Abstract
ABSTRACT
Understanding the dietary flexibility of migratory birds is essential for predicting their resilience to rapid environmental changes. For the continental black‐tailed godwit (
Limosa limosa limosa
), precise knowledge of seasonal diets and the underlying causes of prey selection on their breeding grounds has remained limited. This is largely due to challenges of observing foraging in tall vegetation and the rapid digestion of soft‐bodied prey. We utilized DNA metabarcoding of 207 fecal samples to describe the diet of flock‐foraging godwits in southwest Friesland, the Netherlands, during pre‐nesting (March) and post‐nesting (May–June) periods. To assess whether dietary changes were resource or selectivity based, we simultaneously quantified soil macrofauna biomass and measured biophysical variables, including soil moisture content, soil penetration resistance, and vegetation height. Earthworms (Lumbricidae) and leatherjackets (Tipulidae) were the primary prey taxa detected. A significant dietary taxa shift occurred between periods: earthworm relative read abundance (RRA) dropped from 73% pre‐nesting to 21% post‐nesting, while that of leatherjackets increased from 3% to 47%. While earthworms were consumed in proportion to their soil biomass in March, their selectivity declined significantly in May and June as soils became drier and harder. Conversely, leatherjacket consumption was higher in the post‐nesting period as their individual biomass increased. Our results demonstrate that the seasonal shift in godwit diet is caused by an interaction between prey life cycles and habitat conditions that impact prey harvestability. Soil desiccation post‐nesting reduces the detectability and accessibility of earthworms, even when they remain present in the soil, potentially forcing birds to switch to leatherjackets as they become more profitable. As climate change and intensive land use exacerbate soil drying in agricultural grasslands, the window for godwits to access earthworms is narrowing. This study highlights that maintaining high soil moisture is critical not just for prey abundance, but to ensure food remains accessible to meadow birds during the vital fueling period before southbound migration.