Biology subjects

Pradel, R.

Publications and source records attributed to Pradel, R..

6 recordsLinked to original sources

bioRxiv2026

Harvest probabilities of European ducks: the very first estimation based on reward rings

Ringing-recoveries are an overarching element of population dynamic studies that allow estimating mortality causes and hence improve wildlife management. However, possible drawbacks of recovered rings reside in the fact that reporting probability is rarely known, but consistently lower than 100%. Thus, estimating harvest probabilities (mortality probability due to harvesting) of exploited species without knowledge of ring reporting probability by people exploiting these animals is not straightforward. We here provide the first ever reward-ring study carried out to evaluate European reporting probabilities, hence European harvest probabilities, in three species of ducks (Mallard Anas platyrhynchos, Eurasian Teal A. crecca and Common Pochard Aythya ferina). The 70 Euros reward on some rings was considered to yield a total return of the rings, allowing by comparison to evaluate the reporting probability of standard rings. After the initial year of ringing, annual reporting probability was very similar among the three species, at 0.63-0.66, suggesting two-thirds of the found rings are sent back to the ringing centre. This allowed computation of the annual harvest probability, which was up to 0.27 during the first months after ringing in fall but decreased to 0.04-0.10 during later years. Compared to North American results, the present estimates suggest birds are submitted to a heavy hunting mortality during the first months after ringing, but this pressure declines in later years, likely owing to counter selection of vulnerable/exposed individuals and/or learning by the birds.

ecology↗

bioRxiv2024

Estimating population size with repeated observations of non-invasive sampling in presence of misidentification

Although non-invasive sampling is increasingly used in capture-recapture (CR) monitoring, it carries a risk of misidentification that, if ignored, causes an overestimation of population size. Models that deal with misidentification have been proposed. However, these models assume that only one sample can be collected per individual at one occasion. This is not true for several monitoring programs based on DNA, for example for those that extract the DNA from faecal samples. The models do not take repeated observations into account, leading to biased estimates. In this paper, we develop an approach that extends the latent multinomial model (LMM) of Link et al., 2010 using a Poisson distribution to model the number of samplings of the same individual on a given occasion. We then conduct simulations to test how our new model performs. As an illustration, we applied the new Poisson model to a collection of Eurasian otter faeces (Lampa et al., 2015). Our model yields unbiased estimates of population size when the expected number of samples per individual ({lambda}) is sufficiently high: simulations with{lambda} [≥] 0.36 and five capture occasions or with{lambda} [≥] 0.23 and seven or more occasions. In contrast, when{lambda} = 0.11 (corresponding to about 42%, 53% and 62% of the individuals being detected with respectively 5, 7 and 9 occasions), the population size is consistently underestimated. Applying the model to the otter dataset confirms the presence of misidentifications, consistent with the authors expectations. Our findings indicate that repeated observations can be modelled without bias. The application on otters shows that our model is necessary to accurately estimate population size in presence of misidentification and repeated observations.

ecology↗

bioRxiv2020

When to depart from a stopover site? Time-since-arrival matters more than weather conditions

On the journey to wintering sites, migratory birds usually alternate between flights and stopovers where they rest and refuel. Migration strategies are assumed to differ according to season: a time-minimization pre-breeding migration strategy towards breeding locations, and an energy-minimization post-breeding migration strategy to wintering ones. The duration of flights and stopovers determines the energy requirements and the total duration of the journey. Since migrating birds actually spend most of the time at stopovers, selection to minimize the amount of energy or time spent on migration is very likely to operate on the effectiveness of stopover rest and refueling. Here we address the relative contribution of factors to departure decisions from stopover sites during the post-breeding migration in a long-distance migratory songbird. When capture probability is low it is impossible to assess the variation in body condition over the entire duration of the stopover. To get around this, we use Time Since Arrival (TSA) as a proxy for the changes in the state of individuals during the stopover. We propose that TSA is an integrative proxy for resting, feeding and fattening efficiency. We develop a capture-recapture model to address the relationship between departure probability, estimated TSA, and weather conditions. Using a 20-year dataset from sedge warblers, we show that TSA has a larger effect on departure probability than weather conditions. Low humidity and an increase in atmospheric pressure in the days preceding departure are associated with higher departure probability, but these effects are smaller than that of TSA.

ecology↗

bioRxiv2019

Changes in social cohesion in a long-lived species under a perturbation regime

O_LIUnderstanding the behaviour of a population under perturbations is crucial and can help to mitigate the effects of global change. Sociality can influence the dynamics of behavioural processes and plays an important role on populations resilience. However little is known about the effects of perturbations on the social cohesion of group-living animals.\nC_LIO_LITo explore the strength of social cohesion and its dynamics under perturbations, we studied an ecological system involving a colonial, long-lived species living in a site experiencing a shift to a perturbed regime. This regime, caused by the invasion of predators, led this colony to hold from 70% to only 3% of the total world population in only one decade. Because birds breed aggregated in discrete and annually changing patches within large colonies, we could disentangle whether annual aggregation was random or resulted from social bonding among individuals. Our goals were 1) to uncover if there was any long-term social bonding between individuals and 2) to examine whether the perturbation regime affected social cohesion.\nC_LIO_LIWe explored social cohesion by means of contingency tables and, within the Social Network Analysis framework, by modeling interdependencies among observations using additive and multiplicative effects (AME) and accounted for missing data. We analysed 25 years of monitoring with an individual capture-recapture database of more than 3,500 individuals.\nC_LIO_LIWe showed that social bonding occurs over years in this species. We additionally show that social bonding strongly decreased after the perturbation regime. We propose that sociality and individual behavioural heterogeneity have been playing a major role driving dispersal and thus population dynamics over the study period.\nC_LIO_LIPerturbations may lead not only to changes in individuals behaviours and fitness but also to a change in populations social cohesion. The demographic consequences of the breaking down of social bonds are still not well understood, but they can be critical for population dynamics of social species. Further studies considering individual heterogeneity, sociality and different types of perturbations should be carried out to improve our understanding on the resilience of social species.\nC_LI

ecology↗

bioRxiv2019

Modeling the demography of species providing extended parental care: A capture-recapture approach with a case study on Polar Bears (Ursus maritimus)

O_LIIn species providing extended parental care, one or both parents care for altricial young over a period including more than one breeding season. We expect large parental investment and long-term dependency within family units to cause high variability in life trajectories among individuals with complex consequences at the population level. So far, models for estimating demographic parameters in free-ranging animal populations mostly ignore extended parental care, thereby limiting our understanding of its consequences on parents and offspring life histories. C_LIO_LIWe designed a capture-recapture multi-event model for studying the demography of species providing extended parental care. It handles statistical multiple-year dependency among individual demographic parameters grouped within family units, variable litter size, and uncertainty on the timing at offspring independence. It allows to evaluate trade-offs among demographic parameters, the influence of past reproductive history on the caring parent survival status, breeding probability and litter size probability, while accounting for imperfect detection of family units. We assess the model performances using simulated data, and illustrate its use with a long-term dataset collected on the Svalbard polar bears (Ursus maritimus). C_LIO_LIOur model performed well in terms of bias and mean square error and in estimating demographic parameters in all simulated scenarios, both when offspring departure probability from the family unit occurred at a constant rate or varied during the field season depending on the date of capture. For the polar bear case study, we provide estimates of adult and dependent offspring survival rates, breeding probability and litter size probability. Results showed that the outcome of the previous reproduction influenced breeding probability. C_LIO_LIOverall, our results show the importance of accounting for i) the multiple-year statistical dependency within family units, ii) uncertainty on the timing at offspring independence, and iii) past reproductive history of the caring parent. If ignored, estimates obtained for breeding probability, litter size, and survival can be biased. This is of interest in terms of conservation because species providing extended parental care are often long-living mammals vulnerable or threatened with extinction. C_LI

ecology↗

bioRxiv2017

R2ucare: An R package to perform goodness-of-fit tests for capture-recapture models

O_LIAssessing the quality of fit of a statistical model to data is a necessary step for conducting safe inference.\nC_LIO_LIWe introduce R2ucare, an R package to perform goodness-of-fit tests for open single-and multi-state capture-recapture models. R2ucare also has various functions to manipulate capture-recapture data.\nC_LIO_LIWe remind the basics and provide guidelines to navigate towards testing the fit of capture-recapture models. We demonstrate the functionality of R2ucare through its application to real data.\nC_LI

ecology↗