Study finds divorce more common among albatross pairs with shy males MIT News

The wandering albatross is the poster bird for monogamous birds. Graceful gliders have been known to mate for life, and share the same bird to breed, season after season, between long journeys at sea.

But on rare occasions, the albatross “releases”—a term ornithologists use for situations in which one partner leaves the pair for another pair while the other partner remains in the flock. Divorce rates vary widely around the world, and the divorce rate for wandering albatross is relatively low.

However, floating giants can separate. Scientists at the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution (WHOI) have found that, at least for a certain group of wandering albatrosses, whether a spouse will divorce boils down to one important factor: personality.

In a study appearing today in the journal Biology LettersThe team reported that the couple’s chance of divorce is strongly influenced by the “audacity” of the male partner. The more bold and aggressive the male, the more likely the pair will survive together. The more shy the male, the greater the chance that the spouses will divorce.

The researchers say their study is the first to link personality and divorce in a wild animal species.

“We thought that bold males, being more aggressive, would be more likely to divorce, because they would be more likely to risk switching partners to improve future reproductive outcomes,” says senior study author Stephanie Jenoferre, co-scientist and seabird ecologist at WHOI’s FLEDGE Laboratory. Instead, we find shy divorcers more because they are more likely to be forced into divorce by a more competitive intruder. We expect personality to affect divorce rates in many species, but in different ways.”

Lead author Ruijiao Sun, a graduate student in the joint MIT-WHOI program and MIT’s Department of Earth, Atmospheric and Planetary Sciences, says this new evidence of a link between personality and divorce in wandering albatrosses may help scientists predict population resilience.

“Wandering albatrosses is an endangered species,” Sun says. “Understanding the impact of personality on divorce is important because it can help researchers anticipate consequences for population dynamics, and implement conservation efforts.”

Study co-authors are Joanie Van de Walle of WHOI, Samantha Patrick of the University of Liverpool, Christophe Barbroude, Henri Weimerskirche and Karen DeLord of CNRS-University of La Rochelle in France.

Repeat divorced

The new study focuses on a group of wandering albatrosses that regularly return to Position Island in the southern Indian Ocean to breed. This group was the focus of a long-term study dating back to the 1950s, in which researchers monitored the birds each breeding season and recorded the pairs and separations of individuals over the years.

This particular group tends toward male individuals more than females because female albatross foraging areas overlap with fishing vessels, where they are more likely to be accidentally caught in fishing lines as bycatch.

In previous research, Sun analyzed data from this long-term study and discovered an intriguing pattern: These divorced individuals were more likely to do so over and over again.

“Then we wanted to know, what drives divorce, and why some individuals divorce so often,” says Genouvrier. “In humans, you also see this frequent divorce pattern associated with personality. The wandering albatross is one of the rare species for which we have demographic and personality data.”

This personality data comes from an ongoing study that began in 2008 led by co-author Patrick, who was measuring the personality of individuals among the same group of roaming albatrosses on Possession Island. In the study of animal behavior, personality is defined as a consistent behavioral variation exhibited by an individual. Biologists mainly measure personality in animals as a gradation between shy and bold, or less to more aggressive.

In Patrick’s study, researchers measured grit in albatrosses by measuring a bird’s reaction to a human approaching its nest, from a distance of about 5 metres. A bird is assigned a score depending on how it reacts (a bird that does not respond scores a zero, being the most shy, while a bird that raises its head, and even stands, can score higher, being the most daring).

Patrick conducted multiple personal evaluations of the same individuals over several years. Sun and Jenniferre wondered: Could an individual’s personality have anything to do with their chance of divorce?

“We saw this recurring pattern of divorce, and then spoke with Sam (Patrick) to see, could this be related to the character?” You remember the sun. “We know that personality predicts divorce in humans, and it would be self-evident to associate personality with divorce in wild populations.”

shy birds

In their new study, the team used data from both demographic and personality studies to see if any patterns emerged between the two. They applied a statistical model to the two data sets, to test whether the personality of individuals in an albatross pair influenced the fate of that pair.

They found that for females, personality had nothing to do with whether the birds were shooting or not. But in males, the pattern was clear: those identified as shy were more likely to divorce, while bolder males stayed with their partners.

“Divorce doesn’t happen very often,” says Jenouvrier. “But we found that the more shy the bird, the more likely it was to divorce.”

but why? In their study, the team offers an explanation that ecologists call “forced divorce.” They point out that in this particular group of roving albatrosses, males far outnumber females and are therefore more likely to compete with each other for mates. Therefore, males who have already entered into a partnership may encounter a third “intruder” – a man competing for a place in the pair.

“When there is a third intruder competing, shy birds can turn away and abandon their mates, as bolder individuals are aggressive and will guard their partner and secure their partnership,” explains Sun. “This is why divorce rates may be higher in shy individuals.”

The team plans to expand their work to examine how individuals’ personality can influence how a larger population changes and develops.

“We’re now talking about the relationship between personality and divorce on an individual level,” Sun says. “But we want to understand the impact at the population level.”

This research was supported, in part, by the National Science Foundation.

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