Viblanc VA, Valette V, Kauffmann M, Malosse N, Groscolas R. 2012. Coping with social stress: heart rate responses to agonistic interactions in king penguins. Behavioral Ecology 23(6):1178-1185.
Most animals live solitary lives, interacting with their own kind only to mate, raise young, or fight. In contrast are group-living animals, from meerkats to humans to Greylag Geese. Their sociality means an easier time locating mates and spotting predators, but it can also mean more disease and competition for resources. This competition can lead to injury and stress.
Breeding King Penguins crowd onto shores in huge numbers and claim tiny territories – about one-half of a square meter – where they incubate their egg and then brood the resulting chick. They have to defend these territories constantly, on average 100 times per hour. This occurs over a tiny space, since the penguins have an egg or chick on their feet and so can’t move much; most aggressive interactions are with neighbors no more than 50 cm away. Stressful interactions may not sound like a big deal – hey, we’re all stressed, right? – but these penguins are trying to maintain a high body temperature in cold conditions and keep their baby warm, and while doing that, they fast for weeks. They do not have energy to waste on stress.
Viblanc et al. monitored the heart rates of 20 King Penguins in a subcolony consisting of 3500-4000 breeding pairs. (Yes, subcolony. The entire colony was about 23,000 breeding pairs.) They observed the interactions of the penguins, which included aggressive threat displays and blows. Not surprisingly, they found that penguins participating in fights had faster heart rates than when they were standing still. Physical movement causes heart rate to rise, so this result is expected.
However, they also found that bystanders near the fights had elevated heart rates. The researchers suggest that this might be because fights present a risk to bystanders too: redirected aggression is common in King Penguin conflicts, and bystanders often end up being pulled into the fight. Stress at the anticipation of this might raise their heart rates. This is a cost of group living that we might overlook if we didn’t have heart rate data: the bystanders don’t look like they’re being affected by fights, as long as they don’t get involved, but it turns out that even those who don’t get pulled into a fight may incur increased stress.
The researchers also found that heart rate may indicate something about the intention of a penguin. In fights with blows, the penguin who initiated the blows had a higher heart rate than the penguin who simply fought back. Of course, we cannot yet know why this is – perhaps thinking about striking a blow raises one’s heart rate; perhaps higher heart rate indicates more stress, and more-stressed birds are more likely to strike – but it is tantalizingly close to having a glimpse into how a bird experiences the world, and how it decides how to respond.
Photo note: Liam Quinn’s photography can be found on Flickr here.