304 Main Street 
Etna, New York 
September 16, 1964 
Dr. Martin Moynihan 
Canal Zone Biological Area 
Drawer C 
Balboa, Panama Canal Zone 
Dear Martin: 
By now you should have received the spectrograms of Callicebus . If 
not, they should reach you shortly. I mailed the recorded tape strips on 
the 11th. 
The "grunt" appeared to resolve fairly well. I was interested in 
the human-like resonance bars. The resonance was audible on half-speed 
playback as a rising then lowering pitch. The fundamental frequency 
remained constant at about 220 cycles per second-calculated from the num- 
ber of vertical beat lines per second. 
The "sneeze" was as expected, an abrupt sound covering the whole 
range of frequencies under analysis as white noise. You can see the rela- 
tive time the various frequencies reached the microphone as a slanted line 
on the spectrogram. 
The project on avian vocalizations which I discussed with you this 
summer has been approved by my committee (C. G. Sibley, Bruce Wallace, 
LaMont Cole). Therefore, I would like to outline it, as you requested, as 
a possible proposal for a Smithsonian Fellowship. // Basically, I would be 
studying the ecology of avian vocalizations, i.e., the forces of the 
physical and biological environments selecting for or against certain 
sound characteristics. 
Factors of the physical environment such as vegatation density, 
temperature and humidity and topography control the carrying qualities of 
sound. Generally, there is a certain range of frequencies within which 
optimum sound propagation is attained for each habitat. Data for certain 
avian sounds indicate a correlation between frequency and form of vocali- 
zation and optimum sound propagation for a particular physical environment. 
In a general way, this habitat-sound correlation has been mentioned in 
many scientific and popular articles. However, no data has been obtained 
pertaining to possible selective factors for sound characteristics. 
The biological aspects of avian sounds have been studied, but never 
in relation to the physical environment. It is my hypothesis that in a 
particular environment, certain sounds are selected for due to the physical 
limitations of the environment. Then, within the parameter of the physical 
limitations, the biological parameters of anatomy and inter-and intraspecific 
competition, etc., operate to mold the species-specific vocalizations. 
