Résumé
Climate seasonality is a predominant constraint on the lifecycles of
species in alpine and polar biomes. Assessing the response of these
species to climate change thus requires taking into account seasonal
constraints on populations. However interactions between seasonality,
weather fluctuations, and population parameters remain poorly explored as
they require long-term studies with high sampling frequency. This study
investigated the influence of environmental covariates on the demography
of a corvid species, the alpine chough Pyrrhocorax graculus, in the highly
seasonal environment of the Mont Blanc region. In two steps, we estimated:
1) the seasonal survival of categories of individuals based on their age,
sex, etc., 2) the effect of environmental covariates on seasonal survival.
We hypothesized that the cold season – and more specifically, the end of
the cold season (spring) – would be a critical period for individuals, and
we expected that weather and individual covariates would influence
survival variation during critical periods. We found that while spring was
a critical season for adult female survival, it was not for males. This is
likely because females are dominated by males at feeding sites during
snowy seasons (winter and spring), and additionally must invest energy in
egg production. When conditions were not favourable, which seemed to
happen when the cold season was warmer than usual, females probably
reached their physiological limits. Surprisingly, adult survival was
higher at the beginning of the cold season than in summer, which may
result from adaptation to harsh weather in alpine and polar vertebrates.
This hypothesis could be confirmed by testing it with larger sets of
populations. This first seasonal analysis of individual survival over the
full life cycle in a sedentary alpine bird shows that including
seasonality in demographic investigations is crucial to better understand
the potential impacts of climate change on cold ecosystems.