APPROACH TO THE ANALYSIS OF GRADED VOCALIZATIONS OF BIRDS

The purpose of this paper is to explore some techniques of representing and analyzing sound spectrograms, with reference to detecting and characterizing graded vocalizations. Description and classification of sounds based on their structure can be separate from research into their functions, and this paper considers affinities among calls as determined by their appearance as sound spectrograms only. Calls of two bird species Least Sandpiper, Calidris minutilla (Scolopacidae), and Patagonian Black Oystercatcher, Haematopus ater (Haematopodidae) are described by a simple method of hand digitization. A set of similarity measures among calls is derived for each sample of calls, based on the digitized representations, and multivariate analyses are performed on each of these sets. Structurally graded series seem to be represented clearly and accurately in graphical solutions from an ordination procedure (multidimensional scaling), coupled with results from hierarchical single-linkage clustering. The sandpiper calls form a simple system of adjacent grading; the oystercatcher calls show only a tendency toward grading of adjacent elements. © 1979 Academic Press, Inc.