Closely related to L. argentatus, and in past sometimes considered conspecific, but in most areas of sympatry the two are reproductively isolated; molecular evidence separates present species from L. argentatus and L. cachinnans. Very complex systematics involving several of the races. Some evidence that heuglini overlaps nominate fuscus in range, perhaps without interbreeding; may merit specific status as L. heuglini, which may even include form vegae (currently treated as a subspecies of L. smithsonianus). Form barabensis has been treated as a race variously of present species, of L. argentatus, of L. cachinnans and of L. heuglini (when last-mentioned treated as a separate species), or as a separate species, L. barabensis, or considered to be a hybrid form not worthy of recognition at all (despite distinctive characters). Described form antelius (from W Siberia) is regarded as a synonym of heuglini; proposed form taimyrensis (Yenisey and Taymyr Peninsula) often considered inseparable from heuglini and, pending further molecular study#R, this position taken here. (See also L. argentatus, below). Five subspecies currently recognized.
Food and feeding
Status and conservation
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