Edinburgh Napier University

  The annual winter assembly of humpback whales (Megaptera novaeangliae) in tropical waters has been linked to reproductive activities, including birthing, calf-rearing, and mating. However, the sexual behaviour of this species remains largely undescribed and mating has never been witnessed. We examined 121 h of underwater videotaped footage of humpback whales obtained over five winter seasons in Hawaiian waters for evidence of penis extrusions by whales engaged in various activities in a range of social groups. In 630 different pods containing videotaped males, we noted 13 penis extrusion incidents. Penis extrusions were performed by lone singers (2 incidents), by the single escort to a mother/calf pair (6 incidents), and by principal and secondary escorts in competitive pods containing a female either with a calf (2 incidents) or without (3 incidents). All penis extrusions were brief (mean=44.0) s). Body length measurements (mean=11.53 m, SD=0.46 m, range=10.64 m to 12.05 m) were obtained using underwater videogrammetry on seven penis extruders, and suggested that the majority were sexually mature. Each penis extrusion in a competitive pod coincided with the penis extruder chasing another whale, and in four of five cases appeared to be directed toward another male. In the remaining case, the extruder appeared to attempt mating with a mother. Our findings suggest that penis extrusions in humpback whale competitive pods are often a concomitant of dominance contests between males.