Regular ArticleDivorce in the long-lived and monogamous oystercatcher, Haematopus ostralegus: incompatibility or choosing the better option?
Abstract
Abstract. Oystercatchers breeding on Schiermonnikoog divorced, because one of the mates deserted (leaving the partner as a victim of its choice), or because one or both mates were chased from the territory by usurpers. Though the majority of divorced birds were classified as victims, among birds that retained breeding status females more often chose to divorce than did males. Females changing mates were also more likely to move between territories than were males. A much larger database from Skokholm showed that the reproductive success of new pairs, which depended on the breeding history of the female only, was lower than that of old pairs. The suggestion that females benefited from divorce depended on the interpretation of the decrease in reproductive success with the new mate for widowed birds as an efficiency cost of mate change. However, the increase in reproductive success with duration of the pair bond for female first-time breeders and divorced females (but not for widowed females) may be linked to an increase in breeding age of the female, instead of a re-bound from initial inefficiency in reproduction with the new mate. Hence, competition for good mates and/or good territories appears the primary constraint on options for mate change for both males and females. The role of active choice and competition for good mates and/or good territories has been neglected in previous studies of divorce. The better option hypothesis takes account of both.
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Go your own way? Reasons for divorce in a monogamous seabird
2023, Animal BehaviourPair bond duration is usually associated with reproductive success in long-lived monogamous species, yet pairs sometimes divorce. Possible explanations for divorce include having access to a higher-quality partner or territory, selecting a more compatible partner, asynchronous arrival at the breeding site or displacement of one member of a pair by an intruder. Factors influencing the occurrence of divorce are still unknown for many bird species, although divorce is often associated with low reproductive success in the preceding year. The thick-billed murre, Uria lomvia, is a colonial long-lived seabird species that has biparental care and undergoes occasional divorce. In this study, we investigated factors influencing the occurrence of divorce as well as the impact of divorce on subsequent reproductive success using data collected over 24 years at a breeding colony on Coats Island (Nunavut, Canada). Yearly divorce rate averaged 9%. The probability of divorce decreased with breeding experience/age, nest site quality and successful fledging in the previous year. Both sexes initiated divorce. Divorced birds did not obtain a better partner or improve their nesting site quality. Divorce seemed to be triggered by low reproductive success rather than a new partner or nesting site opportunity. Finally, an initial reduction of reproductive success was found for birds that divorced. Our findings help to understand the triggers and consequences of mate changes in long-lived monogamous species.
Sex-specific fitness consequences of mate change in Scopoli's shearwater, Calonectris diomedea
2023, Animal BehaviourSocial monogamy is the most common social mating system in birds. However, the persistence of pair bonds between breeding seasons varies among species, populations and individuals. Understanding fitness causes and consequences of mate change is critical for understanding population dynamics and the evolution of social monogamy. We used 12 years of data from Scopoli's shearwater breeding population to estimate mate change probabilities and test whether they affect the probabilities of (1) skipping breeding, (2) apparent survival and (3) breeding success. Widowing was the most common cause of mate change, with more males changing mates at least once in their lives than females. Females' probability of skipping a breeding season increased significantly just before pairing with a new partner. Also, we found that females' apparent survival, but not males', might increase after mate change. A possible explanation is that a longer adult life expectancy of females after mate change could at least partially offset the cost of skipping breeding. We found no relation between mate change and breeding success. Our study suggests that the costs and benefits of mate fidelity may be sex specific in this species. Future research on this topic should focus on the effects of mate change on each sex's lifetime reproductive success, which we could not address specifically in this study. Future studies will hopefully be able to delve deeper into how mate change, caused by divorce or widowhood, shifts the balance of reproduction or survival, determining lifetime reproductive success.
Should I stay or should I go: factors influencing mate retention and divorce in a colonial seabird
2022, Animal BehaviourDivorce among serially monogamous birds can lead to increased reproductive success if an individual obtains a higher-quality mate or nest site, or it can lead to lower reproductive success due to lack of pair experience or reduced breeding opportunities. Identifying the drivers and consequences of mate retention and divorce are necessary then to understand population dynamics, particularly as animals may alter behaviours in response to climate-induced environmental changes. We used a 33-year data set from a declining Magellanic penguin, Spheniscus magellanicus, colony to identify drivers of mate retention and divorce and test whether the nature of those drivers differed between first-year and long-term pairs. In a pair's first year, breeding outcome was the most important predictor of whether mates would reunite: failure rates were high and 71% of first-year pairs divorced on the whole, but only 47% of pairs that fledged a chick divorced. For long-term pairs, both breeding outcome and between-season changes to nest quality were the most important predictors of whether a pair stayed together: pairs that had a chick hatch or fledge divorced at lower rates than those that failed at the egg stage, and pairs whose nest quality declined were more likely to divorce. We also examined the fitness consequences of divorce by comparing the rates at which females and males obtained new mates and fledged chicks in the following year. Although females were more likely than males to secure a new mate, both sexes experienced similarly increased reproductive success with their new mates compared to their old mates, showing that divorce is adaptive.
Divorce rate varies with fluidity of passerine social environment
2022, Animal BehaviourThe frequency of divorce in pair-bonding species should vary not only with the fitness costs of separating from suboptimal mates, but also with the opportunities for finding alternatives of higher quality or compatibility. Such opportunities should be more commonplace in group-living species, especially the fission–fusion groups that typify many social vertebrates. Here we tested the hypothesis that greater fluidity of the social environment results in higher divorce rates by altering flock composition of captive zebra finches, Taeniopygia guttata, soon after birds paired. Twelve flocks (10 males and 10 females per flock) were established in breeding aviaries and observed until 80% of birds in each flock paired. After removing birds that did not pair, flock composition was manipulated to achieve either a more fluid environment (by exchanging half the pairs between flocks) or a less fluid one (all pairs remained in their original flock); flock size was then restored to 20 birds by adding four new, unmated individuals. Following manipulation of group composition, some birds divorced and remated and, as predicted, most such instances (9 of 10 divorces) occurred in the higher fluidity treatment. Remated pairs took longer to initiate clutches and produced fewer offspring than stable pairs, supporting the idea that divorce has short-term costs. In the premanipulation phase of the experiment, members of pairs that subsequently divorced engaged in high levels of courtship/pairing activity, but they appeared not to resolve nest site selection. These findings support the behavioural incompatibility hypothesis as a driver of divorce. Results suggest that incidence of divorce in natural populations could be significantly higher than typically reported, given that shifts in mate affiliation relatively soon after pairing are seldom investigated. Findings also indicate that caution should be exercised regarding use of frequency of affiliative behaviours to quantify pair bond formation and strength.
The influence of pair duration on reproductive success in the monogamous ‘Alalā (Hawaiian crow, Corvus hawaiiensis)
2024, Frontiers in Conservation Science