Sea lions recognize the local competition

Australian sea lions (Neophoca cinerea) are among the rarest members of the family Otariidae. They form breeding colonies on the beaches of Australian where males aggressively defend females with a series of short barks. In an unusual twist, Australian sea lions have a breeding cycle lasting over 17 months with little synchrony between colonies. Even colonies on adjacent beaches may have a breeding cycle offset by up to 8 months.

Recent studies demonstrate that each Australian sea lion gives a unique bark (Gwilliam et al. 2008). The questions is, do males recognize and respond differently to the barks of local males versus the barks of foreign males from more distant colonies. To answer this question, Marie Attard and her colleagues conducted a play-back experiment at two colonies separated by 180 kilometers in Southern Australia (Attard, et al. 2010). The researchers played a series of 10 barks from either foreign or local males to series of males who were actively guarding females and recorded the behavior of the guarding males. The results indicated that males responded more quickly and more aggressively to barks from local males.


Figure 1. Australian sea lions on the beach at one colony site. (Photo by Sheilaellen)

Attard and colleagues study is the first to show geographic variation in sea lion calls and that sea lions can discriminate between barks produced by local versus foreign males. These results seem appear counter to the “dear enemy hypothesis” which proposes that aggression toward neighbors should be lower than that shown
toward strangers. In this case, it appears that local males present a greater threat due to increased local competition for access to females in the colony. By recognizing the barks of local males, mate-guarding males focus their time and energy on those males that pose the greatest potential threat.

References

Attard, M.R.G., Pitcher, B.J., Charrier, I., Ahonen, H., and R.G. Harcourt. 2010. Vocal discrimination in mate guarding male Australian sea lions: familiarity breeds contempt.
Ethology, 116:704-712.

Gwilliam, J., Charrier, I., and R.G. Harcourt. 2008. Vocal identity and species recognition in male Australian sea lions,
Neophoca cinerea. Journal of Experimental Biology, 211:2288-2295.


Photo credit: Sheila Ellen Thomson