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

Widespread gene flow between oceans in a pelagic seabird species complex

Global-scale gene flow is an important concern in conservation biology as it has the potential to either increase or decrease genetic diversity in species and populations. Although many studies focus on the gene flow between different populations of a single species, the potential for gene flow and introgression between species is understudied, particularly in seabirds. The only well studied example of a mixed-species, hybridising population of petrels exists on Round Island, in the Indian Ocean. Previous research assumed that Round Island represents a point of secondary contact between Atlantic (Pterodroma arminjoniana) and Pacific species (P. neglecta and P. heraldica). This study uses microsatellite genotyping and tracking data to address the possibility of between-species hybridisation occurring outside the Indian Ocean. Dispersal and gene flow spanning three oceans was demonstrated between the species in this complex. Analysis of migration rates estimated using BAYESASS revealed unidirectional movement of petrels from the Atlantic and Pacific into the Indian Ocean. Conversely, STRUCTURE analysis revealed gene-flow between species of the Atlantic and Pacific Oceans, with potential three-way hybrids occurring outside the Indian Ocean. Additionally, geolocation tracking of Round Island petrels revealed two individuals travelling to the Atlantic and Pacific. These results suggest that inter-specific hybrids in Pterodroma petrels are more common than was previously assumed. This study is the first of its kind to investigate gene flow between populations of closely related Procellariform species on a global scale, demonstrating the need for consideration of widespread migration and hybridisation in the conservation of threatened seabirds

Global assessment of marine plastic exposure risk for oceanic birds

Plastic pollution is distributed patchily around the world’s oceans. Likewise, marine organisms that are vulnerable to plastic ingestion or entanglement have uneven distributions. Understanding where wildlife encounters plastic is crucial for targeting research and mitigation. Oceanic seabirds, particularly petrels, frequently ingest plastic, are highly threatened, and cover vast distances during foraging and migration. However, the spatial overlap between petrels and plastics is poorly understood. Here we combine marine plastic density estimates with individual movement data for 7137 birds of 77 petrel species to estimate relative exposure risk. We identify high exposure risk areas in the Mediterranean and Black seas, and the northeast Pacific, northwest Pacific, South Atlantic and southwest Indian oceans. Plastic exposure risk varies greatly among species and populations, and between breeding and non-breeding seasons. Exposure risk is disproportionately high for Threatened species. Outside the Mediterranean and Black seas, exposure risk is highest in the high seas and Exclusive Economic Zones (EEZs) of the USA, Japan, and the UK. Birds generally had higher plastic exposure risk outside the EEZ of the country where they breed. We identify conservation and research priorities, and highlight that international collaboration is key to addressing the impacts of marine plastic on wide-ranging species

Global assessment of marine plastic exposure risk for oceanic birds

Plastic pollution is distributed patchily around the world’s oceans. Likewise, marine organisms that are vulnerable to plastic ingestion or entanglement have uneven distributions. Understanding where wildlife encounters plastic is crucial for targeting research and mitigation. Oceanic seabirds, particularly petrels, frequently ingest plastic, are highly threatened, and cover vast distances during foraging and migration. However, the spatial overlap between petrels and plastics is poorly understood. Here we combine marine plastic density estimates with individual movement data for 7137 birds of 77 petrel species to estimate relative exposure risk. We identify high exposure risk areas in the Mediterranean and Black seas, and the northeast Pacific, northwest Pacific, South Atlantic and southwest Indian oceans. Plastic exposure risk varies greatly among species and populations, and between breeding and non-breeding seasons. Exposure risk is disproportionately high for Threatened species. Outside the Mediterranean and Black seas, exposure risk is highest in the high seas and Exclusive Economic Zones (EEZs) of the USA, Japan, and the UK. Birds generally had higher plastic exposure risk outside the EEZ of the country where they breed. We identify conservation and research priorities, and highlight that international collaboration is key to addressing the impacts of marine plastic on wide-ranging species

No detectable effect of geolocator deployment on the short‐ or long‐term apparent survival of a tropical seabird

A wide range of biologging devices are now commonly deployed to study the movement ecology of birds, but deployment of these devices is not without its potential risks and negative impacts on the welfare, behaviour and fitness of tagged individuals. However, empirical evidence for the effects of tags is equivocal. Global location sensing (GLS) loggers are small, light level recording devices that are well suited to studying the large-scale migratory movements of many birds. However, few published studies have examined their impact on adult survival, a key demographic rate for long-lived species, such as seabirds. To address this, we collate a long-term mark-recapture data set in conjunction with a 10-year GLS tagging programme and examine the impact of tarsus-mounted GLS loggers on the adult apparent survival probabilities of a medium-sized tropical gadfly petrel. We found no evidence to indicate that deployment of GLS loggers affected apparent adult survival probabilities either in the short-term, i.e., during deployment, or in the long-term, i.e., from carrying a device at some point in the past. Annual adult apparent survival was estimated at 0.965 (CIs 0.962, 0.968) during 1993-2018. Our findings suggest that using GLS loggers to document the movements of medium-sized gadfly petrels over multiple years is a viable technique without negatively impacting adult survival. This result has potential relevance to movement ecology studies of other ecologically and morphologically similar seabirds through GLS logger deployments

No detectable effect of geolocator deployment on the short‐ or long‐term apparent survival of a tropical seabird

A wide range of biologging devices are now commonly deployed to study the movement ecology of birds, but deployment of these devices is not without its potential risks and negative impacts on the welfare, behaviour and fitness of tagged individuals. However, empirical evidence for the effects of tags is equivocal. Global location sensing (GLS) loggers are small, light level recording devices that are well suited to studying the large-scale migratory movements of many birds. However, few published studies have examined their impact on adult survival, a key demographic rate for long-lived species, such as seabirds. To address this, we collate a long-term mark-recapture data set in conjunction with a 10-year GLS tagging programme and examine the impact of tarsus-mounted GLS loggers on the adult apparent survival probabilities of a medium-sized tropical gadfly petrel. We found no evidence to indicate that deployment of GLS loggers affected apparent adult survival probabilities either in the short-term, i.e., during deployment, or in the long-term, i.e., from carrying a device at some point in the past. Annual adult apparent survival was estimated at 0.965 (CIs 0.962, 0.968) during 1993-2018. Our findings suggest that using GLS loggers to document the movements of medium-sized gadfly petrels over multiple years is a viable technique without negatively impacting adult survival. This result has potential relevance to movement ecology studies of other ecologically and morphologically similar seabirds through GLS logger deployments

Contrasting recovery trajectories of four reintroduced populations of the Endangered Mauritius Kestrel ( Falco punctatus )

Conservation translocations are commonly used in recovery programmes for threatened species from a wide range of taxa but outcomes can vary considerably both within and between programmes, and the causes of success or failure are often unclear. Central to understanding translocation success is the implementation of an accompanying monitoring programme, enabling the drivers of population establishment and persistence to be explored within a population ecology framework. Here we review and assess the outcome of a translocation programme for the Endangered Mauritius Kestrel, which involved the initial translocation of captive-reared Kestrels into four isolated populations and long-term nest-site management and monitoring. We show that after 20 years these four populations have different recovery trajectories including local extinction, recent decline and comparative stability. We explore the demographic drivers behind these trajectories and how they have been influenced, and could potentially be manipulated, by conservation management actions. Metrics of breeding performance differed between populations and in part this was driven by nest-site selection, with Kestrels nesting more frequently, laying larger clutch sizes and rearing larger broods in nestboxes. We found no compelling evidence for inter-population variation in survival rates. Simulating population trajectories under a range of conservation management scenarios, including further conservation translocations or a scaling up of nest-site management, suggested that the latter would be a more effective, practical long-term solution for the population currently in decline. Our findings provide valuable insights into the merits of monitoring, population demographic reviews and the challenges associated with identifying and mitigation for the drivers of rarity in threatened species

Ecological Effects of the Invasive Giant Madagascar Day Gecko on Endemic Mauritian Geckos: Applications of Binomial-Mixture and Species Distribution Models

<div><p>The invasion of the giant Madagascar day gecko <i>Phelsuma grandis</i> has increased the threats to the four endemic Mauritian day geckos (<i>Phelsuma</i> spp.) that have survived on mainland Mauritius. We had two main aims: (i) to predict the spatial distribution and overlap of <i>P. grandis</i> and the endemic geckos at a landscape level; and (ii) to investigate the effects of <i>P. grandis</i> on the abundance and risks of extinction of the endemic geckos at a local scale. An ensemble forecasting approach was used to predict the spatial distribution and overlap of <i>P. grandis</i> and the endemic geckos. We used hierarchical binomial mixture models and repeated visual estimate surveys to calculate the abundance of the endemic geckos in sites with and without <i>P. grandis</i>. The predicted range of each species varied from 85 km² to 376 km². Sixty percent of the predicted range of <i>P. grandis</i> overlapped with the combined predicted ranges of the four endemic geckos; 15% of the combined predicted ranges of the four endemic geckos overlapped with <i>P. grandis</i>. Levin's niche breadth varied from 0.140 to 0.652 between <i>P. grandis</i> and the four endemic geckos. The abundance of endemic geckos was 89% lower in sites with <i>P. grandis</i> compared to sites without <i>P. grandis</i>, and the endemic geckos had been extirpated at four of ten sites we surveyed with <i>P. grandis</i>. Species Distribution Modelling, together with the breadth metrics, predicted that <i>P. grandis</i> can partly share the equivalent niche with endemic species and survive in a range of environmental conditions. We provide strong evidence that smaller endemic geckos are unlikely to survive in sympatry with <i>P. grandis</i>. This is a cause of concern in both Mauritius and other countries with endemic species of <i>Phelsuma</i>.</p></div

The mean endemic gecko abundance (with 95% confidence intervals) in sites with and without <i>Phelsuma grandis</i>.

<p>Sites without <i>Phelsuma grandis</i> had a high abundance of endemic geckos, those with <i>Phelsuma grandis</i> a low abundance of endemic geckos. N = 10 sites with <i>Phelsuma grandis</i>, N = 11 sites without <i>Phelsuma grandis</i>.</p

The binary projection and overlap between <i>Phelsuma grandis</i> and four endemic species of <i>Phelsuma</i>.

<p>Each map shows the overlap of <i>P. grandis</i> and one of the endemic species. On each map, grey indicates that no species of <i>Phelsuma</i> were predicted to be present, yellow shows the predicted range of <i>Phelsuma grandis</i>, blue the predicted range of that species of endemic <i>Phelsuma</i>, and red areas of predicted overlap between the two species. The first number in each heading is the % overlap of the predicted range of <i>Phelsuma grandis</i> with that species of endemic gecko and the second number is the % overlap of the endemic species' predicted range with that of <i>Phelsuma grandis</i>. The different maps suggest that <i>Phelsuma cepediana</i> (a) and <i>Phelsuma ornata</i> (c) will overlap more with <i>Phelsuma grandis</i> and thus could be at greater risk.</p