Mark–recapture surveys are commonly used to monitor translocated populations globally. Data gathered are then used to estimate demographic parameters, such as abundance and survival, using ...Jolly–Seber (JS) models. However, in translocated populations initial population size is known and failure to account for this may bias parameter estimates, which are important for informing conservation decisions during population establishment. Here, we provide methods to account for known initial population size in JS models by incorporating a separate component likelihood for translocated individuals, using a maximum‐likelihood estimation, with models that can be fitted using either R or MATLAB. We use simulated data and a case study of a threatened lizard species with low capture probability to demonstrate that unconstrained JS models may overestimate the size of translocated populations, especially in the early stages of post‐release monitoring. Our approach corrects this bias; we use our simulations to demonstrate that overestimates of population size between 78% and 130% can occur in the unconstrained JS models when the detection probability is below 0.3 compared to 1%–8.9% for our constrained model. Our case study did not show an overestimate; however accounting for the initial population size greatly reduced error in all parameter estimates and prevented boundary estimates. Adopting the corrected JS model for translocations will help managers to obtain more robust estimates of the population sizes of translocated animals, better informing future management including reinforcement decisions, and ultimately improving translocation success.
Storms can cause widespread seabird stranding and wrecking,1,2,3,4,5 yet little is known about the maximum wind speeds that birds are able to tolerate or the conditions they avoid. We analyzed ...>300,000 h of tracking data from 18 seabird species, including flapping and soaring fliers, to assess how flight morphology affects wind selectivity, both at fine scales (hourly movement steps) and across the breeding season. We found no general preference or avoidance of particular wind speeds within foraging tracks. This suggests seabird flight morphology is adapted to a “wind niche,” with higher wing loading being selected in windier environments. In support of this, wing loading was positively related to the median wind speeds on the breeding grounds, as well as the maximum wind speeds in which birds flew. Yet globally, the highest wind speeds occur in the tropics (in association with tropical cyclones) where birds are morphologically adapted to low median wind speeds. Tropical species must therefore show behavioral responses to extreme winds, including long-range avoidance of wind speeds that can be twice their operable maxima. By contrast, Procellariiformes flew in almost all wind speeds they encountered at a seasonal scale. Despite this, we describe a small number of cases where albatrosses avoided strong winds at close range, including by flying into the eye of the storm. Extreme winds appear to pose context-dependent risks to seabirds, and more information is needed on the factors that determine the hierarchy of risk, given the impact of global change on storm intensity.6,7
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•Maximum wind speed selected by seabirds during foraging trips related to morphology•Flight morphology is adapted to the long-term median, not maximum, wind speeds•Tropical species are adapted to low wind speeds but experience the strongest storms•The most wind-adapted species flew into the eye of storms to avoid unfavorable winds
Using >300,000 h of tracking data from 18 seabird species, Nourani et al. show seabirds’ adaptation to a wind niche determined by long-term median, not maximum, wind speeds. The selection pressure for behavioral responses to extreme winds should be strongest in the tropics, but even the most wind-adapted species sometimes avoid extreme winds.
We report the concentrations of persistent organic pollutants (POPs) in seabird eggs from St. Brandon's Atoll, a tropical island system in the western Indian Ocean. Ten eggs each of sooty terns ...(Onychoprion fuscatus), fairy terns (Gygis alba), and common noddies (Anous stolidus) were collected from the atoll. For a terrestrial reference, we analysed three feral chicken (Gallus gallus domesticus) eggs from the same location. Sooty tern eggs contained the highest mean concentrations of three chemical classes: ƩCHL3 (0.21 ng/g wm; wet mass), ƩPCB10 (1.5 ng/g wm), and ƩPBDE6 (1.1 ng/g wm). Fairy tern eggs contained the highest mean concentrations of HCB (0.68 ng/g wm) and ƩCHB5 (0.83 ng/g wm). The chicken eggs contained the highest mean concentrations of ƩDDT3 (2.6 ng/g wm), while common noddy eggs contained the highest mean concentrations of ƩHCH2 (0.5 ng/g wm). We surmise that the differences in chemical composition between species reflect different pollutant compositions in prey from the bird's different foraging ranges. The sooty terns foraging offshore contained higher POPs concentrations than the nearshore-foraging common noddies. Fairy tern eggs contained intermediate concentrations, commensurate with their intermediate foraging. Inter-island differences in contaminant concentrations were seen between eggs of the common noddies from St. Brandon's Atoll and Rodrigues Island, 520 km to the south-east. Concentrations of contaminants found in this study were lower than values quantified by other studies, making St. Brandon's Atoll an ideal reference site to monitor background concentrations of POPs in the tropical Indian Ocean.
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•This is the first study to quantify POPs in birds' eggs from St. Brandon's Atoll in 45 years.•Current DDT concentrations are lower than in 1975.•Mean POPs concentrations were lower than concentrations found in similar studies.•The highest concentrations of POPs were found in sooty tern eggs.•POPs were quantified in terrestrial birds (chickens) from the atoll for the first time.
The invasion of the giant Madagascar day gecko Phelsuma grandis has increased the threats to the four endemic Mauritian day geckos (Phelsuma spp.) that have survived on mainland Mauritius. We had two ...main aims: (i) to predict the spatial distribution and overlap of P. grandis and the endemic geckos at a landscape level; and (ii) to investigate the effects of P. grandis 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 P. grandis 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 P. grandis. The predicted range of each species varied from 85 km2 to 376 km2. Sixty percent of the predicted range of P. grandis overlapped with the combined predicted ranges of the four endemic geckos; 15% of the combined predicted ranges of the four endemic geckos overlapped with P. grandis. Levin's niche breadth varied from 0.140 to 0.652 between P. grandis and the four endemic geckos. The abundance of endemic geckos was 89% lower in sites with P. grandis compared to sites without P. grandis, and the endemic geckos had been extirpated at four of ten sites we surveyed with P. grandis. Species Distribution Modelling, together with the breadth metrics, predicted that P. grandis 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 P. grandis. This is a cause of concern in both Mauritius and other countries with endemic species of Phelsuma.
Body-mounted accelerometers provide a new prospect for estimating power use in flying birds, as the signal varies with the two major kinematic determinants of aerodynamic power: wingbeat frequency ...and amplitude. Yet wingbeat frequency is sometimes used as a proxy for power output in isolation. There is, therefore, a need to understand which kinematic parameter birds vary and whether this is predicted by flight mode (e.g. accelerating, ascending/descending flight), speed or morphology. We investigate this using high-frequency acceleration data from (i) 14 species flying in the wild, (ii) two species flying in controlled conditions in a wind tunnel and (iii) a review of experimental and field studies. While wingbeat frequency and amplitude were positively correlated,
R
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values were generally low, supporting the idea that parameters can vary independently. Indeed, birds were more likely to modulate wingbeat amplitude for more energy-demanding flight modes, including climbing and take-off. Nonetheless, the striking variability, even within species and flight types, highlights the complexity of describing the kinematic relationships, which appear sensitive to both the biological and physical context. Notwithstanding this, acceleration metrics that incorporate both kinematic parameters should be more robust proxies for power than wingbeat frequency alone.
The use of ecological replacements (analogue species to replace extinct taxa) to restore ecosystem functioning is a promising conservation tool. However, this approach is controversial, in part due ...to a paucity of data on interactions between analogue species and established taxa in the ecosystem.
We conducted ecological surveys, comprehensively DNA barcoded an ecosystem's flora and inferred the diet of the introduced Aldabra giant tortoise, acting as an ecological replacement, to understand how it might have modified island plant communities on a Mauritian islet. Through further dietary analyses, we investigated consequential effects on the threatened endemic Telfair's skink.
Dietary overlap between tortoises and skinks was greater than expected by chance. However, there was a negative correlation between tortoise and skink preferences in herbivory and minimal overlap in the plants most frequently consumed by the reptiles.
Changes in the plant community associated with 7 years of tortoise grazing were characterised by a decrease in the percentage cover of native herbs and creepers, and an increase in the cover of an invasive herb when compared to areas without tortoises. However, tortoise dietary preferences themselves did not directly drive changes in the plant community.
Tortoises successfully dispersed the seeds of an endemic palm, which in time may increase the extent of unique palm‐rich habitat. We found no evidence that tortoises have increased the extent of plant species hypothesised to be part of a lost Mauritian tortoise grazed community.
Synthesis and applications. Due to a negative correlation in tortoise and skink dietary preferences and minimal overlap in the most frequently consumed taxa, the presence of tortoises is unlikely to have detrimental impacts on Telfair's skinks. Tortoise presence is likely to be beneficial to skinks in the long term by increasing the extent of palm‐rich habitat. Although tortoises are likely to play a role in controlling invasive plants, they are not a panacea for this challenge. After 7 years, tortoises have not resurrected a lost tortoise grazed community that we hypothesise might have existed in limited areas on the islet, indicating that further interventions may be required to restore this plant community.
Résumé
L'utilisation de remplacements écologiques (espèces analogues pour remplacer les taxons éteints) pour restaurer le fonctionnement d'un écosystème est un outil de conservation prometteur. Cependant, cette approche est controversée, en partie à cause d'un manque de données sur les interactions entre les espèces analogues et les taxons présents dans l'écosystème.
Nous avons mené des études écologiques, codé l’ADN de la flore d'un écosystème et déduit le régime alimentaire de la tortue géante d'Aldabra, espèce introduite agissant comme un remplacement écologique, pour comprendre comment elle aurait potentiellement modifié les communautés végétales insulaires sur un îlot mauricien. Grâce à d'autres analyses alimentaires, nous avons étudié les effets résultants sur le scinque de Telfair, une espèce endémique menacée.
Le chevauchement entre l'alimentation des tortues et les scinques était plus important que prévu. Cependant, il y avait une corrélation négative entre les préférences des tortues et des scinques au niveau de l'herbivorie et un chevauchement minime pour les plantes les plus fréquemment consommées par ces reptiles.
Les changements dans la communauté végétale associés à sept années de broutage des tortues ont été caractérisés par une diminution du pourcentage de couverture d'herbes et de plantes grimpantes indigènes, et une augmentation de la couverture d'une herbe envahissante par rapport aux zones sans tortues. Cependant, les préférences alimentaires des tortues elles‐mêmes n'ont pas directement entraîné de changements dans la communauté végétale.
Les tortues ont réussi à disperser les graines d'un palmier endémique, ce qui, avec le temps, pourrait augmenter l'étendue de l'habitat riche en palmiers. Nous n'avons trouvé aucune preuve que les tortues ont augmenté l'étendue des espèces végétales supposées faire partie d'une communauté végétale disparue qui existait dû au broutage des tortues mauriciennes.
Synthèse et applications. En raison d'une corrélation négative dans les préférences alimentaires des tortues et des scinques et d'un chevauchement minimal dans les taxons les plus fréquemment consommés, il est peu probable que la présence de tortues ait des effets néfastes sur les scinques de Telfair. La présence de tortues est susceptible d'être bénéfique pour les scinques à long terme en augmentant l'étendue de l'habitat riche en palmiers. Bien que les tortues soient susceptibles de jouer un rôle dans le contrôle des plantes envahissantes, elles ne sont pas une panacée pour ce défi. Après sept ans, les tortues n'ont pas ressuscité la communauté végétale disparue qui existait dû au broutage des tortues endémique qui, selon nous, aurait pu exister dans des zones limitées de l'îlot, ce qui indique que d'autres interventions pourraient être nécessaires pour restaurer cette communauté végétale.
Due to a negative correlation in tortoise and skink dietary preferences and minimal overlap in the most frequently consumed taxa, the presence of tortoises is unlikely to have detrimental impacts on Telfair's skinks. Tortoise presence is likely to be beneficial to skinks in the long term by increasing the extent of palm‐rich habitat. Although tortoises are likely to play a role in controlling invasive plants, they are not a panacea for this challenge. After 7 years, tortoises have not resurrected a lost tortoise grazed community that we hypothesise might have existed in limited areas on the islet, indicating that further interventions may be required to restore this plant community.
Per- and polyfluoroalkyl substances (PFAS) are anthropogenic fluorinated compounds of concern for human and environmental health. There is no data on PFAS concentrations in marine bird eggs from the ...Western Indian Ocean. We analysed eight PFAS in eggs of fairy terns (Gygis alba), sooty terns (Onychoprion fuscatus), and common noddies (Anous stolidus) from St. Brandon's Atoll. Fairy tern eggs contained the highest concentrations, followed by sooty terns and common noddies. Perfluoroundecanoic acid (PFUdA) had the highest mean concentration (2.3 ng/g wm), followed by perfluorooctane sulfonic acid (PFOS) (2.0 ng/g wm), and perfluorononanoic acid (PFNA) (0.93 ng/g wm) in fairy tern eggs. Concentrations of all PFAS were lower than values found in literature. PFOS and PFOA concentrations were three orders of magnitude lower than toxicity reference values and levels of lowest-observed-adverse-effect-level concentrations. Eggs from St. Brandon's would be useful to monitor background changes on a regional and perhaps global scale.
•First study on PFAS in the eggs of seabirds from the Western Indian Ocean•PFAS were compared with eggs of terrestrial birds from the same atoll.•The highest PFAS concentrations were found in fairy tern eggs.•The detected PFAS concentrations were lower than other studies.•PFOS and long chained PFCAs of odd-numbered chain lengths were the most prominent PFAS.
Introduced species can exert disproportionately negative effects on island ecosystems, but their potential role as food for native consumers is poorly studied. Telfair's skinks are endemic omnivores ...living on Round Island, Mauritius, a globally significant site of biodiversity conservation. We aimed to determine the dietary diversity and key trophic interactions of Telfair's skinks, whether introduced species are frequently consumed, and if diet composition changes seasonally between male and female skinks. We used DNA metabarcoding of skink fecal samples to identify animals (COI) and plants (ITS2) consumed by skinks. There were 389 dietary presence counts belonging to 77 dietary taxa found across the 73 Telfair's skink fecal samples. Introduced taxa were cumulatively consumed more frequently than other categories, accounting for 49.4% of all detections, compared to cryptogenic (20.6%), native (20.6%), and endemic taxa (9.5%). The most frequently consumed introduced species was the ant, Pheidole megacephala, present in 40% of samples. Blue latan palm, Latania loddigesii, was the most frequently consumed endemic species, present in 33% of samples but was only detected in the dry season, when fruits are produced. We found a strong seasonal difference in diet composition explained by the presence of certain plant species solely or primarily in one season and a marked increase in the consumption of animal prey in the dry season. Male and female skinks consumed several taxa at different frequencies. These results present a valuable perspective on the role of introduced species in the trophic network of their invaded ecosystem. Both native and introduced species provide nutritional resources for skinks, and this may have management implications in the context of species conservation and island restoration.
Telfair's skinks are keystone omnivores found on Round Island, Mauritius. Using a multimarker DNA metabarcoding approach, we identify that this endemic species frequently consumes introduced species, which comprise almost 50% of all prey detections. This provides a valuable insight into how introduced species may fit into the food web in their introduced range.
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 have collated a long‐term mark–recapture dataset in conjunction with a 10‐year GLS tagging programme and examined 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 (95% CI 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.
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