DOI: 10.5061/dryad.0vt4b8gz5
title: Red-billed chough (Pyrrhocorax pyrrhocorax) models

description: The absence of a species in apparently suitable regions is often
 attributed to habitat deterioration, which, according to the
 IUCN-guidelines, would preclude reintroduction unless the habitat is
 sufficiently restored. The crux is therefore to determine species’ key
 habitat requisites and to localize potentially restorable sites based on
 the habitat selection of thriving populations in similar environments. The
 distribution of the Red-billed chough (Pyrrhocorax pyrrhocorax) in the
 Alpine arch is currently restricted to its western side. The eastern Alps
 have only been occupied sporadically during past centuries, which
 triggered a discussion around reintroduction. The fact that the last
 confirmed pairs bred at middle elevation, in derelict buildings instead of
 alpine cliffs, suggested a lack of habitat suitability in the uplands. To
 test this hypothesis, we modelled seasonal foraging habitat (during
 winter, breeding and dispersal) and nest site-selection in the western
 Swiss Alps using long-term observation data together with a wide palette
 of environmental predictors. The models were extrapolated to eastern
 Switzerland to estimate the quality and extent of the available habitat.
 Both foraging and nesting habitats were predicted with a high level of
 accuracy (AUC &gt; 0.8). Despite variation between seasons,
 south-exposed dry meadows and extensively-grazed pastures were always
 preferred as foraging habitat, while forested and snow-covered areas were
 avoided. Availability of, and distance to suitable foraging habitats were
 the main determinants of nest-site selection, probably reflecting strong
 energetic constraints during reproduction. However, the extrapolation to
 eastern Switzerland revealed an even higher overall amount and relative
 percentage of all habitat types. One explanation could be that our
 predictors were too coarse to encapsulate qualitative, structural or
 compositional differences of the grasslands. However, the results could
 also point to an alternative hypothesis, namely that post-glacial
 recolonization patterns, in particular the absence of nearby source
 populations, precluded the occupation of the eastern Alps.
description: Species data: Red-billed chough foraging
 locations for the years 2000 to 2014 were extracted from the database of
 the Swiss Ornithological Institute (www.ornitho.ch), which contains
 opportunistically collected observations from amateur bird watchers and
 professional ornithologists. Only locations with a minimum accuracy of
 100m and ascertained foraging activity were retained (Fig. 1). The dataset
 was subdivided into three seasons: winter (November-April, N = 140),
 breeding (May-July, N = 193) and post-breeding dispersal (August-October,
 N = 78). Nest site locations (N = 76) were based on long-term, annual
 field surveys conducted from 1974 to 2016, mostly by one of the co-authors
 (P.-A.O.). Due to conservation reasons these sensitive data are only
 available upon request. Environmental
 variables: The environmental variables included in at
 least one of the models encompassed inormation on topography, climate,
 snow condition and land cover, including human infrastructure. Topography
 was described by slope and exposition (i.e. northness and eastness,
 defined as cosine and sine of aspect) as derived from the digital
 elevation model of Switzerland. Climate information included the
 precipitation in summer and winter, as obtained from the worldclim-dataset
 (www.worldclim.org), downscaled to a 100m resolution based on the SRTM-V4
 digital elevation model (DEM) and the method described in Zimmermann
 & Roberts (2001). Snow cover data for the years 2006-2011 were
 generated by the WSL Institute for Snow and Avalanche Research SLF
 according to (Bavay et al. 2013). This model, based on the underlying
 alpine surface process model Alpine3D (Lehning et al. 2006) and the
 SNOWPACK model (Fierz and Lehning 2001) provided daily snow cover data at
 a spatial resolution of 200x200m. Monthly values of snow cover were
 calculated by averaging the values of four days randomly selected from
 each of the four weeks per study month, to account for within-month snow
 cover heterogeneity. We then calculated the average percentage of area
 covered by snow within 1 km2 (radius = 564m) for each of the study months
 separately. Information on land cover, i.e. the
 percentage of forest, grassland, waterbodies, glaciers, scree and rock was
 obtained from the Vector 25 map (SWISSTOPO 2009). In addition, we
 calculated the distance to steep rock (&gt;45°). Dry meadows and
 pastures were adopted from the mapping of the Swiss Federal Administration
 of the Environment (https://www.bafu.admin.ch). In addition, we calculated
 the mean number of sheep and goat per community in the years 2004-2014, as
 obtained from the Swiss Federal Administration for Statistic Switzerland
 (BfS) (https://www.bfs.admin.ch) and related them to the amount of
 pastureland per community in order to obtain a rough estimate of the
 density of livestock per hectare of pastureland. Human infrastructure was
 included as the distance to transportation infrastructure (roads and
 railways), ski-lifts and cableways as obtained from the Vector 25
 map. All predictor variables were prepared as raster
 maps (cell size: 25x25m). In order to capture the environmental conditions
 prevailing around the foraging locations, but at the same time to both
 account for sampling accuracy and avoid pseudo-accuracy given the original
 resolution of some of the predictor variables (see Read_Me.docx), we
 calculated means (continuous variables), percentages (boolean and
 categorical variables) or densities (for point and linear features) within
 a circular moving window with a radius 100m. Snow cover heterogeneity was
 considered within a 1km2 area (radius = 564m). For the nest site model,
 for which we had accurate nest locations, we used the data of rocks and
 slope at the original 25m resolution. In addition, to
 test whether the amount of, and distance to suitable foraging habitat
 affected nest site selection, we generated additional variables, directly
 drawn from the breeding-foraging habitat model. First, we calculated the
 average suitability of foraging habitat (i.e. Maxent logistic output)
 within a 3-km radius around the nest site, which roughly corresponds to
 the distance birds use for foraging. Second, we converted this continuous
 variable into a binary map of nest site presence and absence (as specified
 below) and calculated the distance of the nest to the next foraging
 patch. References:
 BAVAY, M., GRUENEWALD, T. and LEHNING, M. 2013. Response of snow
 cover and runoff to climate change in high Alpine catchments of Eastern
 Switzerland. -Advances in Water Resources, 55: 4-16.
 FIERZ, C. and LEHNING, M. 2001. Assessment of the micro
 structure-based snow-cover model SNOWPACK: thermal and mechanical
 properties. -Cold Regions Science and Technology, 33: 123-131.
 LEHNING, M., VOLKSCH, I., GUSTAFSSON, D., NGUYEN, T. A., STAHLI,
 M. and ZAPPA, M. 2006. ALPINE3D: a detailed model of mountain surface
 processes and its application to snow hydrology. -Hydrological Processes,
 20: 2111-2128. ZIMMERMANN, N. E. and ROBERTS, D.
 W. 2001. Final Report of the MLP climate and biophysical mapping project.
 Birmensdorf, pp. 18.