Estimating Population Growth and Recruitment Rates Across the Range of American Common Eiders

Abstract

Sound management of bird populations rests upon an adequate understanding of their population dynamics. Our study evaluated recruitment and population growth rates of 14 American common eider (Somateria mollissima dresseri) colonies from Labrador, Nova Scotia, Quebec, Canada, and Maine, USA, during various periods between 1970 and 2019. We used Pradel mark‐recapture models to estimate colony‐specific growth rates and the relative contributions of survival and recruitment on growth. We also validated this approach using annual nest counts (~8,000 pairs) conducted between 2003 and 2019 during down harvest operations in 3 colonies located in the Saint Lawrence estuary in Quebec. There was generally a good agreement between estimates derived using the 2 approaches. We considered that capture‐recapture data were suitable to estimate population trends of common eiders in other colonies, especially for colonies where accurate nest monitoring is impaired by dense vegetation. The breeding abundance declined at major colonies in Maine and Nova Scotia and increased or was stable in Quebec and Labrador. Female survival contributed the most to population growth, but variation in recruitment among colonies was more important than variation in survival to explain population growth. Management measures should thus strive to maximize local recruitment in colonies with declining populations. The assumption that apparent survival probabilities were homogeneous throughout an individual capture history was violated at several colonies in Quebec and Labrador. Using recaptures and band recoveries, we showed that the lower apparent survival for newly marked individuals compared to females that had been recaptured at least once was caused by a difference in site fidelity rather than true survival. But <1% of recaptured females dispersed to another colony for breeding, indicating that the lower site fidelity could be related to heterogeneity in capture probability among individuals. © 2021 The Wildlife Society.

Extension of Pradel capture–recapture survival‐recruitment model accounting for transients

“…Yet, the presence of transient individuals is very common in many taxa (Oro & Doak, 2020), and the bias they produce in demographic rates may be substantial (Orgeret et al., 2014). The well‐known and widely used original Pradel (1996) temporal symmetry model for CMR data to estimate survival, recruitment and population growth was designed for resident individuals only, but some studies have used it on data with transient individuals, while being aware of the risk of bias in survival and recruitment estimates (Giroux et al., 2021; Rodrigues et al., 2021; Tenan et al., 2014). Another study reported poor model fit (Sasso et al., 2006).…”

“…For the Pradel model, though, a solution accounting for transients was not available, and this has often been mentioned as a limitation of the Pradel model (Ahrestani et al., 2017; Saracco & Rubenstein, 2020). Many studies using the Pradel model have found the presence of transience, but have not been able to address it properly (Giroux et al., 2021; Rodrigues et al., 2021; Tenan et al., 2014). Using the original Pradel model on data with transients leads to a strong bias in the estimates of survival, seniority (and thus also recruitment) and capture probability (Orgeret et al., 2014), which can lead to poor model fit (Sasso et al., 2006).…”

Learnings from collaborative monitoring of remote wildlife populations: factors affecting changes in number and distribution of nesting Hudson Bay eiders ducks in the Belcher Islands

“…It is unlikely that subsistence hunting by the residents of Sanikiluaq has prevented an increase in population size. In long-lived birds, such as common eiders, adult survival is the parameter contributing the most to population growth (Giroux et al, 2021;Wilson et al, 2012).…”

“…Factors affecting the reproduction success and overall recruitment of Hudson Bay eiders could have had an impact on population growth and recovery. The adult survival rates of the common eider population are usually high (between 0.8 and 0.95) and relatively stable through time (Giroux et al, 2021;Hario et al, 2009;Wilson et al, 2007;Wood et al, 2021). For eiders, while the adult survival rates contribute the most to population growth (Giroux et al, 2021;Wilson et al, 2012), studies have shown that the recruitment rate is a stronger determinant of the variability in population growth rate (Giroux et al 2021;Hario et Rintala, 2006).…”

“…The adult survival rates of the common eider population are usually high (between 0.8 and 0.95) and relatively stable through time (Giroux et al, 2021;Hario et al, 2009;Wilson et al, 2007;Wood et al, 2021). For eiders, while the adult survival rates contribute the most to population growth (Giroux et al, 2021;Wilson et al, 2012), studies have shown that the recruitment rate is a stronger determinant of the variability in population growth rate (Giroux et al 2021;Hario et Rintala, 2006). Some studies also showed that female survival is not the main factor driving population increase (Coulson, 1984) or decrease (Hario et al, 2009).…”