Snow cover phenology is the main driver of foraging habitat selection for a high-alpine passerine during breeding: implications for species persistence in the face of climate change

Abstract

High-alpine ecosystems are strongly seasonal and adverse environments. In these ecosystems, the brevity of optimal breeding conditions means species must efficiently track spatiotemporal variations in resources in order to synchronise their reproductive effort with peaks in food availability. Understanding the details of prey-habitat associations and their seasonality in such ecosystems is thus key for deciphering species' ecological niches and developing sound conservation action. However, the ecological requirements of high-alpine avifauna remain poorly documented. Furthermore, mountain ranges in the Old World are affected not only by profound alterations of climate, but also by changes in land-use, the interaction of which hampers both proper forecasting of species' resilience to environmental change and delivery of evidence-based conservation guidance. Here, we investigate the prey-habitat associations of a high-alpine passerine, the White-winged Snowfinch (Montifringilla nivalis), by radio-tracking breeding adults in the Swiss Alps. In late spring and early summer, Snowfinches foraged preferentially next to invertebrate-rich, melting snow patches where Tipulidae larvae abound. Later, in mid-summer, they favoured flower-rich alpine meadows. When foraging, they always preferred short ground vegetation while avoiding rock and scree. Their pattern of foraging habitat selection reflects trade-offs between food abundance and accessibility, i.e. prey availability. The reliance of this passerine on a habitat mosaic where snow plays a major role questions its ability to cope with climate change due to future habitat loss and potential phenological mismatches. Targeted grazing could possibly help in habitat management by aiming at maintaining invertebraterich meadows with short vegetation. Yet, it remains an open question whether habitat management would suffice to compensate for the potentially detrimental effects of the progressive retreat of snow fields to higher elevations.

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

“…The selection for intermediate levels of accessible ground, as provided here by patches of bare soil surfaces and vegetation litter, underlines the importance of small-scale substrate heterogeneity in the foraging microhabitat. Similar requirements were evidenced for a variety of ground-foraging, insectivorous farmland birds (Atkinson et al 2004, Schaub et al 2010 but also for some alpine specialists such as the Whitewinged Snowfinch Montifringilla nivalis (Brambilla et al 2017, Resano-Mayor et al 2019. The preference for a heterogeneous microhabitat mosaic has already been demonstrated for foraging Ring Ouzels in the UK (Burfield 2002, Sim et al 2013.…”

“…, Resano‐Mayor et al . ). This is of paramount importance in highly seasonal environments such as temperate mountain ecosystems, where birds are expected to be particularly vulnerable to changes in vegetation phenology (Inouye et al .…”

“…The harsh environment and remoteness of high-elevation ecosystems have hampered fine-grained empirical studies in the past (Chamberlain et al 2012), although such studies represent an absolute prerequisite for meaningful predictions of future distributions (Chamberlain et al 2016) and ought to serve as the basis for conservation management at the local scale (Morris et al 2001. In addition to high spatial resolution, information should also be collected at a fine temporal resolution, such that seasonal patterns of habitat selection can be assessed (Brambilla et al 2017, Resano-Mayor et al 2019. This is of paramount importance in highly seasonal environments such as temperate mountain ecosystems, where birds are expected to be particularly vulnerable to changes in vegetation phenology (Inouye et al 2000) but where very few asynchronies have actually been documented .…”

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).…”

“…Earlier and more extensive snow melt may reveal larger areas of suitable breeding and foraging habitats at higher altitudes (Anderson et al, 2015; Martin & Wiebe, 2004), yet a longer plant growing season may encourage the development of taller mountain vegetation (Ernakovich et al, 2014; Jonas, Rixen, Sturm, & Stoeckli, 2008), reducing the suitability of these areas for species that favour shorter swards (Resano‐Mayor et al, 2019). Furthermore, melting snow patches can offer rich foraging opportunities for alpine birds (Antor, 1995), but a decrease in snow cover and duration may both diminish the overall abundance of these patches, and also desynchronize the timing of resource availability and breeding activity (Resano‐Mayor et al, 2019). Moreover, another potential ecological impact of climate change on breeding birds in alpine areas is via effects of elevated late summer temperatures on invertebrate prey availability.…”