Snowmelt and laying date impact the parental care strategy of a high-Arctic shorebird.

Why parental care strategies can vary from uniparental to biparental care across taxa remains unclear, likely because various sets of ecological conditions are at-play. Here we tested ten possible hypotheses to decipher the direct and indirect impacts of critical factors likely to influence the parental care strategy during incubation in Sanderlings (Calidris alba), one of the few species that uses both types of care during that critical time of the breeding cycle. We examined three ecological factors (timing of local snowmelt, regional temperatures, and the North Atlantic Oscillation experienced just before breeding), one trophic factor (predation pressure), and two social factors (relative abundance of Sanderlings and their laying dates). Using long-term data from Greenland (2011-2023), path analyses revealed that laying date and snowmelt influence parental care strategies during incubation, with indirect climatic effects during migration and on breeding grounds. We observed a greater proportion of uniparental nests in years with delayed laying dates, and the reverse in years with delayed snowmelt. These findings underscore the complex interplay between environmental parameters and parental care strategies, offering insights into how these strategies are likely to respond to rapidly changing Arctic ecological conditions driven by climate change.