Cocos Tyrannulet Nesotriccus ridgwayi is embedded within the genus Phaeomyias (Zucker et al. 2016, Harvey et al. 2020); as Nesotriccus Townsend 1895 has priority over Phaeomyias Berlepsch 1902, Phaemomyias is considered to be a junior synonym of Nesotriccus. The presence of Cocos Tyrannulet within Mouse-colored Tyrannulet thus makes the latter to be paraphyletic; furthermore, the vocalizations of several taxa previously considered to be subspecies of Mouse-colored Tyrannulet are rather different (Ridgely and Greenfield 2001, Schulenberg et al. 2007, Boesman 2016j). Therefore Mouse-colored Tyrannulet is split into four species: the polytypic group Mouse-colored Tyrannulet (Tumbes) Phaeomyias murina tumbezana/inflava becomes Tumbes Tyrannulet Nesotriccus tumbezana, with subspecies tumbezana and inflava (Because the name Nesotriccus is masculine, while Phaeomyias is feminine, the correct formulations are Nesotriccus tumbezanus, with subspecies inflavus; we became aware of this mistake too late to correct in the eBird/Clements spreadsheet, but we will revise the name accordingly in our 2023 release; the monotypic group Mouse-colored Tyrannulet (Marañon) Phaeomyias murina maranonica becomes Marañon Tyrannulet Nesotriccus maranonica (for which the correct formulation is Nesotriccus maranonicus); the polytypic group Mouse-colored Tyrannulet (Northern) Phaeomyias murina incomta/eremonoma becomes Northern Mouse-colored Tyrannulet Nesotriccus incomta, with subspecies eremonoma and incomta (for which the correct formulations are Nesotriccus incomtus, with subspecies eremonomus); and the polytypic group Mouse-colored Tyrannulet (Amazonian) Phaeomyias murina murina/wagae becomes Southern Mouse-colored Tyrannulet Nesotriccus murina, with subspecies wagae and murina (for which the correct formulation is Nesotriccus murinus; but the name wagae is invariant).