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Oiseaux chanteurs des milieux ouverts de montagne et changements globaux

Abstract : Growth of human populations and economy causes human societies to be more and more dependent on ecosystem services. Understand the mechanisms underlying the response of biological systems to global changes is thus a scientific and social issue. This research was thank and realized when developing a long term monitoring scheme for mountain birds with different research teams and conservation stakeholders. In this long term monitoring, birds are used as indicators of the effects of global changes on biodiversity. Mountain massifs of France are exposed to climate change, and land use evolution, as livestock grazing is dependent on raw material prices and public support. Mountains are interesting, but contingent, ecological contexts to study the effects of global changes on biodiversity, due to the sharp bioclimatic gradients and facet landscapes. My main objective was to characterize and quantify the respective effects of temperature, vegetation structure, and livestock grazing activities on this bird community, to better predict the consequences of major climate and land use changes. Elevation gradient have been mostly studied in isolated sites and large elevation gradients. Following our main objective, in the first chapter, we chose the opposite approach, by multiplying study sites in a standardized habitat (open grasslands, 1100 point counts in Alps and Pyrenees). Our results show that primary productivity, temperature and habitat structure all influence the bird community. Also 5 out of the 8 most common species seemed to be favorited by livestock grazing activities. In the second chapter, I tested the effect of the strong seasonality typical from temperate mountains’ climate, by testing it’s effect on the survival of individuals in a population of alpine Choughs Pyrrhocorax graculus. I relied on the CMR survey of more than 1000 individuals carried out by Anne Delestrade during 30 years. Choughs show the highest survival known in corvids, with a seasonal pattern, in interaction with individuals’ states like sex group. Adult females also showed lower spring survival after warm winters. In third chapter I speculated on the ability of insectivorous passerines to get benefit from the presence of large domestic herbivorous mammals, by eating coprophagous insects. I measured the stable nitrogen isotopic ratios in the feces of most common birds to provide an estimation of the trophic level of birds’ preys, and thus test my hypothesis and eventually quantify the mechanism. We observed, in both mountain massif, a shift from herbivorous from higher trophic level insects catched by birds, from locations with low grazing intensity to those with high grazing intensity. The last chapter present an evaluation of the potential of adaptive niche based sampling to increase the ability to find rare species in new localities. This study includes simulations and field test in the Pyrenees mountains on two alpine bird species, Snowfinch Montifringilla nivalis and rock Thrush Monticolla saxatilis. Results show the strong potential of the method in the field, and its limit, with an increase in specificity at the cost of omissions that also increase. As a general discussion, I develop research perspective to generalize the strong link found between birds’ diet and large mammalian herbivores, and to better understand the phenology of populations facing unpredictable snow cover during breeding period.
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  • HAL Id : tel-02860834, version 1

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Jules Chiffard. Oiseaux chanteurs des milieux ouverts de montagne et changements globaux. Milieux et Changements globaux. Université Paris sciences et lettres, 2019. Français. ⟨NNT : 2019PSLEP038⟩. ⟨tel-02860834⟩

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