Female Humpback Whale (Megaptera Novaeangliae) Reproductive Class and Male-Female Interactions During the Breeding Season

Meagan E. Jones (2010)

This study examined whether female reproductive class (i.e., presence or absence of a calf) in humpback whales (Megaptera novaeangliae) affects female behavior and male-female interactions on the Hawaiian breeding grounds. From 2003-2008, 295 female-calf groups (with or without a male escort) and 256 female no-calf groups (with a male) were observed. Forty-one female no-calf groups were confirmed male-female pairs by genetic sexing or photo-identification. Focal follows of 36 male-female pairs and 50 female-calf groups (29 escorted and 21 unescorted female-calf groups) were analyzed for time budget and movement estimates. Relative fluke size (fluke photogrammetry, n=30) and sighting histories (n=9) were used to estimate age-class for 39 individuals within focal follows. Escorted female-calf groups spent significantly more time traveling and less time resting than male-female pairs and unescorted female-calf groups. Indeed unescorted female-calf groups had time budgets more similar to male-female pairs than female-calf groups with a male. Male behavior and relative body size also affected female behavior and movement patterns: lone males chased females with calves significantly more than females without calves. Fluke sizes of mothers who were chased were significantly smaller than mothers not chased, and the chasing males tended to have smaller flukes (i.e., younger age-class) than males that did not chase. I also conducted 34 playback experiments (broadcasting sounds of competitive males) with 14 female nocalf groups (male-female pairs) and 20 female-calf groups (11 escorted and 9 unescorted female-calf groups). Results of playback trials indicated that females with calves were significantly more likely to avoid playbacks of sounds produced by adult males than females without calves. Overall, the range and variability of female behavior and movement patterns, especially around males, was striking. Results indicate that female reproductive class is a key factor in determining how females respond and interact with males during the breeding season, but also suggest that male-female interactions during the breeding season are a reflection of a combination of factors, beginning with female reproductive class, but also including costs and benefits of specific male escorts, stage of the reproductive cycle, relative body size and/or age-class.

Read Full Text