Biology subjects

Guillemain, M.

Publications and source records attributed to Guillemain, M..

3 recordsLinked to original sources

bioRxiv2026

Is hidden demographic heterogeneity pervasive? Harvested birds as an example

Individual demographic heterogeneity refers to the fact that individuals from a given population exposed to similar environmental conditions express different demographic traits or tactics. This heterogeneity can either be linked to factors/states such as age, sex or body condition, or be due to hidden factors/states not immediately apparent or easily characterized (hereinafter referred to as 'hidden heterogeneity'). Yet accounting for demographic heterogeneity, and more particularly heterogeneity in survival is crucial because it is an important mechanism underlying compensation processes between natural and harvest mortality. In this study, we used capture-mark-recapture-recovery data of 6 hunted species covering a large range of the demographic slow-fast continuum (61,432 individuals ringed from 1953 to 2020 among Common Teal Anas crecca, Mallard A. platyrhynchos, Common Pochard Aythya ferina, Common Snipe Gallinago gallinago, Common quail Coturnix coturnix, and Blackbird Turdus merula), to assess the presence of unexplained heterogeneity in survival with multievent models. We detected hidden survival heterogeneity in most species, even though the differences between the high and low categories of survival were often small. The probability for an individual to display a low vs high survival rate was not related to potentially important individual factors/states such as migration phenology or to morphology. The presence of hidden heterogeneity was pervasive, affecting species distributed along a relatively large spectrum of demographic strategies. This, in our opinion, supports that part of this heterogeneity in survival evidenced in our study is indeed hidden, resulting either from hidden intrinsic (inherent) individual differences of survival among individuals, or hidden extrinsic factors e.g., linked to spatial variations in hunting pressure. Our findings suggest that hidden heterogeneity needs to be explored more thoroughly in huntable species and accounted for in management policies.

ecology↗

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

Delayed dichromatism as a convenient tool to disentangle the effects of survival and productivity on the population dynamics in waterfowl

Monitoring the number of individuals is by far the most popular strategy for studying the environmental factors that determine population dynamics and for measuring the effectiveness of management actions aimed at population recovery, control or eradication. Unfortunately, population size monitoring is inefficient in identifying the mechanisms underlying demographic processes and, in particular, in assessing the extent to which population growth rate is influenced by changes in adult survival rather than variations in reproductive parameters. In many waterfowl species, sexual dichromatism is observed in adults, while immatures of both sexes display a plumage pattern similar to that of adult females. In these species, the apparent proportion of males increases as the female-like immature males gradually take on the plumage of adult males. The difference between the apparent sex ratio before and after the young reach sexual maturity then provides information about the age ratio of a population. Using winter counts that distinguished between female-like and male-like individuals of two non-native populations of Ruddy duck Oxyura jamaicensis, a species that exhibits such a plumage pattern, we present a non- invasive method based on the apparent sex ratio to split population growth rate into adult survival and recruitment rates (the latter also referred to as productivity). This method can correctly detect annual changes in vital rates, supporting the assumption that counts conducted in an appropriate time window reflect the age structure of a population. We exemplify how the respective contributions of survival and productivity to the population growth rate are essential for understanding the processes behind demo- graphic dynamics. Finally, we point out some best practices to correctly apply the "apparent sex ratio" method described here.

ecology↗