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Les articles de David Vallecillo
de David Vallecillo, Matthieu Guillemain, Colin Bouchard, Sébastien Roques, Jocelyn Champagnon
In Biodiversity and conservation, 32 (Septembre, 2023), 23
En ligne : link.springer.com[...]
Explaining changes in waterfowl distribution and abundance is requested by wetland managers for a better understanding of their population dynamics and habitat use. The objective of this study was to assess the influence of interannual changes in wetland management, both through direct data and proxies, on the distribution dynamics of Teal day-roosts in the Camargue, a large wetland complex in southern France. We constructed a statespace model accounting for a conditional detection probability by aerial observers during duck counts, since changes in observers have a strong influence on variations in detection probability. First, we showed that the distribution of Teal day-roosts within the Camargue delta has changed over the last 35 years. Second, on a sub-sample of 18 years, we showed that annual changes in Teal abundance depended on salinity and open water area at the day-roost, and on the availability of potential feeding grounds surrounding the day-roost (available wetland area within 5 km). No association was detected between changes in Teal abundance and changes in the typology of wetland hydrology, or with changes in site protection status (i.e. hunted to protected). Our results reinforce the importance of considering management at the scale of functional units, by considering the complementarity of nocturnal feeding areas (mainly hunted areas) specifically managed for waterfowl, and diurnal roosts (mainly nature reserves, which have high conservation value for other animal and plant species). A good understanding of the factors affecting the localisation of waterfowl day-roosts is becoming more important in the context of climate change, which is likely to redistribute local birds with rising sea levels and increasing salinity in wetlands.Evaluation of the distance sampling technique to monitor gregarious species: A simulation exercise
de Arthur Jacquemin, David Vallecillo, Matthieu Guillemain, Pierre Defos du Rau, Jocelyn Champagnon
In Wildlife Society Bulletin, Online (November, 2022), 19
En ligne : onlinelibrary.wiley.com[...]
Wildlife count data are used to provide estimates of population abundance. To quantify changes in the size of populations, it is necessary to determine the precision of abundance estimates. Ground or aerial survey methods are often intended to be a census and thus do not provide estimates of precision. One solution is to switch approaches to a different sampling and estimation procedure, such as distance sampling. Using an example of the long-term waterfowl censuses in the Camargue, a major wintering area in southern France, we used simulation to quantify the precision and cost effectiveness of transitioning to a distance sampling approach. Based on abundance and distribution data for 14 species of waterbirds (Anatidae and coot [Fulica atra]) in the Camargue, we evaluated 5 distance sampling scenarios with parallel line transects corresponding to 5 different sampling intensities. Our results suggested that, if the objective of counts is to estimate the abundance of all waterfowl together, switching from pseudo-total to distance sampling counts would be realistic on both statistical and financial grounds. The most advantageous scenario would correspond to a sampling effort with transect lines spaced 1,000 m apart, which would allow a coefficient of variation of 0.20 for total waterfowl abundance with a 27% increase in flight costs compared to the current method. Heterogeneity in the size of detected bird groups contributed to the variability in our results, however, adjusting sampling effort from 1,750 m spaced transect to 760 m allowed reduced variation by 55%. We recommend proceeding to test flights which would allow some site-specific parameters to be refined before changing methods. However, the distance sampling method as simulated here would prove impractical to evaluate the abundance and distribution of one species alone.
de David Vallecillo, Matthieu Guillemain, Matthieu Authier, Colin Bouchard, Damien Cohez, Emmanuel Vialet, Gregoire Massez, Philippe Vandewalle, Jocelyn Champagnon
In PLOS ONE, 17(3) (March, 2022), e0265730
En ligne : journals.plos.org[...]
In the context of wildlife population declines, increasing computer power over the last 20 years allowed wildlife managers to apply advanced statistical techniques that has improved population size estimates. However, respecting the assumptions of the models that consider the probability of detection, such as N-mixture models, requires the implementation of a rigorous monitoring protocol with several replicate survey occasions and no double counting that are hardly adaptable to field conditions. When the logistical, economic and ecological constraints are too strong to meet model assumptions, it may be possible to combine data from independent surveys into the modelling framework in order to understand population dynamics more reliably. Here, we present a state-space model with an error process modelled on the log scale to evaluate wintering waterfowl numbers in the Camargue, southern France, while taking a conditional probability of detection into consideration. Conditional probability of detection corresponds to estimation of a detection probability index, which is not a true probability of detection, but rather conditional on the difference to a particular baseline. The large number of sites (wetlands within the Camargue delta) and years monitored (44) provide significant information to combine both terrestrial and aerial surveys (which constituted spatially and temporally replicated counts) to estimate a conditional probability of detection, while accounting for false-positive counting errors and changes in observers over the study period. The model estimates abundance indices of wintering Common Teal, Mallard and Common Coot, all species abundant in the area. We found that raw counts were underestimated compared to the predicted population size. The model-based data integration approach as described here seems like a promising solution that takes advantage of as much as possible of the data collected from several methods when the logistic constraints do not allow the implementation of a permanent monitoring and analysis protocol that takes into account the detectability of individuals.
de Matthieu Guillemain, David Vallecillo, Emilienne Grzegorczyk, Jean-Baptiste Mouronval, Michel Gauthier-Clerc, Alain Tamisier, Jocelyn Champagnon
In Wildlife Biology, 2021(3) (July, 2021), 8
En ligne : bioone.org[...]
The European Birds Directive (EBD) prevents hunting during spring migration, primarily to facilitate birds' use of habitats before and during the prenuptial journey. In line with the EBD requirements, the hunting season for waterfowl in southern France was shortened by two months during February–March since the mid-1950s. However, consequences of such hunting bans for late winter habitat use have not been evaluated. We investigated a 55-years dataset from a major international wintering ground to assess whether the EBD-related changes in hunting legislation have led to increased regional teal Anas crecca numbers during late winter. Teal abundance in the Camargue during late winter increased over the last decades: the ban on hunting in February was the best predictor of teal numbers during that month, leading to a sudden 50% increase in relative abundance. In March a more gradual temporal increase since the mid-1960 was instead recorded. Whether the increase in teal during late winter resulted from locally wintering birds or those from elsewhere stopping in the Camargue cannot be discerned. Nonetheless, the increase in teal numbers supports the basis for the EBD, in that a ban on hunting during late winter is associated with a greater use of habitats during this crucial part of the annual cycle, especially in February.Reliability of animal counts and implications for the interpretation of trends
de David Vallecillo, Michel Gauthier-Clerc, Matthieu Guillemain, Marion Vittecoq, Philippe Vandewalle, Benjamin Roche, Jocelyn Champagnon
In Ecology and Evolution, 11(5) (January, 2021)
En ligne : onlinelibrary.wiley.com[...]
Population time series analysis is an integral part of conservation biology in the current context of global changes. To quantify changes in population size, wildlife counts only provide estimates because of various sources of error. When unaccounted for, such errors can obscure important ecological patterns and reduce confidence in the derived trend. In the case of highly gregarious species, which are common in the animal kingdom, the estimation of group size is an important potential bias, which is characterized by high variance among observers. In this context, it is crucial to quantify the impact of observer changes, inherent to population monitoring, on i) the minimum length of population time series required to detect significant trends and ii) the accuracy (bias and precision) of the trend estimate. We acquired group size estimation error data by an experimental protocol where 24 experienced observers conducted counting simulation tests on group sizes. We used this empirical data to simulate observations over 25 years of a declining population distributed over 100 sites. Five scenarios of changes in observer identity over time and sites were tested for each of three simulated trends (true population size evolving according to deterministic models parameterized with declines of 1.1%, 3.9% or 7.4% per year that justify respectively a “declining,” “vulnerable” or “endangered” population under IUCN criteria). We found that under realistic field conditions observers detected the accurate value of the population trend in only 1.3% of the cases. Our results also show that trend estimates are similar if many observers are spatially distributed among the different sites, or if one single observer counts all sites. However, successive changes in observer identity over time lead to a clear decrease in the ability to reliably estimate a given population trend, and an increase in the number of years of monitoring required to adequately detect the trend. Minimizing temporal changes of observers improve the quality of count data and help taking appropriate management decisions and setting conservation priorities. The same occurs when increasing the number of observers spread over 100 sites. If the population surveyed is composed of few sites, then it is preferable to perform the survey by one observer. In this context, it is important to reconsider how we use estimated population trend values and potentially to scale our decisions according to the direction and duration of estimated trends, instead of setting too precise threshold values before action.
de David Vallecillo
Montpellier : Université de Montpellier, 2021, 263
De nombreux programmes de suivis utilisent des données de comptage pour quantifier et prévoir les tendances temporelles et spatiales d’évolution des estimations d’abondance. L’objectif principal est d’identifier les espèces nécessitant le plus d'attention en matière de conservation et de gestion. Les méthodes de comptage sont rarement en mesure de fournir des tailles de population absolues, poussant à recourir à l’échantillonnage de la population concernée. Par définition, les données collectées dans tout protocole d’échantillonnage présentent des biais, il est donc important d’évaluer l’influence des biais de comptage sur la compréhension de la dynamique spatio-temporelle de la faune sauvage. À travers cette thèse, nous avons étudié l’influence des biais de comptage (erreur d’estimation des groupes et détection imparfaite des individus) sur les estimations d’abondance d’espèces grégaires et pris en compte ces biais pour modéliser les évolutions de répartition spatiale au cours du temps. Pour cela, nous avons utilisé une série de données exceptionnelle, de par sa couverture spatiale et temporelle, de comptages d’oiseaux d’eau en Camargue, au sud de la France. Cette thèse s’articule autour de 2 sections. La première section visait à mieux comprendre le processus d’observation qui génère les données de comptage. Cette recherche méthodologique a porté sur l'amélioration de la collecte des données afin de réduire les biais et/ou d'accroître la précision des estimations d’abondance, et sur le développement de méthodes statistiques capables de prendre en compte les biais ou l'incertitude des données collectées. Le premier article de cette section a montré à quel point il est important de considérer et minimiser les changements d’observateurs dans le temps lorsque l’on souhaite évaluer les tendances d’espèces grégaires, compte tenu de l'erreur d'estimation de la taille des groupes. Dans le deuxième article, nous avons développé un modèle combinant des données de comptage de sources différentes (aérienne et terrestre) afin de prendre en compte la détection imparfaite des individus tout en considérant les surestimations (double comptage, erreur d’identification) qui peuvent survenir durant les comptages. Le troisième article a révélé que la mise en place d’une méthode d’échantillonnage par distance de détection est réaliste d’un point de vue à la fois statistique et économique pour des espèces grégaires caractérisées par une forte hétérogénéité spatiale dans la distribution des groupes. Cependant, la capacité de cette méthode à estimer précisément l’abondance par espèce reste à démontrer. Sur la base de cette première section, la seconde section de cette thèse visait à mieux comprendre les mécanismes écologiques d'évolution temporels et spatiaux de l’abondance de la Sarcelle d’hiver (Anas crecca) dans le delta de Camargue. Le quatrième article applique les modèles développés ci-avant pour montrer que des changements rapides (d’une saison d’hivernage à une autre) dans la gestion hydraulique d’une unité fonctionnelle (remise diurne et zones de gagnages nocturnes à proximité) influencent directement les variations annuelles des effectifs de Sarcelles d’hiver sur la remise. Le cinquième article a montré que l'arrêt de plus en plus précoce de la chasse au cours des 50 dernières années a conduit à une plus grande utilisation de la région par la Sarcelle en début de printemps. Les résultats obtenus en termes de compréhension des méthodes de comptage, de l’écologie des anatidés et de réflexion sur l’évolution des pratiques de gestion des zones humides pourront être mobilisés à l’échelle nationale et internationale pour mieux gérer les espèces grégaires, leurs habitats et la biodiversité associée.
de David Vallecillo, Pierre Defos du Rau, Anthony Olivier, Jocelyn Champagnon, Matthieu Guillemain, Nicolas Croce, Gregoire Massez, Jérémiah Petit, Nicolas Beck, Jean-Yves Mondain-Monval
In Faune sauvage, 323 (Avril-Juin, 2019), 33-39
En Camargue, plusieurs groupes de chasseurs ont expérimenté des changements dans leurs modalités de gestion des habitats et des prélèvements, dans l'objectif de pratiquer une activité cynégétique à la fois plus durable et plus favorable à la biodiversité. Quelques exemples de ces différentes pratiques mises en oeuvre sur cinq territoires sont présentés dans cet article.
