The South American subspecies of Black Skimmer, Rynchops niger intercedens, is an important neotropical bird, widely distributed from Venezuela to the southeastern coast of Argentina. Population information for this subspecies is scarce and restricted to local distribution sites, making their conservation status difficult to determine. In Argentina, anecdotal information on breeding grounds suggest small colonies of R. niger intercedens next to rivers, contrasting with the high numbers registered on non-breeding grounds on the southeastern coast of Argentina (up to 10,000 non-breeders in Mar Chiquita Coastal Lagoon). This observed contrast in bird abundances raises the question of the existence of a non-breeding mixture of birds from breeding colonies distributed throughout the main South American hydrological basins. In this study researchers analyzed the genetic differences between skimmers’ populations from Brazil and Argentina, sampling individuals at breeding sites in Brazil and Argentina, and the large non-breeding site at Mar Chiquita (Argentina).
Microsatellite DNA analysis was used to detect significant genetic differentiation between sampling sites, providing evidence that South American populations of the black skimmer are not completely panmictic (mating randomly across the entire distribution). Moreover, results suggest the existence of at least two genetic groups, one formed by the Brazilian population and another including the Argentine sites. Higher genetic diversity was observed in the Mar Chiquita population, supporting the hypothesis of this site as a converging wintering area for multiple skimmer groups. In fact, 20% percent of the samples from Mar Chiquita could not be assigned to either the Brazilian or Argentine breeding colonies, suggesting the existence of additional breeding colonies that migrate to Mar Chiquita. Based on the molecular analyses from this study, the populations from Brazil and Argentina should be managed separately and protected as independent populations. Ongoing studies including additional colonies will reinforce these results. Mar Chiquita should also be considered a key wintering/stopover area where several populations of skimmers seem to be converging, comprising a critical site for the conservation and management of this species. ($9,000)