Geographical origin of dabbling ducks wintering in Iberia: sex differences and implications for pair formation

Natural and anthropogenic Iberian wetlands in southern Europe are well known for supporting large numbers of migratory Palaearctic waterbirds each winter. However, information on the geographical origin of dabbling ducks overwintering in these wetlands is scarce and mostly limited to data from ringing recoveries. Here, we used intrinsic isotopic markers to determine the geographical origin of male and female Northern Pintails Anas acuta and Eurasian Teal Anas crecca in Extremadura, inland Iberia, a key site for overwintering dabbling ducks. Additionally, we fitted six Northern Pintails with GPS-GSM tags to complement the data derived from stable isotope analysis. Most (>70%) first calendar-year Northern Pintails were assigned to regions above 55 degrees N, flying 2600-5600km from their main natal regions to Extremadura. Mean values of H-2(f) varied significantly between male and female Northern Pintails, suggesting that the sexes had different geographical origins. Data from tagged adult Northern Pintails supported the isotopic data, one male flying more than 5000km to the coast of the Pechora Sea (Russia). Most (>70%) first calendar-year Eurasian Teal were assigned to the region between 48 degrees and 60 degrees N, travelling 1500-4500km to arrive in Extremadura. Male and female Eurasian Teal showed marginal differences in mean values of H-2(f). In migratory dabbling ducks, pairing typically occurs on the wintering grounds, and ducks in their first winter can breed the following spring. For Northern Pintails, pair formation in Extremadura could occur between individuals with different geographical origins, which could contribute to the genetic variability of their offspring.