Contrasting elevation-dependent effect of snow cover on nest-box use in a cold-adapted alpine specialist, the white-winged snowfinch Montifringilla nivalis

Snow cover plays a critical role for many alpine animals, but our understanding of how snow effects vary with elevation is limited. The white-winged snowfinch is restricted to high-elevation habitats, relying on snowfields, edges of melting snow patches, and short-sward alpine grasslands to collect invertebrates for nestlings. To explore potential elevation-dependent snow effects on breeding occurrence, we monitored 37 nest-boxes in central Italian Alps from 2017 to 2025 (210 nest-box–year combinations in total). Nest-boxes were deployed from 2300 to 3010 m a.s.l., thus encompassing continuous alpine grassland, mosaics of scattered alpine grassland and rocky habitats, and landscapes dominated by rocks and snowfields. Average percentage snow cover was estimated (using remote sensing data) within a 300 m radius around each nest-box during June (peak of breeding activity), and was used to model nest-box use at different elevations. June snow cover varied greatly between years (average 5–64%) and influenced nest-box use in a complex manner. At low elevation (< 2487 m a.s.l.), usage increased with snow cover, whereas it decreased with snow cover at higher elevation (> 2753 m a.s.l.), and was apparently unrelated to snow cover at intermediate ones. At low elevation, increased snow cover means more suitable foraging habitats, including snow patches and the melting margins, as well as short-sward grassland (the most exploited foraging habitat by breeding snowfinches). At higher elevations, nest-boxes tended to be occupied more frequently with relatively limited snow cover. Reduced snow cover here implies more suitable short-sward grassland available to foraging snowfinches, and therefore more profitable conditions. However, above 2900 m a.s.l., nest-boxes were used only thrice and with high snow cover. There, snowfinches probably rely on wind-blown arthropods deposited on snowfields, requiring substantial snow cover. The elevation-dependent patterns we found provide examples of the possible reasons for complex distribution shifts in response to climate change and deserve more investigation.