Coordination in parental effort decreases with age in a long‐lived seabird

Abstract

Biparental care is widespread in avian species. Individuals may match the contribution of their partner, resulting in equal parental effort, or may exploit their partner, to minimise their own investment. These two hypotheses have received much theoretical and empirical attention in short‐lived species, that change mates between seasons. However, in species with persistent pair bonds, where divorce is rare and costly, selective pressures are different, as partners share the value of future reproduction. In such species, coordination has been suggested to be adaptive and to increase early in life, as a consequence of the importance of mate familiarity. However, as birds age, an increase in re‐pairing probability occurs in parallel to a decline in their survival probability. At the point when partners no longer share future reproductive success, exploitation of a partner could become adaptive, reducing selection for coordinated effort. As such, we suggest that coordination in parental effort will decline with age in long‐lived species. Using incubation bout duration data, estimated from salt‐water immersion bio‐loggers, deployed on black‐browed albatrosses Thalassarche melanophris, we examined the correlation in incubation bout durations for sequential bouts, as a measure of coordination. Our results show that coordination is highest in inexperienced pairs (early in reproductive life) and declines throughout the lifetime of birds. This suggests that both cooperation, indicated by coordinated effort, and conflict over care occurs in this species. We find no change in individual bout duration with increasing breeding experience, and hence no support for the hypothesis that aging leads to changes in individual incubation behaviour. This is, to our knowledge, the first study to demonstrate strong coordination in parental care when pairs share future reproductive success, but a decline in coordination with age, as sexual conflict increases.

Sex differences in parental response to offspring begging are associated with pair bond strength across birds

“…Parents may negotiate care indirectly through monitoring offspring (46)(47)(48) or directly through coordinating feeding visits or vocal communication (12,49,50). Males may also use parental care as a form of sexual signaling, if females preferentially mate with good fathers, as is found across fishes (51).…”

“…Conversely, species with strong (stable, monogamous) bonds would have more alignment of male and female future fitness, and fathers would have more paternity certainty, leading to higher male responsiveness and lower sex differences (2,12,23,32). Alternatively, because increased male care may allow females to breed again more quickly (as seen across mammals, 33), we hypothesized that males would be more responsive than females mostly in species with strong bonds.…”

“…Whichever parent abandons the nest first can mate again with a new partner, potentially doubling their reproductive output for the year, while the remaining parent must continue caring for the original brood (9). Many factors affecting the degree of sexual conflict over care and how much care each sex provides have been identified by theoretical models, notably the strength of pair bonds (2,(10)(11)(12)(13), sex ratio (3,14,15), and sex differences in the cost or ability to provide care (6,16,17).…”

Turn taking is not restricted by task specialisation but does not facilitate equality in offspring provisioning

“…Whether a species is more likely to cooperate or partially compensate will depend on a lot of factors (e.g. : environment, life history traits of a species, individual status such as age, social environment 46 – 48 ) and thus species might also vary along a continuum from being in conflict and cooperating 46 , 47 . In line with this, Lejeune et al found that in a population of blue tits, the ecological differences along an altitudinal gradient affected the pair coordination in synchrony and alternation 49 .…”

Simultaneous GPS-tracking of parents reveals a similar parental investment within pairs, but no immediate co-adjustment on a trip-to-trip basis

“…With the frequent occurrence of coordination among all these different seabird species, these studies altogether hint at the importance of cooperation between parents. However, they give little insight into how parental efforts are divided between the pair members as an important component, namely the foraging effort, is rarely studied in this context (but see [18,37]). Observing seabirds during their foraging trips remains difficult, meaning that important information on parental investment that occurs away from the nest is missed.…”