FREQUENT HUMPBACK WHALE SONGS RECORDED IN GLACIER BAY , ALASKA IN FALL 2000 and 2001

Abstract

Humpback whale songs have rarely been recorded in Alaska waters. High-latitude humpback whale songs that occur outside the presumed winter mating season are interesting because song is thought to be a male mating-related display. Using a bottom-mounted hydrophone and computerized monitoring system in Glacier Bay, southeastern Alaska (58 25' N, 135 55' W) we recorded 25 hours of humpback whale song on 29 different days between August and November in both 2000 and 2001. We compared the best Alaska recordings with songs recorded off the whales' winter range in the Hawaiian Islands in winter 2000 and 2001, and measured their degree of similarity on a variety of acoustic parameters. Individual song units were extracted from the recordings, and computer program 'Acoustat' quantitatively measured 97 attributes of each unit's frequency, temporal and contour characteristics. The dimensionality of the measurements was reduced with a principal components analysis to determine which measurements accounted for the most song unit variance. The first 18 principal components, accounting for 80% of the variance of the original measurements, were classified with a discriminant analysis by year and region. We found significant differences between units by region and year, but also found that the model could correctly classify units into the proper region and year. Most song sessions were less than one hour long, although a few sessions of up to 270 minutes were observed. The absence of song prior to August suggests that song is quite rare in mid-summer, whereas song absence later than November probably resulted from whale movement out of the study area. We surmise that we recorded many more humpback whale songs than previous Alaska studies (e.g. McSweeney et al. 1989) because remote monitoring allowed us greater acoustic monitoring effort in the fall regardless of limited daylight and inclement weather. We speculate that the incease in song in late summer and fall may correspond with the beginning of seasonal hormonal activity in male humpbacks prior to the migration to the winter grounds.