Songs and courtship behavior of male humpback whales (megaptera novaeangliae) in the North Atlantic
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Abstract
During the breeding season, male humpback whales sing long, complex songs. The function of singing is unknown. As a display, however, it may be expected to convey something of the status or quality of the individual. Here I present a hypothesis for how singing might allow a listener to assess the physical condition of a singer.
This study took place on Silver Bank, Dominican Republic, the major breeding area for humpback whales in the North Atlantic. Silver Bank has areas with coral reef and areas of sandy bottom with few coral heads. There are fewer singers near the reef than in an area where coral heads are rare. However, there are relatively more singers near the reef in March than in February, although whale density peaks in February. This suggests that the value of singing in any location may change depending on temporal characteristics of the population.
Singing humpbacks make inordinately long dives. Some singers appear to be able to dive longer than others, and, thus, seem to be 1n better physical condition. I propose that the long dive times provide a means by which a singer's stamina could be assessed by another humpback.
Characteristics of the songs convey information about a whale's dive time. Most important is that the received signal gets fainter as the whale rises to the surface. This is an unfakable aspect of the display. In addition, song length correlates with dive time. Also, aberrations in the song pattern were associated with breathing in my sample. Therefore, by singing, a male humpback is broadcasting information about his dive times.
I hypothesize that dive time and song duration are factors in the competition between singers, specifically that longer dives and songs are better displays. In support of this theory, I find that songs and dive times are longer where singing competition seems to be greater. Also, singers with longer songs or dive times appear to be more persistent than are singers with shorter songs or dive times.
Singers of aberrant songs are found 1n areas where there are few other singers, and, therefore, appear to be less competitive. Aberrant songs are shorter than normal ones. If aberrant singers are peripheral males, this would support the theory that song length is a factor in song competition.
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Dissertation (Ph.D.)--Boston University
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