One of the most impressive sights in the Antarctic are the huge colonies of penguins, especially king penguins. The huge mass of bodies and pointy beaks seem to simply scare off enemies. Various hypotheses have been proposed as to why the animals exhibit this behavior. A French-Swiss research group has investigated four hypotheses and discovered that a large density is much more advantageous, despite stress with neighbors.
Do more eyes see aggressors earlier and allow for appropriate (escape) responses, or does the sheer mass of individuals reduce the likelihood of an attack on a single animal, or is it the attempt to protect oneself from attack in the midst of groups that encourages group formation? And how much does aggression toward neighbors weigh on potential benefits of group living when they are too close? All these questions have been investigated by a research team from the University of Strasbourg with the participation of the Swiss Ornithological Institute Sempach.
The results show that at high densities, attackers are detected earlier and allow appropriate protective responses, while at lower densities king penguins are more preoccupied with aggressive behavior against neighbors and are thus distracted from attackers. More protection by standing in the middle or by reducing the risk due to the crowd could not be confirmed by the team. This study appeared recently in the journal Behavioral Processes.
In their work, the team led by behavioral scientist Professor Vincent Viblanc and his then doctoral student Tracey Hammer investigated the four hypotheses of “many eyes,” “dilution effect,” “selfish herd,” and “distracted prey,” all of which seek to explain colony formation in animals. In order to do this, they explicitly approached breeding king penguins on the French subantarctic island of Crozet at different times according to a standardized protocol and noted the time of a reaction and the distance to the approaching individual. They also noted reactions of the animals towards the birds’ neighbors. Furthermore, they examined the density of the groups and were thus able to link the behavior of the individual animals with the group density.
Basically, when a potential danger appears, either a threatening gesture towards the source of danger or the start of a flight behavior is expected. The team’s results showed that penguins living in a less dense colony at the beginning of the breeding season reacted later and later to approach when the immediate neighborhood became denser, but at the same time became more aggressive toward neighbors. Flight behavior was also reduced, the team writes. As the colony densifies over time due to immigration, and individuals only then start breeding, they become more alert to approaching potential sources of danger, triggering a protective response. This includes, above all, increased attention and possible flight or defense behavior.
In contrast, the team did not detect any change in the distance at which flight is initiated. This is all the more surprising because the hypotheses so far assumed that animals on the periphery of a group or colony would react earlier to an attacker by fleeing. According to the team, one possible explanation for the phenomenon is the high cost of the reproductive strategy. King penguins reproduce only every two to three years, depending on their success, and raise only one chick. Since this involves a high personal energy investment, king penguins tend to rely on early detection and defense. “FID (flight initiation distance, editor’s note) may then be a relatively inflexible trait in breeding individuals of this species and therefore dilution or distraction effects on this trait may be small,” the research team writes.
Overall, the team concludes that “prey behavioral decisions regarding approaching threats are complex and likely explained by a mixture of mutually non-exclusive hypotheses.” This seems to provide at least a step toward explaining the huge colonies of king penguins despite the proximity to unpreferred neighbours.
Dr Michael Wenger, PolarJournal
Link to study: Hammer et al (2023) Behav Processes 210 Disentangling the “many-eyes”, “dilution effect”, “selfish herd”, and “distracted prey” hypotheses in shaping alert and flight initiation distance in a colonial seabird; doi.org/10.1016/j.beproc.2023.104919
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