Aspects of the diet and nesting of the Black-billed Shrike- tyrant, Agriornis montanus (Tyrannidae: Passeriformes), in the Andean region of Mendoza province, Argentina

Abstract

Agriornis montanus, or the Black-billed Shrike-tyrant, is a bird belonging to the Tyrannidae family with a wide distribution in the Andean region of Argentina, especially in the province of Mendoza, where the subspecies A. m. maritimus is found. This bird, distinctive in size and appearance, has a strong beak adapted to capture a variety of prey, including insects, rodents, small vertebrates, seeds, and even waste. It inhabits a broad range of environments in Mendoza, from rocky steppes to high-altitude grasslands, and makes altitudinal movements during severe winters. Its behavior is discreet, with vocalizations similar to human whistles, and it is well known for its confidence and proximity to persons and settlements. During the nesting season, it builds nests in crevices, rocks, or antropic structures, using vegetation and soft materials such as wool. The nests are typically located on ledges and usually contain two or three white eggs with spots. Between 2010 and 2020, observations were made in various protected natural areas and their buffer zones, documenting its predatory behavior, dietary items, and some aspects of its nesting activity. A. montanus is considered a key species in the Andean trophic chain, and although it is not currently threatened, continued research is recommended to better understand its biology and to consider the inclusion of new protected areas that conserve its habitat.