Agnostic Behavior in Wild Male Magellanic Penguins: When & how do they interact?

As discussed in lecture, game theory predicts that individuals display aggressive behaviors relative to the potential costs of winning. Therefore, they should act more aggressively when the potential benefits of winning are high and less aggressively when the benefits of winning are low. Male Magellanic penguins compete for nests prior to and post egg-laying. Nests available pre egg-laying can be used immediately for breeding and have a greater potential value than failed nests available post egg-laying. They still compete for failed nests to stake ownership for the next breeding season. Nests with greater cover (deeper burrows with smaller entrances) should be more valuable than nests that have less cover (shallow) because they provide extra protection for offspring. This study aimed to see if male Magellanic penguins have rules of engagement during the breeding season and if they follow game theory predictions for aggressive behaviors.

Competition between penguins over nests involves bill dueling and fighting. Bill dueling is less aggressive because it holds less risk of damage. Fighting is more aggressive because it causes physical harm (bill cuts and flipper hits) to one or both penguins. Researchers hypothesized that male penguins should be more aggressive during the early season (pre egg-laying) when the potential value of nests is higher and that this level of aggressiveness would depend on the degree to which the nest was covered.

Competition between males was recorded for four breeding seasons. Relative frequency of bill duels and fights and severity of fights (based on number of flipper hits, length of cuts and duration of fight) was measured. Since almost no male competition occurred while females incubated eggs, they deemed competition before October 21 as pre egg-laying and after as post egg-laying.

Results showed that fighting rates were greater before egg-laying, while bill dueling rates were greater post egg-laying. Fight duration and length of cuts was shorter before egg-laying than after egg-laying, but the number of flipper hits was not significantly different. As the degree of nest cover increased, fight duration and length of cuts increased. Nests over which penguins fought had greater cover than those over which they bill dueled. In addition, 96% of fights occurred inside nests while 87% of bill duels occurred outside of the nests.

Based on these results, they concluded that fighting was more common before egg-laying when nests had the highest potential value for reproductive success while bill dueling was more common over the less-valuable failed nests. They reasoned that fights pre egg-laying were shorter in duration because opponents varied in size and strength, thus a loser was determined more quickly. The duration and damage that occurred during fights was higher over covered nests because these nests provided more protection for offspring and thus held greater reproductive value. They reasoned that bill duels after egg-laying were between penguins of similar sizes (reproductively unsuccessful penguins) and served to test both willingness and fight strength of one another. In conclusion, these males generally behaved as game-theory predicted by acting more aggressively over nests with higher reproductive potential and value.

Renison, D., Boersma, P., Van Buren, A.N., & Martella, M.B. (2006) Agnostic behavior in wild male Magellanic penguins: when and how do they interact? J Ethol, 24, 189-193