Density, abundance, and activity of the chilla or grey fox (Lycalopex griseus) in Isla Grande de Tierra del Fuego, Chile

Abstract Background The chilla or grey fox (Lycalopex griseus) is a native species from continental Chile and neighboring areas of Argentina. It was introduced to Isla Grande de Tierra del Fuego in 1951 and began to increase its abundance, to the chagrin of local sheep ranchers. Since 1998, its hunting has been authorized. Here we update information on the density, abundance, and activity of this fox in the Chilean sector of Tierra del Fuego Island, to evaluate its population trend since the last census conducted by the Servicio Agrícola y Ganadero (SAG) in 2007. Methods and results We carried out two fox censuses on a 941-km transect on public roads, divided into eight routes, from October to November (spring) of 2021 and 2022, following the same design used by SAG for the fox assessments carried out from 1999 to 2007. We report a reduction of > 50% in the density and abundance of chilla foxes with respect to the 2007 estimate, which could be attributed to the interference by free-ranging dogs (Canis lupus familiaris), through restricting the use of space by the fox, while transmitting diseases and parasites, and to human hunting pressure and vehicle collisions. Discussion The chilla fox decline highlights the need for an in-depth study to determine the ecological and socioeconomic impact of this exotic species on the ecosystems of Tierra del Fuego Island and the desirability of its management, if needed.

Kimelfe