Drivers of ocean movement patterns in Round Island petrels

Among migratory bird species, shifts in phenology and distribution in response to changing environmental conditions are occurring across the world. Understanding the mechanisms through which these shifts occur, and thus the consequences for species conservation, relies on knowing the extent of within- and between-individual variation in migratory strategies, and their consequences for the conditions experienced by individuals. In this thesis, I use a global, multi-species, meta-analytical approach of published studies, a long-term (2009-2019) geolocator tracking dataset from a well-studied population of Pterodroma petrels on Round Island, Mauritius, in the tropical western Indian Ocean, and a field study of remote monitoring of petrel breeding ecology to explore these issues. These approaches revealed that repeatability in migratory timings is a common feature of avian migratory systems, yet is poorly studied in tropical systems, where resources are often patchy and unpredictable. Round Island petrel tracking helps to fill this knowledge gap, and their unusual hybrid status, year-round breeding, and monsoon-driven seasonal environment make them a model species for such questions. Repeat tracking of individual petrels revealed low levels of within-individual variation in migratory behaviour, but very high levels of between-individual variation, with petrels occurring across the Indian Ocean. Despite the huge area over which non-breeding petrels occur, petrel night-time activity patterns closely tracked the lunar cycle in all cases, including in migratory strategies used by very few tracked individuals. Deployment of remote cameras was successful at capturing individual petrel breeding events and citizen science processing of images produced only slightly lower estimates of breeding activity. Overall, the work in this thesis contributes to the understanding of migratory systems and how they can change, and of the conditions experienced by tropical seabirds

Individual repeatability of avian migration phenology: a systematic review and meta-analysis

Changes in phenology and distribution are being widely reported for many migratory species in response to shifting environmental conditions. Understanding these changes and the situations in which they occur can be aided by understanding consistent individual differences in phenology and distribution and the situations in which consistency varies in strength or detectability. Studies tracking the same individuals over consecutive years are increasingly reporting migratory timings to be a repeatable trait, suggesting that flexible individual responses to environmental conditions may contribute little to population-level changes in phenology and distribution. However, how this varies across species and sexes, across the annual cycle and in relation to study (tracking method, study design) and/or ecosystem characteristics is not yet clear. Here, we take advantage of the growing number of publications in movement ecology to perform a phylogenetic multilevel meta-analysis of repeatability estimates for avian migratory timings to investigate these questions. Of 2,433 reviewed studies, 54 contained suitable information for meta-analysis, resulting in 177 effect sizes from 47 species. Individual repeatability of avian migratory timings averaged 0.414 (95% confidence interval: 0.3-0.5) across landbirds, waterbirds and seabirds, suggesting consistent individual differences in migratory timings is a common feature of migratory systems. Timing of departure from the non-breeding grounds was more repeatable than timings of arrival at or departure from breeding grounds, suggesting that conditions encountered on migratory journeys and outcome of breeding attempts can influence individual variation. Population-level shifts in phenology could arise through individual timings changing with environmental conditions and/or through shifts in the numbers of individuals with different timings. Our findings suggest that, in addition to identifying the conditions associated with individual variation in phenology, exploring the causes of between-individual variation will be key in predicting future rates and directions of changes in migratory timings. We therefore encourage researchers to report the within- and between- individual variance components underpinning the reported repeatability estimates to aid interpretation of migration behaviour. In addition, the lack of studies in the tropics means that levels of repeatability in less strongly seasonal environments are not yet clear

DNA diet profiles with high‐resolution animal tracking data reveal levels of prey selection relative to habitat choice in a crepuscular insectivorous bird

Given the global decline of many invertebrate food resources, it is fundamental to understand the dietary requirements of insectivores. We give new insights into the functional relationship between the spatial habitat use, food availability, and diet of a crepuscular aerial insectivore, the European Nightjar (Caprimulgus europaeus) by relating spatial use data with high‐throughput sequencing (HTS) combined with DNA metabarcoding. Our study supports the predictions that nightjars collect a substantial part of their daily nourishment from foraging locations, sometimes at considerable distance from nesting sites. Lepidopterans comprise 65% of nightjars' food source. Nightjars tend to select larger species of Lepidoptera (>19 mm) which suggests that nightjars optimize the efficiency of foraging trips by selecting the most energetically favorable—larger—prey items. We anticipate that our findings may shed additional light on the interactions between invertebrate communities and higher trophic levels, which is required to understand the repercussions of changing food resources on individual‐ and population‐level processes

Twitter conferences as a low‐carbon, far‐reaching and inclusive way of communicating research in ornithology and ecology

Academic conferences play an important role in the scientific community by providing an opportunity for researchers to discuss their work and to network. However, drawbacks of traditional face-to-face (F2F) conferences, such as the ostensible exclusion of non-scientists, the substantial environmental footprint, and the large costs in terms of both time and money are increasingly being recognized. As a result, alternative and complementary formats are being explored. One of these is the Twitter conference (TC), in which research is presented and discussed on the social media platform Twitter. Here, we use hashtag and presenter data from several ornithology and ecology conferences (both TCs and F2F events) to explore the potential reach of the tweets and the magnitude of the difference in greenhouse gas emissions between the two conference types. We found that TCs generated greater engagement than F2F events, have the potential to reach a very large audience and result in a substantial reduction in emissions. Further, we argue that the format promotes presenter and audience diversity due to participation being flexible and virtually cost-free. While we recognize some disadvantages of this format compared to F2F events, especially in relation to the social and networking aspects of conferences, we envision that virtual events, such as TCs, will play an important role in the future of science dissemination and outreach. By embracing such opportunities, academic conferences can move towards a more inclusive and sustainable future

Individual consistency in migration strategies of a tropical seabird, the Round Island petrel

Background: In migratory species, the extent of within- and between-individual variation in migratory strategies can influence potential rates and directions of responses to environmental changes. Quantifying this variation requires tracking of many individuals on repeated migratory journeys. At temperate and higher latitudes, low levels of within-individual variation in migratory behaviours are common and may reflect repeated use of predictable resources in these seasonally-structured environments. However, variation in migratory behaviours in the tropics, where seasonal predictability of food resources can be weaker, remains largely unknown. Methods: Round Island petrels (Pterodroma sp.) are tropical, pelagic seabirds that breed all year round and perform long-distance migrations. Using multi-year geolocator tracking data from 62 individuals between 2009 and 2018, we quantify levels of within- and between-individual variation in non-breeding distributions and timings. Results: We found striking levels of between-individual variation in at-sea movements and timings, with non-breeding migrations to different areas occurring across much of the Indian Ocean and throughout the whole year. Despite this, repeat-tracking of individual petrels revealed remarkably high levels of spatial and temporal consistency in within-individual migratory behaviour, particularly for petrels that departed at similar times in different years and for those departing in the austral summer. However, while the same areas were used by individuals in different years, they were not necessarily used at the same times during the non-breeding period. Conclusions: Even in tropical systems with huge ranges of migratory routes and timings, our results suggest benefits of consistency in individual migratory behaviours. Identifying the factors that drive and maintain between-individual variation in migratory behaviour, and the consequences for breeding success and survival, will be key to understanding the consequences of environmental change across migratory ranges

Individual repeatability of avian migration phenology: A systematic review and meta-analysis

1. Changes in phenology and distribution are being widely reported for many migratory species in response to shifting environmental conditions. Understanding these changes and the situations in which they occur can be aided by understanding consistent individual differences in phenology and distribution and the situations in which consistency varies in strength or detectability. 2. Studies tracking the same individuals over consecutive years are increasingly reporting migratory timings to be a repeatable trait, suggesting that flexible individual responses to environmental conditions may contribute little to population-level changes in phenology and distribution. However, how this varies across species and sexes, across the annual cycle and in relation to study (tracking method, study design) and/or ecosystem characteristics is not yet clear. 3. Here, we take advantage of the growing number of publications in movement ecology to perform a phylogenetic multilevel meta-analysis of repeatability estimates for avian migratory timings to investigate these questions. Of 2,433 reviewed studies, 54 contained suitable information for meta-analysis, resulting in 177 effect sizes from 47 species. 4. Individual repeatability of avian migratory timings averaged 0.414 (95% confidence interval: 0.3–0.5) across landbirds, waterbirds and seabirds, suggesting consistent individual differences in migratory timings is a common feature of migratory systems. Timing of departure from the non-breeding grounds was more repeatable than timings of arrival at or departure from breeding grounds, suggesting that conditions encountered on migratory journeys and outcome of breeding attempts can influence individual variation. 5. Population-level shifts in phenology could arise through individual timings changing with environmental conditions and/or through shifts in the numbers of individuals with different timings. Our findings suggest that, in addition to identifying the conditions associated with individual variation in phenology, exploring the causes of between-individual variation will be key in predicting future rates and directions of changes in migratory timings. We therefore encourage researchers to report the within- and between- individual variance components underpinning the reported repeatability estimates to aid interpretation of migration behaviour. In addition, the lack of studies in the tropics means that levels of repeatability in less strongly seasonal environments are not yet clear

Metabarcoding, stables isotopes, and tracking: unraveling the trophic ecology of a winter-breeding storm petrel (Hydrobates castro) with a multimethod approach

Detailed information on diet and foraging ecology is scarce for most small seabirds such as storm petrels. In this study, we used molecular techniques, stable isotope analysis, and geolocators to study the diet, trophic ecology, and at-sea distribution of Madeiran storm petrels (Hydrobates castro) breeding in Farilhoes Islet, Portugal, in 2015-2017. The diet of Madeiran storm petrels was dominated by fish for both sexes and study years, with Gadidae representing the main prey family. In 2017, females also fed on Aulopiformes, Stomiiformes and Myctophiformes, which were not identified in the other groups, suggesting some degree of inter-annual and intersexual plasticity in their diet. The carbon isotopic ratios of birds during 2017 were significantly higher when compared to 2015, which might be related to foraging near coastal areas in 2017. Indeed, tracking data for 2017 show that birds foraged near the colony and near the West African coast. Overall, both sexes of this species exhibited a similar trophic ecology and diet during the breeding season. However, intersexual differences occurred during the non-breeding season, when females showed significantly lower nitrogen isotopic ratios than males (in 2016), and the lowest niche overlap between sexes occurred. This, together with the fact that environmental conditions appeared less favourable in 2016 suggests that intersexual differences in the foraging ecology of this species may be related with environmental conditions

Individual consistency in migration strategies of a tropical seabird, the Round Island petrel

Background: In migratory species, the extent of within- and between-individual variation in migratory strategies can influence potential rates and directions of responses to environmental changes. Quantifying this variation requires tracking of many individuals on repeated migratory journeys. At temperate and higher latitudes, low levels of within-individual variation in migratory behaviours are common and may reflect repeated use of predictable resources in these seasonally-structured environments. However, variation in migratory behaviours in the tropics, where seasonal predictability of food resources can be weaker, remains largely unknown. Methods: Round Island petrels (Pterodroma sp.) are tropical, pelagic seabirds that breed all year round and perform long-distance migrations. Using multi-year geolocator tracking data from 62 individuals between 2009 and 2018, we quantify levels of within- and between-individual variation in non-breeding distributions and timings. Results: We found striking levels of between-individual variation in at-sea movements and timings, with non-breeding migrations to different areas occurring across much of the Indian Ocean and throughout the whole year. Despite this, repeat-tracking of individual petrels revealed remarkably high levels of spatial and temporal consistency in within-individual migratory behaviour, particularly for petrels that departed at similar times in different years and for those departing in the austral summer. However, while the same areas were used by individuals in different years, they were not necessarily used at the same times during the non-breeding period. Conclusions: Even in tropical systems with huge ranges of migratory routes and timings, our results suggest benefits of consistency in individual migratory behaviours. Identifying the factors that drive and maintain between-individual variation in migratory behaviour, and the consequences for breeding success and survival, will be key to understanding the consequences of environmental change across migratory ranges