He made systematic revisions of the taxonomy of the birds of Peru and their relatives in other parts of South America, and in his later years combined this with studies of New World flycatchers, preparing the section on the Tyrannidae for Peter's Check-list of Birds of the World.
Asian Paradise Flycatcher | tyrant | European Pied Flycatcher | Ochre-faced Tody-Flycatcher | Drab-breasted Bamboo Tyrant | Collared Flycatcher | Asian Brown Flycatcher | Willow Flycatcher | Tyrant flycatcher | Red-bellied Paradise Flycatcher | Alder Flycatcher | Willow flycatcher | Tyrant | Tickell's Blue Flycatcher ''Cyornis tickelliae | The Tyrant Father | The Seven Sins: The Tyrant Ascending | Spotted Flycatcher | Rufous-vented Paradise Flycatcher | Old World flycatcher | Narcissus Flycatcher | Humblot's Flycatcher | HMS ''Flycatcher'' | HMS Flycatcher | Hicetas (tyrant of Syracuse) | flycatcher | Chapin's Flycatcher | Apical Flycatcher | Aaron the Tyrant |