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Olivier Gimenez, Christophe Barbraud. (2017). Dealing with many correlated covariates in capture–recapture models (Vol. 59).
Abstract: Capture–recapture models for estimating demographic parameters allow covariates to be incorporated to better understand population dynamics. However, high-dimensionality and multicollinearity can hamper estimation and inference. Principal component analysis is incorporated within capture–recapture models and used to reduce the number of predictors into uncorrelated synthetic new variables. Principal components are selected by sequentially assessing their statistical significance. We provide an example on seabird survival to illustrate our approach. Our method requires standard statistical tools, which permits an efficient and easy implementation using standard software.
Keywords: Animal demography Population dynamics Principal-component capture–recapture model Snow petrel Survival estimation
Programme: 109
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Nathan Pacoureau, Matthieu Authier, Karine Delord, Christophe Guinet, Christophe Barbraud. (2017). Early-life density-dependence effects on growth and survival in subantarctic fur seals (Vol. 59).
Abstract: Understanding the regulation of natural populations has been a long-standing research program in ecology. Current knowledge on marine mammals and seabirds is biased toward the adult component of populations and lacking are studies investigating the juvenile component. Our goal was to estimate demographic parameters on the pre-weaning stage of a subantarctic fur seal (Arctocephalus tropicalis) population on Amsterdam Island, suspected to be regulated by density-dependence. The influence of abundance on growth parameters (length and weight) and survival was assessed over a study period spanning 16 years. We evidenced a negative trend in population growth rate when density increased. Density-dependence models were favored for pup body size and mass growth. Abundance had a clear influence on body length at high population-density, pups grew slower and were smaller at weaning than pups born in years with low population density. Abundance partly explained pup body mass variation and a weak effect was detected on pre-weaning survival. The causal mechanisms may be increased competition for food resources between breeding females, leading to a reduction of maternal input to their pups. Our results suggested that pup favored survival over growth and the development of their diving abilities in order to withstand the extreme fasting periods that are characteristic of this fur seal population. This analysis provides significant insight of density-dependent processes on early-life demographic parameters of a long lived and top-predator species, and more specifically on the pre-weaning stage with important consequences for our understanding of individual long-term fitness and population dynamics.
Keywords: Arctocephalus tropicalis Capture-mark-recapture Growth model Marine top predator Population dynamics State space model
Programme: 109
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Nathan Pacoureau, Matthieu Authier, Karine Delord, Christophe Guinet, Christophe Barbraud. (2017). Early-life density-dependence effects on growth and survival in subantarctic fur seals (Vol. 59).
Abstract: Understanding the regulation of natural populations has been a long-standing research program in ecology. Current knowledge on marine mammals and seabirds is biased toward the adult component of populations and lacking are studies investigating the juvenile component. Our goal was to estimate demographic parameters on the pre-weaning stage of a subantarctic fur seal (Arctocephalus tropicalis) population on Amsterdam Island, suspected to be regulated by density-dependence. The influence of abundance on growth parameters (length and weight) and survival was assessed over a study period spanning 16 years. We evidenced a negative trend in population growth rate when density increased. Density-dependence models were favored for pup body size and mass growth. Abundance had a clear influence on body length at high population-density, pups grew slower and were smaller at weaning than pups born in years with low population density. Abundance partly explained pup body mass variation and a weak effect was detected on pre-weaning survival. The causal mechanisms may be increased competition for food resources between breeding females, leading to a reduction of maternal input to their pups. Our results suggested that pup favored survival over growth and the development of their diving abilities in order to withstand the extreme fasting periods that are characteristic of this fur seal population. This analysis provides significant insight of density-dependent processes on early-life demographic parameters of a long lived and top-predator species, and more specifically on the pre-weaning stage with important consequences for our understanding of individual long-term fitness and population dynamics.
Programme: 109
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Samara Danel, Nancy Rebout, Francesco Bonadonna, Dora Biro. (2022). Wild skuas can use acoustic cues to locate hidden food.
Abstract: Among animals, the visual acuity of several predatory bird species is probably the most outstanding. This, and the ease with which visually based tasks are administered, has led researchers to predominantly use the visual modality when studying avian cognition. Some wild skua populations routinely use acoustic cues emitted by their prey during foraging. In this study, we thus assessed whether this species was able to locate hidden food using acoustic cues alone (training phase). During the subsequent test phase, we investigated the capacity of successful individuals to choose the correct baited container in four conditions: (i) baited (shaking the baited container), (ii) full information (shaking both containers), (iii) exclusion (shaking the empty container), and (iv) control (shaking neither container). Four out of ten subjects succeeded in locating the baited container in the training phase. During the test phase, most subjects chose the baited container significantly more than the empty container in the baited and full information condition, while their performance was at chance level in the control condition. When no sound emanated from the empty container in the exclusion condition, one out of four skuas chose the baited container with more accuracy than predicted by chance. As this bird chose correctly on the first trial and during the first five trials, its performance is unlikely due to learning processes (learning to exclude the empty container). Although further tests are necessary to draw firm conclusions, our results open the way for assessing further this species’ reasoning abilities in the wild.
Keywords: Acoustic cue Cups task Exclusion performance Inferential reasoning by exclusion Shaking
Programme: 354
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C. Barbraud, J. Vasseur, K. Delord. (2018). Using distance sampling and occupancy rate to estimate abundance of breeding pairs of Wilson’s Storm Petrel (Oceanites oceanicus) in Antarctica (Vol. 41).
Abstract: Reliable population estimates are needed for the conservation management of seabird populations. Failing to account for detection probability in surveys often leads to underestimate population size and, if detection probability varies among surveys, to bias the estimated trends. This is particularly relevant for storm petrels, which are widespread small burrow- or cavity-nesting seabirds, which have low detection probabilities on land and at sea and whose population status and trends are the least known among seabirds. Here, we used the distance sampling method to estimate detection probability and breeding population size of the cavity-nesting Wilson’s Storm Petrel (Oceanites oceanicus) in the Pointe Géologie archipelago, East Antarctica. Detection probability was 0.353 ± 0.053 and the average density of active nests was 45.53 ± 15.63 nests/ha. The proportion of nests occupied by breeders was estimated using an endoscope on a sample of nests and was 0.455 ± 0.053. The breeding population was estimated to be 793 (95% CI 344–1359) breeding pairs in January 2016. We advocate the distance sampling method as a robust approach to estimate abundance of breeding Wilson’s Storm Petrels in Antarctica. Comparison with an earlier survey suggests that the population has decreased over the past 30 years, possibly partly due to a reduction in nesting habitat following the extension of the surface area occupied by penguin colonies.
Keywords: Breeding population Storm petrel Terre Adélie
Programme: 109
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Caio V. Z. Cipro, Y. Cherel, P. Bocher, F. Caurant, P. Miramand, P. Bustamante. (2018). Trace elements in invertebrates and fish from Kerguelen waters, southern Indian Ocean (Vol. 41).
Abstract: Given the lack of background data on essential and non-essential trace elements in invertebrates and fish known to be the predominant prey of marine mammals and seabirds breeding at the Kerguelen Islands, this study intends to provide these results of great influence for predators in higher trophic levels. To this end, plankton organisms (9 species/4 phyla), mollusks (2 bivalves and 2 squid species) and fishes (8 benthic and 10 pelagic species) from Kerguelen waters were analysed for cadmium (Cd), copper (Cu), mercury (Hg) and zinc (Zn). Individual concentrations of non-essential elements (particularly Cd) showed larger variation in comparison with essential ones likely due to their homeostasis. Thus Cd ranged over 4 orders of magnitude; however, Hg ranged only 1, without significant correlation to trophic level. Instead, ecological parameters (benthic/mesopelagic habitat and feeding ecology) showed a more important influence on the results. Concerning seashore organisms, bivalves collected inside the Gulf of Morbihan had higher Cd concentrations compared to those from the Kerguelen shelf, suggesting a local source of Cd, such as runoff water from bird colonies. Comparison with the literature showed metal concentrations in invertebrates and fishes from Kerguelen Islands somewhat lower than those in the Antarctic area, with Hg prevailing in benthic species and Cd in pelagic ones. In contrast to Hg, Cd values of squids, jellyfish and the amphipod Themisto gaudichaudii were significantly higher than all other species. Finally, top predators foraging in this area that can be subject to potentially high Hg and Cd exposure through their diet at Kerguelen are reviewed.
Keywords: Food web Kerguelen Metals Myctophid Plankton Trace elements
Programme: 109
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Karine Delord, Yves Cherel, Christophe Barbraud, Olivier Chastel, Henri Weimerskirch. (2018). High variability in migration and wintering strategies of brown skuas (Catharacta antarctica lonnbergi) in the Indian Ocean (Vol. 41).
Abstract: Movements of brown skuas (Catharacta antarctica lonnbergi) originating from two populations in the southern Indian Ocean were studied during the nonbreeding period using geolocation. A total of 33 individuals were equipped resulting in 34 annual tracks recovered from 50 deployments. Brown skuas varied extensively in their post-breeding movements, from true long range migrations to reach distant wintering zones, to short movements in the vicinity of breeding grounds. Overall, brown skuas migrated northward to overwinter in different areas in the southern hemisphere; individuals remained in the Indian Ocean, except two that overwintered in the Benguela Current (Atlantic Ocean). Wintering grounds were generally situated in productive dynamic upwelling waters or frontal systems. Brown skuas avoided the less productive area of the South Subtropical Gyre in the Central Indian Ocean. Individuals clearly differed in migratory strategies, targeting areas in a continuum from the sub-Antarctic to the tropics. Inter-individual differences were not sex-dependent. The migration dates varied between sexes with females leaving the breeding sites earlier and returning later compared to males. The duration of migration depended on wintering area and sex. Males had shorter migrations than females, regardless of the wintering area. Isotopic signatures clearly indicated that birds moulted in the wintering area and during migration. The low δ 15N values of feathers that grew in mixed subtropical-sub-Antarctic waters suggest that skuas fed on low trophic level prey in these areas. The origin and consequences of such strong inter-individual variation in migratory strategies requires further investigation.
Keywords: Activity Feather Geolocator Intraspecific strategies Phenology Stable isotopes
Programme: 109
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Henri Weimerskirch, Aurélien Prudor, Quentin Schull. (2018). Flights of drones over sub-Antarctic seabirds show species- and status-specific behavioural and physiological responses (Vol. 41).
Abstract: Drones and unmanned aerial vehicles are increasingly used in research on wildlife. Their wide applications can also give interesting insights into habitat use and population distribution. However, the disturbance they might be responsible for, on species and especially in protected areas has yet to be investigated. We assessed and compared the behavioural response of 11 southern seabird species at the Crozet Islands, Southern Indian Ocean, to drone approaches at specific altitudes. We first show that the behavioural response differed between species depending on the altitude of the drone approach. At 50 m of altitude, only one of the studied species showed a detectable reaction, whereas at 10 m, most species showed strong behavioural postures of stress. Adult penguins breeding in large colonies, and some albatross species showed little behavioural response even when the drone was as close as 3 m, whereas other species such as giant petrels or cormorants appeared highly sensitive to drone approaches. Among King Penguins, although incubating adults showed little signs of behavioural stress, non-breeding adults and fledglings in crèches exhibited strong behavioural responses to the drone approach. Monitoring heart rate allowed us to investigate the link between behavioural and physiological response to that specific potential stressor in king penguins. Whereas we confirmed the expected link between physiological and behavioural response in chicks, breeding adults showed no behavioural sign of stress but had a significant increase in heart rate, the relative increase being higher than in chicks. All together these results have important implications for the conservation of species and should be helpful for future legislations on the use of drones.
Keywords: Albatrosses Altitude Disturbance Penguins Petrels UAV
Programme: 109
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Laurie Thiers, Karine Delord, Charles-André Bost, Christophe Guinet, Henri Weimerskirch. (2017). Important marine sectors for the top predator community around Kerguelen Archipelago (Vol. 40).
Abstract: The French Kerguelen Archipelago represents an important breeding place for many species of marine top predators within the Southern Ocean, making the plateau hosting the archipelago and surrounding waters (CCAMLR area 58.5) a crucial area to design conservation measures. In this study, available tracking data from nine species of seabirds and marine mammals breeding at Kerguelen were analysed to define potential boundaries for a Marine Protected Area. Maps of time spent per square of each species were first used to describe high-use areas within the Kerguelen Plateau. Habitat models were then developed for four species (Black-browed albatross, Wandering albatross, King penguin and Antarctic fur seal) chosen on the basis of their contrasted foraging ecology and diet to represent the top predator community. Predictive models were then applied to the main colonies of the four species for which no tracking data were available to illustrate the most important feeding areas at the scale of the entire study zone. An area delineated by the central part of the plateau and its slopes appeared to be of great importance for the top predators’ community and would appropriately complete the limits of the existing Australian marine reserve of Heard and McDonald Islands.
Keywords: Distribution Habitat modelling Marine mammals Seabirds Tracking
Programme: 109
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Henri Weimerskirch, Karine Delord, Christophe Barbraud, Fabrice Le Bouard, Peter G. Ryan, Peter Fretwell, Cédric Marteau. (2018). Status and trends of albatrosses in the French Southern Territories, Western Indian Ocean (Vol. 41).
Abstract: Today albatrosses are threatened worldwide, especially by fishing activities, and many populations are currently in decline. Albatrosses breeding at the French Southern Territories in the south-western Indian Ocean, on the Crozet, Kerguelen and Saint-Paul–Amsterdam island archipelagos, are monitored regularly. This monitoring has been based on a sample of species and sites, and there was a need for an assessment of the population trends for all species at each site. During the past 3 years most populations have been surveyed, allowing an assessment of the trends of albatrosses breeding at the archipelagos of the French Southern Territories over the past 40 years. Wandering Albatrosses show similar trends at all sites within the Crozet and Kerguelen archipelagos, with a recent recovery of colonies after strong declines in the 1970s. Amsterdam Albatrosses are increasing, albeit at lower rates during recent years. Indian Yellow-nosed Albatrosses show a global decline over the entire range. The trends among Black-browed and Grey-headed Albatrosses vary between colonies and archipelagos. Sooty Albatrosses have continuously decreased in numbers whereas Light-mantled Albatross numbers vary considerably between years, with an overall increase over the past 30 years. These results confirm that the French Southern Territories in the south-west Indian Ocean support a significant portion of the world populations of several albatross species. Several species appear to be steadily decreasing probably because of the impact of fisheries and disease outbreaks. The reasons for different trends among populations of the same species are not well understood and require further investigation.
Keywords: Amsterdam Crozet Fisheries Kerguelen Monitoring
Programme: 109
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