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

Nest quality predicts the probability of egg loss in the critically endangered 'Alalā (Corvus hawaiiensis)

Conservation breeding programs for endangered species face challenges, notably in the development of husbandry techniques, complicated by the impracticality of conducting controlled experiments. To reduce uncertainty regarding what works in conservation breeding programs, it is essential to capture data. In avian breeding programs, the construction of quality nests and appropriate incubation and handling of eggs by the parents are essential prerequisites to the successful production of offspring. Here, we study factors influencing nest-building and parental incubation outcomes in 'alalā (Corvus hawaiiensis), which is extinct in the wild and numbers fewer than 130 individuals in human care. Using parent-incubated egg data from 2018 to 2021 (171 clutches, 55 pairs), we evaluated the role of husbandry factors in determining the quality of nests constructed by 'alalā and the likelihood of nest quality and other social and environmental factors to predict egg loss (breaking, cannibalization, or ejection of an egg from the nest). More than half of all eggs laid failed to reach the hatch date. Nest quality was the most influential predictor of egg loss, with eggs in higher quality nests more likely to reach the hatch date. Male age also influenced egg loss, with very young (3 years old) and older males (⪞12 years old) experiencing more egg loss. Furthermore, the two facilities and two aviary types also differed in the quality of nests 'alalā constructed, indicating that nest-building behavior can be influenced by husbandry practices. These findings reduce uncertainty and provide insights for recommended management interventions to facilitate successful reproduction in human care.

Individual consistency in the localised foraging behaviour of shy albatross (Thalassarche cauta)

Quantifying the intra- and interindividual variation that exists within a population can provide meaningful insights into a population's vulnerability and response to rapid environmental change. We characterise the foraging behaviour of 308 trips taken by 96 shy albatross (Thalassarche cauta) from Albatross Island across seven consecutive years. At a population level, incubating shy albatross exploited a consistent area within ca. 500 km radius of their breeding colony. During half of the trips, individuals utilised the closest shelf break to the west of the colony, where upwelling events have been reported. The other half of the trips were exclusively within the neritic zone, utilising a variety of locations within the Bass Strait. Furthermore, we found evidence of individual consistency to geographic locations, with subsequent trips by an individual more similar than random trips from all individuals in our data, both within and between years (G-test, p < .05). Between-individual variation in foraging behaviour was not meaningfully explained by age (linear regression, p > .05) or sex (t-test, p > .05) for any metric, suggesting that other intrinsic individual factors are accounting for between-individual variation in foraging trips. A localised foraging distribution is unusual for albatross, which, combined with high variation in space use between individuals demonstrated here, suggests that this species is accessing adequate resources near the colony. Overall, these findings suggest that incubating shy albatross from Albatross Island exhibit tendencies of a generalist population comprised of uniquely specialised individuals. These results suggest that this species is operating below its biological capacity in this fast-warming area and provide a baseline from which to assess future change.

Age effects on Nazca booby foraging performance are largely constant across variation in the marine environment: Results from a 5-year study in Galápagos

Foraging outcomes dictate the nutritional resources available to an organism and may vary with intrinsic factors, like age. Thus, understanding how age affects foraging performance, alone or in interaction with extrinsic factors (like environmental quality), improves our understanding of aging processes in the wild. We examined how foraging traits, measured across five breeding seasons, change with age, environmental variation, and their interaction in Nazca boobies (Sula granti), a pelagic seabird in Galápagos. We evaluated the hypotheses that (1) foraging performance is better in middle-aged birds than in young ones, and that (2) foraging performance is better in middle-aged birds than in old ones. Furthermore, favorable environmental conditions will either (3) attenuate age differences in foraging performance (by relieving constraints on young, inexperienced and old, senescent age classes), or (4) accentuate age differences (if middle-aged birds can exploit abundant resources better than other age classes can). Incubating birds tagged with GPS loggers (N = 815) provided data on foraging performance (e.g., total distance traveled, mass gained) to evaluate interactions between age and environmental variation (e.g., sea surface temperature). Poor environmental conditions associated with the cool phase of the El Niño-Southern Oscillation increased foraging effort, including foraging distance and duration, for example. Across age classes, foraging boobies responded similarly to environmental variation except for female mass gain rate: age-related declines in mass gain rate were reduced under favorable environmental conditions. Birds of different ages also searched in somewhat distinct areas in the poor conditions of 2016, but not in other years. In several foraging traits, including foraging duration and distance, female boobies showed predicted early-life improvement and late-life decline, following the established pattern for reproductive traits in this species. Thus, deficits in resource acquisition (this study) may contribute to the poor survival and reproductive outcomes previously observed in old Nazca boobies, particularly in females.

Partner intrinsic characteristics influence foraging trip duration, but not coordination of care in wandering albatrosses Diomedea exulans

Long-lived monogamous species gain long-term fitness benefits by equalizing effort during biparental care. For example, many seabird species coordinate care by matching foraging trip durations within pairs. Age affects coordination in some seabird species; however, the impact of other intrinsic traits, including personality, on potential intraspecific variation in coordination strength is less well understood. The impacts of pair members' intrinsic traits on trip duration and coordination strength were investigated using data from saltwater immersion loggers deployed on 71 pairs of wandering albatrosses Diomedea exulans. These were modeled against pair members' age, boldness, and their partner's previous trip duration. At the population level, the birds exhibited some coordination of parental care that was of equal strength during incubation and chick-brooding. However, there was low variation in coordination between pairs and coordination strength was unaffected by the birds' boldness or age in either breeding stage. Surprisingly, during incubation, foraging trip duration was mainly driven by partner traits, as birds which were paired to older and bolder partners took shorter trips. During chick-brooding, shorter foraging trips were associated with greater boldness in focal birds and their partners, but age had no effect. These results suggest that an individual's assessment of their partner's capacity or willingness to provide care may be a major driver of trip duration, thereby highlighting the importance of accounting for pair behavior when studying parental care strategies.

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

Sexual conflict arises when two individuals invest in their common offspring because both individuals benefit when their partner invests more. Conditional cooperation is a theoretical concept that could resolve this conflict. Here, parents are thought to motivate each other to contribute to provisioning visits by following the rules of turn taking, which results in equal and efficient investment. However, parents have other tasks besides provisioning, which might hinder taking turns. To investigate restrictions by other care tasks and whether turn taking can be used to match investment, we manipulated brooding duration in female blue tits (Cyanistes caeruleus) during the early nestling phase by changing nest box temperature. As expected, females subjected to cold conditions brooded longer than females under warm conditions. Yet, contrary to our prediction, females had similar visit rates in both treatments, which suggests that females in the cold treatment invested more overall. In addition, the females' turn taking level was higher in the more demanding cold condition (and the calculated randomised turn taking levels of females did not differ), hence females don't seem to be restricted in their turn taking strategy by other care tasks. However, males did not seem to match the females' turn taking levels because they did not adjust their visit rates. Thus, level of turn taking was not restricted by an other sex-specific task in females and did not facilitate a greater investment by their male partners.

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

BACKGROUND

Parental care benefits the offspring, but comes at a cost for each parent, which in biparental species gives rise to a conflict between partners regarding the within-pair distribution of care. Pair members could avoid exploitation by efficiently keeping track of each other's efforts and coordinating their efforts. Parents may, therefore, space their presence at the nest, which could also allow for permanent protection of the offspring. Additionally, they may respond to their partner's previous investment by co-adjusting their efforts on a trip-to-trip basis, resulting in overall similar parental activities within pairs.

METHODS

We investigated the coordination of parental care measured as nest attendance and foraging effort in the Lesser black-backed gull (Larus fuscus), a species with long nest bouts that performs extended foraging trips out of sight of their partner. This was achieved by GPS-tracking both pair members simultaneously during the entire chick rearing period.

RESULTS

We found that the timing of foraging trips (and hence nest attendance) was coordinated within gull pairs, as individuals left the colony only after their partner had returned. Parents did not match their partner's investment by actively co-adjusting their foraging efforts on a trip-by-trip basis. Yet, pair members were similar in their temporal and energetic investments during chick rearing.

CONCLUSION

Balanced investment levels over a longer time frame suggest that a coordination of effort may not require permanent co-adjustment of the levels of care on a trip-to-trip basis, but may instead rather take place at an earlier stage in the reproductive attempt, or over integrated longer time intervals. Identifying the drivers and underlying processes of coordination will be one of the next necessary steps to fully understand parental cooperation in long-lived species.