Application of dynamic programming matching to classification of budgerigar contact calls

Dynamic programming (DP) matching was applied to classification of budgerigar contact calls. Our DP-matching algorithm calculates distances between two calls with time warping. It was compared to other methods including linear matching methods and methods using cross correlation, and was evaluated in classifying calls into natural groups. The DP-matching method with two peak frequencies with some tolerance in frequency comparison (DP2peak) and the cross-correlation method using two peak frequency tracks with frequency shift (Corr2shift) were equally effective in classifying obviously different calls. DP2peak proved more effective than any other methods tested in classifying minutely different cagemate calls. Use of two peak frequencies, time warping in matching calls, and tolerance of frequency shift were found to be the three most important factors in mimicking the bird's own classification of natural calls, whereas intensity differences of peak frequencies did not play an important role. The possibility of similar processes of call discrimination in the bird's brain, such as simultaneous perception of two frequencies and time warping in comparing calls, was discussed in relation to these results.