Jr. Clemmons, THE STRUCTURAL SIGNIFICANCE OF A VOCALIZATION THAT STIMULATES GAPING IN BLACK-CAPPED CHICKADEES, Behavioral ecology and sociobiology, 40(4), 1997, pp. 243-251
In a variety of avian species, vocalizations used to stimulate gaping
in nestlings during feeding share similar features such as broad frequ
ency range, multiple spectral components, and sudden onset. It is curr
ently not understood what functional significance, if any, these acous
tic features have for close-range communication. One example of such a
vocalization is the ''squawk'' of the black-capped chickadees (Parus
atricapillus). The present study analyzes the significant features of
the squawk by observing the response of chickadee nestlings to field p
laybacks of natural and computer-modified squawks. Of the features tes
ted, frequency range appears most critical, but responses to frequency
ranges change with age, such that low frequencies are most stimulatin
g around the time of hatching but cease to elicit gaping after 5 days
posthatch. Aperiodic stimuli and computer-modified squawks with gradua
l onsets tend to be less stimulating than natural squawks at some ages
, but these differences are not significant at any age. The functional
significance of the broad frequency range of the squawk is discussed,
including the possible role of accommodating shifting frequency prefe
rences related to ontogenetic changes in auditory sensitivity and elab
oration of the vocal repertoire.