At various times has been considered to include any or all of H. ater bachmani, H. palliatus, †H. meadewaldoi, H. moquini, H. longirostris, H. chathamensis and H. unicolor. Taxonomic status of form finschi unclear, and may be a distinct species: has frequently been lumped with H. longirostris, or occasionally H. unicolor, or even linked with H. chathamensis; has hybridized repeatedly with H. unicolor#R. Race osculans may also deserve treatment as separate species, and has been treated as such, although without explanation#R; specimen evidence appears not to support a split. Proposed races malacophaga (Iceland and Faeroes), occidentalis (British Is) and buturlini (Turkmenistan and S Kazakhstan) are probably insufficiently distinct to warrant recognition. Has been suggested that populations as far W as NW Adriatic pertain to race longipes#R. Four subspecies normally recognized.
Food and feeding
Status and conservation
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