Divorce Is More Common In Albatross Couples With Shy Males, Study Finds

Most albatross mate for life, but shy males who avoid confrontation are more likely to be displaced by a more aggressive male, leading to divorce

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Wandering albatross, Diomedea exulans, usually mate for life. But whether an albatross pair remain together until “death us do part” mostly depends upon the male partner’s personality, according to a recently published study (ref). Surprisingly, this study found that shy males were more likely to be divorced.

“We thought that bold males, being more aggressive, would be more likely to divorce, because they would be more likely to take the risk of switching partners to improve future reproductive outcomes”, the study’s senior author, seabird ecologist Stéphanie Jenouvrier, said in a statement. Professor Jenouvrier is an associate scientist at Woods Hole Oceanographic Institute’s FLEDGE Lab where she is an expert in how climate change affects seabird populations.

“Instead, we find the shy [males] divorce more because they are more likely to be forced to divorce by a more competitive intruder”, Professor Jenouvrie continued.

This link between personality and divorce could help scientists predict the resilience of an albatross population over time.

“The wandering albatross is a vulnerable species”, said the lead author of the study, seabird biologist Ruijiao Sun, a PhD candidate in the MIT/Woods Hole Oceanographic Institution (MIT-WHOI) Joint Program. “Understanding the effect of personality on divorce is important because it can help researchers predict the consequences for population dynamics, and implement conservation efforts.”

Despite being the last species of albatross to be formally described by scientists, the wandering albatross is one of the largest and most studied species of birds in the world. The wandering albatross has the longest wingspan of any living bird, averaging around 3.05 m (10 ft) for adults from the Crozet Islands, and they can be found soaring around their huge circumpolar home range in the Southern Oceans (between 28° and 60°). Wandering albatrosses spend most of their life in flight and they travel vast distances in search of food. They are known to feed further out in open oceans than other albatross species.

Albatross come to land to breed on tiny subantarctic islands starting in early November. Wandering albatross incubation lasts about 11 weeks, involving both parents, and chick-rearing lasts up to 280 days, and so they tend to breed once every two years.

“Breeding is very costly to wandering albatross”, Ms Sun told me in email. “So individuals have to make a trade-off between reproduction and their own survival.”

“More than 80% of the birds take a sabbatical year after a breeding season”, Ms Sun added in email. “So in most of the cases, both partners take one year off and reunite a year after (although they do not feed in the same place during this sabbatical year).”

But sometimes, a female may stick around to squeeze in another breeding attempt after her mate departs for his sabbatical on the open sea.

“What’s interesting is that, some females do not take a sabbatical year and instead, they breed with a transient partner while their long-term partner skips breeding”, Ms Sun elaborated in email. “The females then reunite with their long-term partners and breed with them again. We call this ‘temporary divorce’.”

A long-term marking program has been in place since 1959 to monitor the wandering albatross population that nests on Possession Island in the Crozet Island Archipelago in the Southern Indian Ocean. Although wandering albatross nest on several nearby islands (and tend to remain faithful to the island of their birth), almost all of their populations are declining. In 1997, for example, it was estimated that roughly 2000 pairs of wandering albatross nested throughout the Crozet Islands, although their numbers decline nearly every year.

“This population of wandering albatross experience severe fishery bycatch (long-line fishing)”, Ms Sun told me in email. “Females and males forage in different foraging grounds, with the females’ foraging grounds overlapping more with fishing vessels.”

For this reason, fishery bycatch is the source of sex-biased mortality amongst the albatross nesting in the Crozet Islands since the 1970s, leading to a male-skewed sex ratio with a high proportion of widowed males (i. e.; ref). Many male albatross widows and divorcées on Possession Island are actively seeking a new mate, so the competition can be fierce, with some males aggressively trying to steal a female from another male in what the researchers’ refer to as a “forced divorce” (figure 1d).

To understand how personality affects divorce in albatross, the research team measured their boldness. To do this, a researcher would approach the incubating bird, stopping 5 meters (16.4 feet) away from the nest. The resulting behavioral response was classified on a scale of zero (extremely shy) to five (very bold).

Long term studies in this population of wandering albatross indicate this behavioral proxy of boldness is both highly repeatable and heritable (ref). Additionally, there is little evidence that boldness changes either with environmental conditions or as individual albatross grow older and wiser. Further, these personality traits correspond to predictable behaviors, such as males protecting their mates from competitors.

Long-term data found there were 71 divorces out of 490 records in females and 88 divorce events out of 622 in males. Data analysis found that even when controlling for breeding experience and the number of breeding attempts of a pair, shyer males had higher divorce rates than bolder males (Figure 2a), whereas this was not seen in females (Figure 2b).

“When there is a third intruder that competes, shy birds could step away and give away their mates, where bolder individuals are aggressive and will guard their partner and secure their partnership”, Ms Sun elaborated. “Shyer individuals tend to avoid risks and engaging in antagonistic interactions with intruders.”

Shy females, on the other hand, did not face the same high likelihood of divorce, probably because there is such an imbalance in sex ratios in this population, so a female could always find a temporary mate if she wanted one. But for divorced males, the study found that it can take them more than four years to find another mate.

These findings may not apply to albatross colonies with a more evenly matched ratio of breeding females to males because there would be less competition for mates, and less incentive for a ‘forced divorce.’

“We were able to study the impact of personality on divorce only because we had access to incredible long-term data sets combining demography and personality for this population”, Ms Sun said.

The Possession Island monitoring program has identified breeding albatross and their partners — and their divorces — and followed their breeding outcomes for 54 years. Additionally, field studies have been conducted on this population of albatross since 2008 by several researchers who also collaborated on this study to characterize the personality traits of nearly 2000 individual birds.

The researchers also found that divorce in albatross does not always result from a shy male. Divorce in wandering albatross can sometimes be adaptive, to gain a better partner or offspring (Figure 1b). Additionally, another study, published last year, found that climate change could also be driving albatross to divorce, because the birds have to travel farther to find decreasing amounts of food to feed their chick (ref).

The link between personality and relationship outcome is well-established in humans, but this is the first time a link between personality and divorce has been demonstrated in wild animals.

Ms Sun and her collaborators are now planning to examine how the personality of individuals affects how the larger population changes and evolves. For example, do different personality types lead to different demographic outcomes?

“[In this study] we’re talking about a connection between personality and divorce at the individual level”, Ms Sun said. “But we want to understand the impact at the population level.”

Sources:

Ruijiao Sun, Joanie Van de Walle, Samantha C. Patrick, Christophe Barbraud, Henri Weimerskirch, Karine Delord and Stéphanie Jenouvrier (2022). Boldness predicts divorce rates in wandering albatrosses (Diomedea exulans), Biology Letters | doi:10.1098/rsbl.2022.0301

Ruijiao Sun, Christophe Barbraud, Henri Weimerskirch, Karine Delord, Samantha C. Patrick, Hal Caswell, and Stéphanie Jenouvrier (2022). Causes and consequences of pair-bond disruption in a sex-skewed population of a long-lived monogamous seabird, Ecological Monographs 92:e1522 | doi:10.1002/ecm.1522


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