If the pairing is deemed to be sub-optimal, that is reproductive success is low, one bird (usually the female) will divorce their partner in order to establish a new partnership with improved reproduction. Divorce is thought to be driven by win-stay, loose-switch thinking, where previous breeding performance informs on the decision to remate or to leave. Divorce rates are also directly linked to environmental conditions, with rates increasing in poor quality environments.
A new study from the University of Lisbon looks at the temporal variability in divorce rates of 15,500 breeding pairs of Black-browed albatrosses from the Falkland Islands over 15 years. Annual divorce rates varied from 1% to 8%, with an average of 3.7%, the main trigger being reproductive failure. Females who failed during incubation were 5.2 and 5.4 times more likely to divorce their mate than those who failed to fledge their young or were successful, respectively.
Early failures are attributable to incompatibility or infertility. Individuals who did not breed or missed a breeding attempt were less likely to retain their mate than successful birds. Divorced females were more likely to breed with a new partner than males. The greater benefit females obtain from divorce suggest they are making the active decision to leave.
Divorce was found to be directly regulated by environmental variability, with higher rates in warmer years. Warmer seas are associated with reduced food availability, which lowers breeding success. Some females would leave their partner even if successful. The environment possibly acts directly upon the decision to leave by disrupting the win-stay, loose-switch thinking process. Whereby female decision making may become deluded and a lack of reproductive success mistakenly attributed to poor mate performance not body condition.
Unnecessary divorce and reduced reproductive success is concerning for seabirds and other monogamous species worldwide as climate change continues to drive up temperatures. As divorce rates increase and breeding success is reduced, populations will begin to fail.