The population dynamics of passerine birds could be strongly influenced by human induced climate change. Annual variation in climatic variables has been shown to impact, for example, their daily activity patterns and food availability, which in turn could a effect the survival and reproduction of birds. During the last two decades, climate conditions have evolved in the sub-Antarctic temperate forests of South America, mainly because of the climatic phenomenons El Nino and La Nina. Nevertheless, only a few long-term monitoring studies have been made in this regions on the effect of climate variables on the dynamics of bird populations. Hence, my study analyses the monthly evolution of two passerines populations, the Patagonian Sierra-Finch (Phrygilus patagonicus) and the Thorn-tailed Rayadito (Aphrastura spinicauda) over the last 20 years on the Omora Ethnobotanical Park of the Cape Horn Biosphere Reserve, Navarino Island, in Chile. The effect of monthly average temperature, precipitations and snow coverage on these populations has also been investigated. Generalized Additive Models were used to explore the non-linear relationship between climatic and temporal variables with the abundance of birds. This study shows an abundance decrease of almost 75% for both bird species over the last 20 years and a significant positive effect of rain on the abundance of the Thorn-tailed Rayadito. This abundance decrease is potentially due to the increased abundance of newly introduced predators on Navarino Island, such as the American Mink (Neovison vison), which can be a concrete danger for these passerine populations. Understanding the populations dynamics of passerine birds over the last years and the influence of climatic variables may help to build protection plans for the species threatened by climate change.