Spatial and temporal dynamics of bird assemblages in the sub-Antarctic forests of the Cape Horn Biosphere Reserve, Chile

Background/Question/Methods

The UNESCO Cape Horn Biosphere Reserve (CHBR) at the austral end of the Americas hosts the world’s southernmost forests. Dominated by the evergreen broadleaf Nothofagus betuloides, the sub-Antarctic forests in Cape Horn also include deciduous patches of N. pumilio and N. antarctica, as well as a mosaic of moorland, high-Andean, coastal, and wetland habitats embedded in a landscape of archipelagoes, fjords, and channels. Sub-Antarctic birds have been described to show island characteristics and have a long time of evolution in isolation from those of other forests. Using 12 years of standardized monthly mist netting at the Omora Ethnobotanical Park on Navarino Island (55^oS), combined with bird censuses in summer and late fall/winter at 61 sites broadly distributed throughout the CHBR, we described (a) the yearly abundance of forest birds and (b) their migratory and distribution patterns. We hypothesize that a great fraction of the forest birds are migratory and that those living in the more exposed western part are more prone to move out in winter. 

Results/Conclusions

A total of 8,778 birds belonging to 24 species were captured with mist-nets. Nineteen species (79%) were passerines and other small forest birds. The House Sparrow (Passer domesticus) was the only exotic passerine, and 4 other were large-size forest birds captured accidently. Three species (Phrygilus patagonicus, Aphrastura spinicauda, and Elaenia albiceps) accounted for 75% of all captures, and 8 species for >95% of the captured birds.  In the CHBR 14 species were residents, 3 partial migrants and 7 Austral migrants. During winter the sub-Antarctic forests retain 58.3% of the bird species. We detected 3 partially migratory species. Of the 19 species detected on the more exposed islands on the West, 12 were residents, 5 were Austral migrants, and 2 presented only local migrations to sheltered sites. Only 3 species are longer distance migrants. E. albiceps was the only species that showed long-distance migration wintering in tropical forests of South America. All the 8 most abundant species were landscape generalists and were found on sites close to the Pacific Ocean, as well as in the interior islands of the archipelagoes south of Tierra del Fuego. Our results identified interesting contrasts of the seasonal dynamics of sub-Antarctic forest bird assemblages with those reported for the boreal forests.