Population Size and Distribution of Chubut Steamer-Duck (Tachyeres leucocephalus) in Patagonia, Argentina.

AGÜERO, M.LAURA; GARCÍA BORBOROGLU, PABLO

Quebec, CANADA

Congreso; Third North American Seaduck Conference.; 2008

Environment Canada (Canadian Wildlife Service and Science & Technology, Québec Region) and Regroupement Québec Oiseaux

Chubut Steamer-Duck Tachyeres leucocephalus is a flightless species endemic of the Central Patagonia marine coast, Argentina. We present the first reliable population size estimate, a critical need for setting conservation priorities. From 2004 to 2007, surveys were conducted along 412 km of mainland coast and 87 km of island coast in the Chubut Province, encompassing its main breeding area. Mid season direct counts of breeding pairs, lone ducks and subadults were performed. To determine the best census technique we conducted boat and ground counts along 36 km of coast, and calculated correction factors by categories and census methods to obtain more accurate population estimation. The global detectability of boat census was 19% higher than ground census. However, detectability differed among categories: boat census detected 70% and 75% more pairs and males, respectively, while ground census detected 9% and 5% more females and subadults, respectively. Hence, boat census are recommended applying this appropriate correction factors. We extrapolated calculated densities to not surveyed sectors. Survey data were used to generate a distribution map using GIS. Total population size for the Chubut Province would not exceed 4700 individuals, with 33% (1565) represented by adults (pairs and lone ducks). Within Chubut Province, the breeding distribution ranges, at least, from Rawson to near Santa Cruz Province boundary. The 62.9% of the total population is located at Northern of San Jorge Gulf, with three main concentration areas: Bahía Melo (31.2%), Bahía Bustamante/Caleta Malaspina (18.1%) and Bahía Camarones/Cabo Dos Bahías (13.6%). Southwards there are reports of very few individuals. Results from our study are currently the only systematic estimate of Chubut Steamer-Duck abundance. This has a multitude of implications regarding management strategies, habitat management goals and research objectives. A regular monitoring scheme should be applied to assess the population growth trend of this unique seaduck species.