The importance of seasonal environmental factors in the foraging habitat selection of Alpine Ring Ouzels Turdus torquatus alpestris

Abstract

Species inhabiting mountain ecosystems are expected to be particularly vulnerable to environmental change, yet information on their basic ecology is often lacking. Knowledge from field‐based empirical studies remains essential to refine our understanding of the impact of current habitat alterations and for the consequential development of meaningful conservation management strategies. This study focuses on a poorly investigated and vulnerable mountain bird species in Europe, the Ring Ouzel Turdus torquatus. Our aim was to identify the species’ key ecological requirements during the crucial period of nestling provisioning in the context of environmental change. We radiotracked and observed Alpine Ring Ouzels in a high‐density population, investigating their pattern of foraging habitat selection in 2015 and 2017, and evaluated the transferability of these results over a wider geographical range across the SW Swiss Alps. Foraging birds selected, consistently in space and time, short grass swards (< 10 cm) with interspersed patches of accessible and penetrable soils, at intermediate moisture levels (around 40–65% volumetric water content). In Alpine ecosystems, this microhabitat configuration is typically widespread during the spring snowmelt, but extremely seasonal, with a rapid decrease in its availability over the course of the breeding season. This underlines the high vulnerability of the Ring Ouzel to environmental change: an earlier snowmelt could generate a temporal mismatch between the peak of the breeding effort and optimal foraging conditions; however, abandoning grazing activities on semi‐wooded Alpine pastures may further decrease foraging habitat suitability through taller and denser grass swards, and subsequent woody vegetation encroachment. This study provides a mechanistic appraisal of the challenges Ring Ouzels will face in the future, as well as initial guidelines for targeted habitat management within timberline ecotones.

Clinging on to alpine life: Investigating factors driving the uphill range contraction and population decline of a mountain breeding bird

“…In contrast, at higher elevations, dotterel frequently occupy J. trifidus heaths, which may be less affected by nitrogen deposition (Fremstad, Paal, & Möls, 2005), while wind ablation and limited availability of other minerals also have the potential to buffer against vegetation change and maintain low vegetation swards at high elevations (Britton, Beale, Towers, & Hewison, 2009; Ross, Woodin, Hester, Thompson, & Birks, 2012). We tentatively suggest, therefore, as a prompt for future research, that nitrogen deposition‐driven changes in both vegetation composition and sward height may render low‐elevation areas in particular less suitable not just for dotterel but the wider suite of alpine birds that demonstrate strong habitat preferences for low‐growing alpine vegetation types (Barras et al, 2019; Brambilla et al, 2017; Resano‐Mayor et al, 2019; Revermann, Schmid, Zbinden, Spaar, & Schröder, 2012).…”

Nestling diet and parental food provisioning in a declining mountain passerine reveal high sensitivity to climate change

“…In the UK, one of the underlying mechanisms is believed to be warmer summers that reduce prey availability after the breeding season (Beale et al 2006). In effect, ring ouzels rely on specific habitat characteristics for efficient foraging that are highly seasonal and temporally limited, showing a preference for relatively high soil moisture and a short grass sward interspersed with bare and litter‐covered ground (Sim et al 2013, Barras et al 2020). The earlier onset of vegetation growth and reduction in soil moisture induced by warmer ambient temperatures, as well as more frequent droughts, may indeed drastically reduce the availability of belowground invertebrates (Peach et al 2004, Pearce‐Higgins 2010).…”

Predictive models of distribution and abundance of a threatened mountain species show that impacts of climate change overrule those of land use change

“…atmospheric) nitrogen inputs, favouring fast-growing nutrienttolerant plant species (Andrey et al, 2014;Britschgi et al, 2006;Tasser & Tappeiner, 2002). Since ring ouzel relies on patches of short and sparse ground vegetation to forage (Barras et al, 2020;Burfield, 2002), high-productivity grasslands are usually avoided (Buchanan et al, 2003;von dem Bussche et al, 2008). Therefore, it is unknown to which extent these other, parallel changes in land use could also contribute to species' fall, and by extension to the decline of other sympatric mountain species (Knaus et al, 2018;Lehikoinen et al, 2019).…”