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.  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.