There’s something tender about penguin courtship—maybe even romantic. After spending months at sea chasing fish and swimming in the coldest waters, female Adélie penguins (Pygoscelis Adeliae) slither back to the same nesting sites year after year. As they waddle through a bar scene where the males play trumpets and preen, they ignore the advances and make their way to their pals from last season: the males who arrived before the females to clean up their nest.
These penguins are paragons of long-term commitment. But are all penguins equally attached to a single mate throughout their lives?
It turns out these penguins are the exception, not the rule. Although most penguins only mate with one mate per breeding season, they may mate with many other penguins in a breeding colony before settling down to nest. And accuracy rates vary widely from species to species. Penguins’ love—it’s complicated.
“The short answer is no, penguins aren’t really monogamous,” said Emma Marks, a behavioral ecologist at the University of Auckland in New Zealand who studies breeding behavior and mate choice in penguins. Colonial breeders — Birds that congregate in large colonies to nest. “Colonial breeders like penguins can be monogamous because they have a single mate with whom they nest and raise chicks each season,” Marks told Live Science. “But that doesn’t mean that ‘extramarital activities’ don’t exist.”
It can be said that penguins are not sexually monogamous. Many penguins play on the field before settling down with a mate for the season. They sometimes copulate with other members of the colony who have already been cast, which Marks says leads to drama worthy of a soap opera.
A consequence of these chaotic love triangles is that by the time a female lays her egg, it is not always clear whether the male she will be spending the season with is raising his own chick. A 2018 study published in the journal Zoo Biology described a gentoo penguin (Pygoscelis papua) in a Utah aquarium which, due to the promiscuity of its mate, ended up raising two chicks that were the offspring of another male. Scientists aren’t sure how common this phenomenon is in nature, because while tracers and other technologies can help researchers monitor mating behavior and pair formation, there hasn’t been a concerted effort to test paternity of chicks in the wild, they say the authors of the study.
At the same time, penguins are more or less socially monogamous. It takes two dedicated partners to raise a chick in an environment as harsh as Antarctica, and penguins pair up to effectively share the responsibilities of nest care, egg incubation, and hunting.
“Social monogamy is a prerequisite,” Marks said. “Raising chicks requires a lot of coordination between the two and if that went wrong the breed would be a failure for the season.”
These social arrangements can persist over the long term, with each breeding season resulting in the same two penguin parents returning to their nest for another year. The frequency with which this occurs depends in part on the species. A 2013 literature review published in the journal Comptes Rendus Biology showed that 89% of Galápagos penguins (Spheniscus mendiculus) stay true to their partner. In contrast, a 1999 study published in The Auk magazine showed that only 15% of emperor penguins (Aptenodytes forsteri) seek the same mate for subsequent breeding seasons. Most species return to the same mates at least reasonably consistently, according to the 2013 study, with fidelity rates ranging from 59% to 89%.
Last season’s success also plays a role in whether penguin couples stay together long-term, Marks says. If the pair has successfully raised chicks to maturity and the male maintains a quality nest in a good location, the chances of a female reverting to her former mate are generally higher. Otherwise, the females are just as likely to waddle in search of greener pastures.
“There are many options for colonial species,” Marks said. “If breeding has failed before, we generally expect more ‘divorces’ in the following season.”
Actual “divorce rates”, that is, instances when penguins actively leave former mates in favor of new conquests, are difficult to calculate because not all penguins return to the breeding grounds each season. . When new pairs form, it can be difficult to determine whether this is a personal decision or whether the penguin only moved on after its other half failed to return, for example because it was eaten by an orca or a seal.
Predators aren’t the only threat to penguins’ love lives. A recent study published in the journal Ambio found that penguin populations are declining in proportion to the decrease in the amount of krill available for food. According to the study, climate change and human fishing activities are the main causes of the decline in krill numbers. Climatic changes in sea ice also force penguins to travel to other breeding grounds, breaking up long-standing mating and influencing migration. According to Mr Marks, some males are now arriving at the breeding grounds exhausted from navigating the changing sea and ice landscape, too neglected to court females and too exhausted to properly care for the eggs.
Collectively, these factors are believed to have played a role in Halley Bay’s widely reported failure. The hatchery, which once hosted 25,000 pairs of emperor penguins per season, has been desolate since 2016.
“Climate change will likely reduce breeding colony success rates,” Marks said. “Whenever default rates are higher, we expect higher companion turnover rates.”