The influences of body size and reproductive status on humpback whale (Megaptera novaeangliae) behavioral role, social interaction, and habitat use in Hawaiian waters
The Hawaiian Islands are the principal breeding grounds for North Pacific humpback whales. Pioneering field studies in the 1970s and 80s characterized much of their behavioral ecology. However, little attention was paid to the influences of body size or reproductive status. In other species, body size plays an important role in breeding success and thus may influence male-female associations. Larger females are often more fecund and/or better able to produce and rear higher-quality offspring than are smaller females, and larger males are often more successful than smaller males in securing females. Reproductive status may also influence male-female associations as well as habitat selection. Females without offspring often have a higher reproductive potential than those with offspring and thus may be favored by males. Also, because females without offspring may still attract some males prospecting for mating opportunities they often segregate themselves and their offspring in order to avoid male harassment. Dr. Adam Pack and his colleagues have been examining the influences of body size and reproductive status on humpback whale behavioral roles, social interactions and habitat use in Hawaiian waters. Using a unique underwater videogrammetric technique in conjunction with an extensive archival catalog of individual whale identification images, they have measured the body size of over 500 whales and examined their associations and habitat uses within and across breeding seasons. Findings have revealed which males during competitive interactions are most successful in securing the position closest to a female, whether female size is related to calf size and male attraction, whether male-female dyads reveal assortative pairing, which males “sing”, how male attraction is related to female reproductive status, and how females vary their habitat use as a function of their reproductive status as well as the age and size of their calf. Dr. Pack will present these findings and discuss his latest collaborative efforts to determine whether male song is an honest indicator of male fitness, and how suction cup acoustic tags can provide a deeper understanding of humpback whale habitat use.