The taxonomy of this group is confusing. The larger and far more widespread Sick's Swift was previously regarded as a subspecies of the Ashy-tailed Swift, but Marín (1997) found that Sick's Swift was closer to the Chimney Swift. Marín further suggested that the Ashy-tailed Swift was identical to Vaux's Swift of the subspecies aphanes. If following this approach, andrei (with aphanes as a junior synonym) becomes a subspecies of Vaux's Swift. This, however, is considered mistaken by Restall et al. (2006), where it is mentioned that they, while virtually identical under normal field conditions, actually do differ and also have different behavior and habitat preferences (Ashy-tailed Swift prefers forested lowland rivers, while Vaux's Swift race aphanes prefers mountain slopes).