Negative effects of snow cover on foraging habitat selection and breeding success in the Red-billed Chough Pyrrhocorax pyrrhocorax
Published: Volume 69.1, January 2022. Pages 59-74.
The Red-billed Chough, a species of conservation priority in Europe, is threatened by habitat encroachment, decline of pastoralism, heavy use of pesticides and disturbance by recreational activities. Its future greatly depends on the quality of its remaining habitat, particularly in mountains where no previous study has explored the effects of climate and snow condition on its populations. In the Gavarnie Special Protection Area (9,300ha, Pyrenees National Park), a highly mountainous open landscape mainly covered by grassland, alpine moorland, screes and rocks, we compared the reproductive success of Red-billed Choughs during two very contrasted years, 2013 and 2014, in terms of snow phenology in spring. We also evaluated foraging habitat selection during the young rearing period. Habitat selection was estimated by modelling the probability, for 50 Å~ 50m2 spatial units sampled in the study area, of being observed to be used by choughs for foraging. Breeding success was much lower during the year with prolonged spring snow cover, especially at higher elevation: 11 breeding pairs were present, compared to 22 pairs during the following year when snow cover phenology was more typical. Nesting phenology was delayed by ten days in the year with prolonged snow cover. Variables that positively influenced the probability for choughs to use spatial units as feeding areas were mostly linked with the presence of low vegetation (herbaceous or mixed scrub and grassland areas, grazed areas), and the absence of snow (time of snow cover during study period, exposure to solar radiation, presence of wetlands). we suggest that snow cover at the end of the cold season can create a spatial mismatch between customary chough nest locations at high elevations and areas suitable for foraging. The consequence is a scarcity of nesting attempts and low breeding success in the mountainous areas during years with prolonged and high altitude snow cover in spring. we also use these results to suggest the potential for this species to be used as an indicator for the effects of changes in climate and pasture grazing practices.