothonotary warbler nest box trail at Hawkins Road in the Red Lion Bear Swamp Preserve, Medford Lakes, NJ. There I saw several species that were ideal for a study and the land had recently been protected. Prothonotary were numerous due to the allure of the nest boxes and their song was a simple repetition of a single note. It looked very promising and Don Jones a fellow member of the Delaware Valley Ornithological Club began working with me.

I applied to the Bird Banding Laboratory for a sequence of colors. I band the right leg with a USFWS aluminum band and the left leg with two colored plastic bands, each 1/8" high. We call our birds by their leg colors: Red/Red, Blue/Yellow, and so on.

During 1999 the birds we recorded were unbanded, but we think some have returned, from a comparison of their sonograms. The 2000 season was rainy and windy creating leaf rustle that garbles a sonogram, and a student pilot buzzed the area constantly. By the time I got some “color” on a few males, the nesting season was over and the birds were off territory. I despaired, because in two seasons there had been a lot of 3:30 a.m. wake ups, long drives and bridge tolls with not too much to show. Fast forward to April 23, 2001 and Don’s email saying that “Red/Red and Yellow /Yellow (banded June of 2000) have returned!!.” We were ecstatic.

Most birders are aware that there’s a sub-group of diehard birders who also record bird songs. The recording tradition began in1889 when Ludwig Kock made the first recording of a caged bird in Germany. Sylvester Judd played a recording of his pet Brown Thrasher at an AOU meeting in1898. By1932, with improvements in technology, Cornell University ornithologists were collecting bird songs and using them to teach. Today miniaturization and digitization have increased the reliability of portable devices to an unbelievable degree. Every PC can produce sonograms using software available from Cornell Library of Natural Sounds and shareware free on the Internet. Don Jones purchased “Canary” (Macintosh only) from Cornell’s Laboratory of Natural Sounds. I use “Syrinx”, a free download also from CLNS. Don spent many days reviewing the audio tapes, producing sonograms, and creating a filing system for the data. We will be able to examine individual males, locations, note types, etc., to determine what patterns are emerging.

CONCLUSIONS
The full range of avian song is not available to our ears. The avian voice box, or syrinx, has two chambers which enable a bird to duet with itself, producing different tones at the same time, but there are no vocal chords. Volume is controlled by air sacs which inflate to put pressure on the muscles of the syrinx making sounds higher, louder, more tonal, etc. A sonogram is a graph of the sound we hear and the sounds we don’t hear or can’t distinguish. Pitch shows on one axis and time on the other. The wavy line of the graph shows volume, harmonic overtones, and subtle nuances generated by the syrinx. It displays for the human eye what a bird hears.

The 2001 season was our best, with eight new males banded and many more birds recorded. Although, we have no recordings for a few banded birds, which means that even if they return, and we locate them, we won’t be able to say whether they changed or not, we’ve doubled our chances for the coming field season. If 50% survive migration, as in 2000, we’ll have at least four birds to work with. Don, Augie, and I spent many happy days tending the Golden Swamp warblers of Hawkins Road and recording their songs and we look forward to the next brood and the thrill it is to help them on their way.

If you have a study or project that you conducted on behalf of cavity-nesting birds, please share it with us. All text must be submitted in electronic format. Images can be submitted in either electronic or paper format.
Click here for submission requirements and criteria.

NestWatch
159 Sapsucker Woods Ithaca, NY 14850
You can also e-mail your photo as an attachment to:
nestwatch-support@cornell.edu
Thank you in advance for your contribution. 

Please note, all submissions become the property of the Cornell Lab of Ornithology.