What primary food source do whimbrels seek using deep probing in soft substrates?

Marine invertebrates such as crabs, marine worms, and mollusks

The long, specialized bill of the whimbrel has evolved specifically for foraging in soft substrates like mudflats and sandy shores. Their primary sustenance, particularly when they are staging during migration along coasts, consists of marine invertebrates. This diet heavily features creatures such as crabs, various marine worms, and mollusks which are often buried beneath the surface sediment. This structure allows them to employ tactile feeding, probing deep into the sand or mud and sensing for prey without needing direct visual contact. While they adapt their diet on breeding grounds to include insects and eggs, their reliance on deeply buried marine life during migration is critical.