Gabriel Rojo / Cattle tyrant (Machetornis rixosus) perched on capibara (Hydrochoerus hydrochaeris) Ibera Marshes, Corrientes Province, Argentina

Gabriel Rojo / Marsh deer (Blastocerus dichotomus) male with Cattle tyrant (Machetornis rixosus) on back, Ibera Marshes, Corrientes Province, Argentina.

Patricio Robles Gil / Silhouetted Capivara / Capibara (Hydrochoerus hydrochaeris) with Cattle Tyrant (Machetornis rixosa), which feeds on flies approaching the Capibara. Parana, Southern Brazil.

Konrad Wothe / Cattle Tyrant (Machetornis rixosa) on Capybara (Hydrochoerus hydrochaeris), Pantanal, Brazil

Gabriel Rojo / Marsh deer (Blastocerus dichotomus) male with Cattle tyrant (Machetornis rixosus) Ibera Marshes, Corrientes Province, Argentina

Thomas Marent / Cattle Tyrant (Machetornis rixosa), Guajira Peninsula, Colombia

Gabriel Rojo / Fork-tailed flycatcher (Tyrannus savana) sitting on wire fence in front of Domestic cow, La Pampa, Argentina

Tony Heald / Cattle tyrant (Machetornis rixosa) stretching wing, Pantanal, Brazil

Tony Heald / Capybara (Hydrochoerus hydrochaeris) female with young, also with Cattle tyrant (Machetornis rixosa) on her back, Pantanal, Brazil

Ben Cranke / Wattled Jacana (Jacana jacana), Cattle Tyrant (Machetornis rixosa) on Capybara (Hydrochoerus hydrochaeris) Mato Grosso, Pantanal, Brazil. July.

Ben Cranke / Cattle Tyrant (Machetornis rixosa) perched Capybara (Hydrochoerus hydrochaeris), Mato Grosso, Pantanal, Brazil. July.

Angelo Gandolfi / Cattle Tyrant (Machetornis rixosa) Pantanal, Brazil