When survival matters: is decreasing survival underlying the decline of common pochard in western Europe?

Abstract

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Long‐term increase in female body condition and its effect on reproduction in two European red‐listed species, Common Pochard (Aythya ferina) and Tufted Duck (Aythya fuligula)

“…Folliot et al . (2020) failed to confirm changes in adult survival as the main explanatory variable of a decline in Common Pochard populations. A lower proportion of breeding females within populations – resulting in higher male bias in the adult sex ratio (Brides et al .…”

“…The long-term changes in BCI of females in the late stage of incubation and the consequent effect on breeding success are crucial for an assessment of population dynamics (Johnson et al 1992, Newton 2013, especially for globally declining species such as Common Pochard and Tufted Duck (Musil & Fuchs 1994, Musil & Neužilová 2009, Fox et al 2016, Elmberg et al 2020, Folliot et al 2020, Keller et al 2020, IUCN 2022). Based on the analysis of body condition in late-incubating females, our study shows evidence of improvement in the body condition both in Common Pochard and in Tufted Duck over 17 years.…”

“…Contrary to previous studies showing a clear association between female body condition and widespread declines in a North American Aythya species (Lesser Scaup Aythya affinis; Anteau & Afton 2004), our results show that population declines cannot be directly linked to changes in body condition, as we found an increasing trend in BCI. Folliot et al (2020) failed to confirm changes in adult survival as the main explanatory variable of a decline in Common Pochard populations. A lower proportion of breeding females within populationsresulting in higher male bias in the adult sex ratio (Brides et al 2017, Frew et al 2018, Pöysä et al 2019)has been observed in many duck species.…”

Assessing spatiotemporal variation in abundance: A flexible framework accounting for sampling bias with an application to common pochard (Aythya ferina)

“…Our analyses do not support this view for pochards in the northwestern flyway where the decline in wintering individuals was in fact significantly stronger at northern than southern latitudes (−12% per year at 60° of latitude against stability at 46°). According to ringing recoveries, large proportions of pochards wintering in Northwestern Europe originate from beyond or up to the Ural Mountains (Folliot et al, 2020 ), casting serious doubt about the pertinence of the three putative flyways as delineated by Scott and Rose ( 1996 ). Thus, we cannot totally rule out that the decline in pochard in Northwestern Europe is due to individuals staying closer to their breeding grounds thereby evading the survey by remaining outside the putative flyway where most IWC counts are carried out.…”

“…This diving duck is considered to have experienced a sharp decline over most of its range including the focal flyway (mean annual declines of −5.97% and −2.16% in the Northwestern and Central European Flyways, respectively, as estimated with TRIM, 2003–2012, Nagy et al, 2014 ). Such unfavorable status has caused the species to be upgraded from Least Concern (LC) to Vulnerable (VU) on the European and global IUCN Red Lists in 2015 (BirdLife International, 2015 ), and demographic studies to be initiated (Caizergues et al, 2016 ; Folliot et al, 2017 , 2018 , 2020 ; Gourlay‐Larour et al, 2012 , 2013 , 2014 ; Keller, 2009 ).…”