Abstract
Fin whale (Balaenoptera physalus) song consists of down-swept pulses arranged into stereotypic sequences that can be characterized according to the interval between successive pulses. As in blue (B. musculus) and humpback whales (Megaptera novaeangliae), these song sequences may be geographically distinct and may correlate with population boundaries in some regions. We measured inter-pulse intervals of fin whale songs within year-round acoustic datasets collected between 2000 and 2006 in three regions of the eastern North Pacific: Southern California, the Bering Sea, and Hawaii. A distinctive song type that was recorded in all three regions is characterized by singlet and doublet inter-pulse intervals that increase seasonally, then annually reset to the same shorter intervals at the beginning of each season. This song type was recorded in the Bering Sea and off Southern California from September through May and off Hawaii from December through April, with the song interval generally synchronized across all monitoring locations. The broad geographic and seasonal occurrence of this particular fin whale song type may represent a single population broadly distributed throughout the eastern Pacific with no clear seasonal migratory pattern. Previous studies attempting to infer population structure of fin whales in the North Pacific using synchronous individual song samples have been unsuccessful, likely because they did not account for the seasonal lengthening in song intervals observed here.
Highlights
Song can be described as a regular and repeated sequence of sounds, organized into a hierarchical structure [1], song complexity varies across taxa
Fin whale song recorded in the Gulf of California was consistent across a longer observation period [9] and was consistent with the song inter-pulse interval (IPI) of a previously recognized resident population of fin whales [11]. These results suggest a better understanding of the seasonal patterns in the IPI of fin whale song is necessary before their use for population differentiation can be fully evaluated in the Pacific
When we found substantial variability around the median IPIs in some months, we further assessed the data to determine whether this variability could be attributed to plasticity in IPIs of the same song type or if the variability could represent occurrence of more than one song type
Summary
Song can be described as a regular and repeated sequence of sounds, organized into a hierarchical structure [1], song complexity varies across taxa. Seasonal changes in song have been well studied in birds [2], and are known to occur in baleen whales [3]. Humpback whale (Megaptera novaeangliae) songs evolve during the breeding season, and change from one year to the with neighboring populations sharing some song components [4, 5]. Not consistently referred to as song, the repeated regularly timed pulses that make up song have been documented from fin whales (B. physalus) in all ocean basins [8,9,10,11] and where populations have been monitored for extended periods, song structure has been relatively stable over time [9,10,11]. The prevalence and nature of seasonal change in fin whale song in other ocean basins has not been examined
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