Two-component calls in short-finned pilot whales (Globicephala macrorhynchus)

Short-finned pilot whales (Globicephala macrorhynchus) have complex vocal repertoires that include calls with two time-frequency contours known as two-component calls. We attached digital acoustic recording tags (DTAGs) to 23 short-finned pilot whales off Cape Hatteras, North Carolina, and assessed the similarity of two-component calls within and among tags. Two-component calls made up <3% of the total number of calls on 19 of the 23 tag records. For the remaining four tags, two-component calls comprised 9%, 23%, 24%, and 57% of the total calls recorded. Measurements of six acoustic parameters for both the low and high frequency components of all two-component calls from the five tags were compared using a generalized linear model. There were significant differences in the acoustic parameters of two-component calls between tags, verifying that acoustic parameters were more similar for two-component calls recorded on the same tag than for calls between tags. Spectrograms of all two-component calls from the five tags were visually graded and independently categorized by five observers. A test of inter-rater reliability showed substantial agreement, suggesting that each tag contained a predominant two-component call type that was not shared across tags.