The behaviour of mature male sperm whales on the Galápagos Islands breeding grounds

• Published in: Canadian Journal of Zoology
• Main Author: Whitehead, Hal
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1993
• Subjects: Physeter macrocephalus
• Online Access: http://dx.doi.org/10.1139/z93-093; http://www.nrcresearchpress.com/doi/pdf/10.1139/z93-093

The behaviour of mature male sperm whales (Physeter macrocephalus) was observed off the Galápagos Islands between 1985 and 1991. The abundance of males peaked in April and May at 3% of the population. Only 1 of the 18 photographically identified males was sighted off the Galápagos in two different years. In their residency periods off the Galápagos and their lack of preferred ranges, and in many aspects of their behaviour, males were similar to females. However, unlike females, males were sometimes seen alone and never performed any aerial behaviour. Although they were occasionally seen or heard together, there are indications that males avoided one another, perhaps by listening for the "slow click" vocalizations made by males approximately 75% of the time. One incidence of possible aggression between males was observed, and many males possessed parallel scars on their heads, presumably made during aggressive encounters. Males moved between groups of females, spending very approximately 8 h with each group. Groups of females were often revisited by particular males over periods of a few days but never over more than 1 week. Males showed no obvious preference for particular groups, although a few close associations between individual males and individual females were noticed over intervals of a few days. When males were present, females showed increased rates of making spyhops and sideflukes (indicating manoeuvring) and codas (a communicative vocalization). Copulation was not observed. The evidence is consistent with males' maximizing their expected reproductive success by roving between groups of females.