Masatierra Petrel Pterodroma defilippiana Scientific name definitions

This account is dedicated in honor to Juan Aguirre Castro (1947-2022), one of the pioneers in the study of the birds of the Desventuradas Islands in Chile, and the description of the natural history of this petrel and several other Chilean birds.

The Masatierra Petrel is part of the Cook’s Petrel assemblage, often referred to as the subgenus Cookilaria, and occurs in the southeastern portion of the Pacific Ocean. This species is differentiated from both the Cook's Petrel (Pterodroma cookii) and the Stejneger's Petrel (Pterodroma longirostris) by the lack of a black tail tip, its stouter bill, and its darker eye patch.

A distinctive attribute of this species relative to the other members of the Cookilaria subgenus is its breeding range, which is confined to only three islands off the coast of Chile: Juan Fernandez (Masatierra) Island, San Ambrosio Island, and San Felix Island, and not in Oceania. Its distribution at sea is limited to the Humboldt Current in Chile and Peru. Presumably, it is highly pelagic, and it likely feeds on marine invertebrates such as squid, but many aspects of its ecology and life history, including its diet and foraging behaviors, require further study. Interestingly, it is one of the few tubenoses to visit its colonies during the day. It is considered Vulnerable due to its extremely small population (estimated at a few thousand), but its trend is stable.

Masatierra Petrel is one of the least known gadfly (Pterodroma) petrels due to the lack of studies that involve tracking. Despite this, in the present account, we have retrieved novel aspects regarding molt, distribution, vocalization, behavior, and breeding.