Akiko Shoji

Lower foraging efficiency in immatures drives spatial segregation with breeding adults in a long-lived pelagic seabird

Competition and, ultimately, adaptive specialization are the major ecological forces behind spatial segregation in foraging distributions, and are commonly driven by size-related differences in competitiveness between individuals of different sex, age or social status. However, such segregation can also be observed in long-lived monomorphic species, often between immature and breeding individuals. In many of these species, individuals often forage in patchy and potentially unpredictable environments in which resources can be spread over large scales and be difficult to find, and efficient foraging may require advanced cognitive skills (for example in navigation and memory). Particularly in species with deferred breeding, experience rather than size may be an important driver of segregation and may lead to differences in competitiveness between young and old, but whether there is a relationship between age, foraging efficiency and spatial segregation has never been properly investigated. Here we tested this hypothesis by simultaneously tracking individuals at different life stages in a long-lived seabird, the Manx shearwater, Puffinus puffinus, during a period of central-place foraging around the colony, to investigate spatial segregation, and by measuring foraging efficiency by combining an ethoinformatics approach and mass gain. We found substantial spatial segregation between immature and breeding adults. Compared with adults, immatures gained less mass per unit of time spent foraging and foraged in less productive waters, suggesting lower foraging efficiency, probably because of inexperience.

Dual foraging and pair coordination during chick provisioning by Manx shearwaters: empirical evidence supported by a simple model

ABSTRACT The optimal allocation of time and energy between ones own survival and offspring survival is critical for iteroparous animals, but creates a conflict between what maximises the parents fitness and what maximises fitness of the offspring. For central-place foragers, provisioning strategies may reflect this allocation, while the distance between central-places and foraging areas may influence the decision. Nevertheless, few studies have explored the link between life history and foraging in the context of resource allocation. Studying foraging behaviour alongside food load rates to chicks provides a useful system for understanding the foraging decisions made during parent–offspring conflict. Using simultaneously deployed GPS and time–depth recorders, we examined the provisioning strategies in free-living Manx shearwaters Puffinus puffinus, which were caring for young. Our results showed a bimodal pattern, where birds alternate short and long trips. Short trips were associated with higher feeding frequency and larger meals than long trips, suggesting that long trips were performed for self-feeding. Furthermore, most foraging was carried out within 100 km of sea fronts. A simple model based on patch quality and travel time shows that for Manx shearwaters combining chick feeding and self-maintenance, bimodal foraging trip durations optimise feeding rates. Summary: A simple model based on patch quality and travel time shows that for Manx shearwaters combining chick feeding and self-maintenance, bimodal foraging trip durations optimise feeding rates.

Carry-over effects on the annual cycle of a migratory seabird: an experimental study

Summary Long‐lived migratory animals must balance the cost of current reproduction with their own condition ahead of a challenging migration and future reproduction. In these species, carry‐over effects, which occur when events in one season affect the outcome of the subsequent season, may be particularly exacerbated. However, how carry‐over effects influence future breeding outcomes and whether (and how) they also affect behaviour during migration and wintering is unclear. Here we investigate carry‐over effects induced by a controlled, bidirectional manipulation of the duration of reproductive effort on the migratory, wintering and subsequent breeding behaviour of a long‐lived migratory seabird, the Manx shearwater Puffinus puffinus. By cross‐fostering chicks of different age between nests, we successfully prolonged or shortened by ∼25% the chick‐rearing period of 42 breeding pairs. We tracked the adults with geolocators over the subsequent year and combined migration route data with at‐sea activity budgets obtained from high‐resolution saltwater‐immersion data. Migratory behaviour was also recorded during non‐experimental years (the year before and/or two years after manipulation) for a subset of birds, allowing comparison between experimental and non‐experimental years within treatment groups. All birds cared for chicks until normal fledging age, resulting in birds with a longer breeding period delaying their departure on migration; however, birds that finished breeding earlier did not start migrating earlier. Increased reproductive effort resulted in less time spent at the wintering grounds, a reduction in time spent resting daily and a delayed start of breeding with lighter eggs and chicks and lower breeding success the following breeding season. Conversely, reduced reproductive effort resulted in more time resting and less time foraging during the winter, but a similar breeding phenology and success compared with control birds the following year, suggesting that ‘positive’ carry‐over effects may also occur but perhaps have a less long‐lasting impact than those incurred from increased reproductive effort. Our results shed light on how carry‐over effects can develop and modify an adult animals behaviour year‐round and reveal how a complex interaction between current and future reproductive fitness, individual condition and external constraints can influence life‐history decisions.

Drivers and fitness consequences of dispersive migration in a pelagic seabird

Lay Summary Sex segregation, competition and differences in individual quality may drive dispersive migration in birds and affect their fitness. Atlantic puffins tracked for up to 6 years followed remarkably different migration routes, but individuals followed the same route every year. Although random dispersion and sex segregation could not explain the patterns observed, birds visiting the Mediterranean Sea foraged more and had a higher breeding success than birds remaining locally or visiting the Atlantic Ocean.

Breeding phenology and winter activity predict subsequent breeding success in a trans-global migratory seabird.

Inter-seasonal events are believed to connect and affect reproductive performance (RP) in animals. However, much remains unknown about such carry-over effects (COEs), in particular how behaviour patterns during highly mobile life-history stages, such as migration, affect RP. To address this question, we measured at-sea behaviour in a long-lived migratory seabird, the Manx shearwater (Puffinus puffinus) and obtained data for individual migration cycles over 5 years, by tracking with geolocator/immersion loggers, along with 6 years of RP data. We found that individual breeding and non-breeding phenology correlated with subsequent RP, with birds hyperactive during winter more likely to fail to reproduce. Furthermore, parental investment during one year influenced breeding success during the next, a COE reflecting the trade-off between current and future RP. Our results suggest that different life-history stages interact to influence RP in the next breeding season, so that behaviour patterns during winter may be important determinants of variation in subsequent fitness among individuals.

High Corticosterone, Not High Energy Cost, Correlates with Reproductive Success in the Burrow-Nesting Ancient Murrelet

Theory and observations suggest that offspring abandonment in animals may occur when the costs to future reproductive output of current reproductive effort outweigh the fitness benefits of rearing the current brood. While hormonal cues (i.e. corticosterone) or energy reserves are believed to be involved, few studies have directly focused on the proximate cues influencing behaviours directly related to reproductive success. To address this information gap, we determined the incubation metabolic rates and corticosterone (CORT) levels of naturally fasting and freely incubating ancient murrelets (Synthliboramphus antiquus). Respiratory quotient (RQ) increased with date, suggesting that incubating ancient murrelets shifted from strictly lipid-based metabolism towards more protein-based metabolism as incubation progressed. Birds that hatched only one nestling had higher levels of circulating CORT than those which hatched two, suggesting that birds which laid only a single egg found incubation more stressful than those which laid two. However, CORT levels and incubation shift lengths were not correlated, suggesting that birds that undertook prolonged incubation shifts did so only when their energy stores were not jeopardized.

Comparing Methods for Monitoring Nest Attendance in Ancient Murrelets

Abstract. Knock-down tags are often used to monitor population and nest attendance patterns of burrow-nesting seabirds. However, the accuracy of the knock-down method has not been considered in detail. Here, measurements of nest attendance patterns for Ancient Murrelets (Synthliboramphus antiquus) obtained by the knock-down and the radio telemetry methods were compared on a colony at Reef Island, Haida Gwaii, Canada. Radio transmitters and knock-down tags both indicated activity 79% of the time (range: 61–96%, N = 307), and the correlation between the two methods was significant. Hence, knock-down tags provide information that, although coarse, can provide an adequate indication of reproductive behavior in Ancient Murrelets without disturbance to the bird.

Remotely sensed wind speed predicts soaring behaviour in a wide-ranging pelagic seabird

Global wind patterns affect flight strategies in many birds, including pelagic seabirds, many of which use wind-powered soaring to reduce energy costs during at-sea foraging trips and migration. Such long-distance movement patterns are underpinned by local interactions between wind conditions and flight behaviour, but these fine-scale relationships are far less well understood. Here we show that remotely sensed ocean wind speed and direction are highly significant predictors of soaring behaviour in a migratory pelagic seabird, the Manx shearwater (Puffinus puffinus). We used high-frequency GPS tracking data (10 Hz) and statistical behaviour state classification to identify two energetic modes in at-sea flight, corresponding to flap-like and soar-like flight. We show that soaring is significantly more likely to occur in tailwinds and crosswinds above a wind speed threshold of around 8 m s−1, suggesting that these conditions enable birds to reduce metabolic costs by preferentially soaring over flapping. Our results suggest a behavioural mechanism by which wind conditions may shape foraging and migration ecology in pelagic seabirds, and thus indicate that shifts in wind patterns driven by climate change could impact this and other species. They also emphasize the emerging potential of high-frequency GPS biologgers to provide detailed quantitative insights into fine-scale flight behaviour in free-living animals.

Predicting animal behaviour using deep learning: GPS data alone accurately predict diving in seabirds

To prevent further global declines in biodiversity, identifying and understanding key habitats is crucial for successful conservation strategies. For example, globally, seabird populations are under threat and animal movement data can identify key at-sea areas and provide valuable information on the state of marine ecosystems. To date, in order to locate these areas, studies have used global positioning system (GPS) to record position and are sometimes combined with time–depth recorder (TDR) devices to identify diving activity associated with foraging, a crucial aspect of at-sea behaviour. However, the use of additional devices such as TDRs can be expensive, logistically difficult and may adversely affect the animal. Alternatively, behaviours may be resolved from measurements derived from the movement data alone. However, this behavioural analysis frequently lacks validation data for locations predicted as foraging (or other behaviours). Here, we address these issues using a combined GPS and TDR dataset from 108 individuals by training deep learning models to predict diving in European shags, common guillemots and razorbills. We validate our predictions using withheld data, producing quantitative assessment of predictive accuracy. The variables used to train these models are those recorded solely by the GPS device: variation in longitude and latitude, altitude and coverage ratio (proportion of possible fixes acquired within a set window of time). Different combinations of these variables were used to explore the qualities of different models, with the optimum models for all species predicting non-diving and diving behaviour correctly over 94% and 80% of the time, respectively. We also demonstrate the superior predictive ability of these supervised deep learning models over other commonly used behavioural prediction methods such as hidden Markov models. Mapping these predictions provides useful insights into the foraging activity of a range of seabird species, highlighting important at sea locations. These models have the potential to be used to analyse historic GPS datasets and further our understanding of how environmental changes have affected these seabirds over time.

Coordinated provisioning in a dual-foraging pelagic seabird

In long-lived species, care-giving parents are expected to balance their own condition with that of their offspring. Many species of seabirds display a unique behavioural adaptation for managing these conflicting demands known as dual foraging, in which long trips, largely for self-maintenance, are alternated with short trips, which are primarily for offspring care. While dual foraging is a widely studied behaviour, it entails a complication that is seldom discussed: if parents independently employ a dual-foraging strategy, chicks might be abandoned for extended periods when the long trips of both partners coincide. Whether partners coordinate their dual-foraging strategies, however, is largely unknown. To investigate this possibility, we used radiofrequency identification readers coupled with passive integrated transponder tags to record extended sequences of foraging trips for breeding Manx shearwaters, Puffinus puffinus. Our results show a pattern of foraging trips that indicates a high level of coordination between parents, which facilitates consistent provisioning. Additionally, we show that the propensity for pairs to coordinate declines across the chick-rearing period. Given the potential costs of not coordinating, we expect this behaviour to be widely spread among dual-foraging species.