Study

Divorce in king penguins: asynchrony, expensive fat storing and ideal free mate choice

Olsson, Olof

Oikos, 1998

Peer-reviewedlongitudinal studywild

What they did

Individually marked king penguins were followed across breeding seasons, recording whether birds re-paired with the previous season's partner and relating the outcome to arrival timing and body condition.

Studied in: Aptenodytes patagonicus
Sample size: marked breeding pairs followed across seasons

What they found

Most pairs did not re-form in the following season. Divorce was strongly associated with asynchronous arrival: a bird ready to breed does not wait for a late partner, because the breeding cycle in this species is long and a delayed start fails. Fidelity was not driven by attachment but by timing.

What it means

The authors' reading, and ours. Where they differ, that difference is the point.

How the authors put it

Divorce rate in king penguins is largely a consequence of arrival asynchrony under a tight breeding schedule rather than of mate quality assessment.

How NatureHQ reads it

This is the study that makes "penguins mate for life" untenable as a general statement, and it explains why in a way that is more interesting than the correction. The birds are not fickle. The schedule is unforgiving, and a partner who has not arrived is a partner who cannot be waited for. Fidelity across penguin species tracks how much slack the breeding calendar has, which is why some species re-pair reliably and others almost never do. The claim is not false everywhere; it is false as a fact about penguins.

Limitations

One species; fidelity varies widely across penguins and this is at the low end.
Birds not seen again may have died rather than divorced, which inflates estimated divorce.
Observational, so the association with arrival timing is not experimentally manipulated.