Morphological description of the White-throated treerunner (Pygarrhichas albogularis, King 1831) in the Cape Horn Biosphere Reserve, Chile

Abstract

The sub-Antarctic Magellanic ecoregion is one of the most pristine wilderness areas remaining on the planet, and is home to the southernmost forest ecosystems in the world, which are protected by the Cape Horn Biosphere Reserve (CHBR). In these forests, birds are the group of vertebrates with the largest number of species. However, essential aspects of the ecology and morphology of several species in this region are still understudied. These species include the White-throated treerunner (Pygarrhichas albogularis, King 1831), considered a “living fossil” as it is the only living species of the genus Pygarrhichas. In addition, this Furnariid is endemic to the temperate forests of South America. Using the 23-year database of the Long-Term Ornithological Research Program of Omora Park (54º56’S, 67º38’W), based on monthly captures and banding of forest birds, we describe the morphology, longevity, and presence of the White- throated treerunner in the CHBR. Between 2000 and 2022, 91 individuals were captured, including 29 recaptures. Based on these recaptures we determined that this species can live for at least five years. Morphometric measures showed a positive correlation between bill measures and tarsus length with both tail and wing lengths. The average weight varied for each season but not significantly. The greater presence on old-growth forests sites suggests a dependence of treerunners on large trees. This study expands the knowledge about the natural history of the White-throated treerunner, particularly about its populations inhabiting the world’s southernmost forests