Birds that specialize in feeding on nectar, such as hummingbirds and sunbirds, often have long, slender beaks while the ones that feed on insects may have long, thin beaks that help them probe into crevices or vegetation to extract insects or larvae. Some birds have longer, stout beaks that are adapted for cracking open tough seeds or fruit. Certain waterbirds, such as flamingos and some ducks, have elongated beaks with specialized structures that aid in filter-feeding.