Black Skimmer is a relatively common aquatic bird from the southern United States south throughout Central America, and in the bulk of South America except for the sub-Antarctic south, and, as a breeder, the Pacific coast of South America. In the Neotropics it is more closely associated with large rivers, compared to a mainly coastal distribution in North America (Murphy 1936).
Subspecies niger breeds mainly in the eastern and southern coasts of the United States and in Mexico, wintering from Texas and Florida to Panama and Guadeloupe. A smaller population occurs in the west, from southern California into Mexico (Gochfeld and Burger 1994).
The two southern subspecies are strictly Neotropical. Black Skimmer is not known to breed along the coast of northern South America (Murphy 1936). Generally, cinerascens breeds on the coasts and rivers of northern South America (Murphy 1936), from Colombia east to the Guianas, south to Bolivia and Amazonian Brazil. Parker et al. (1996) report Black Skimmer as a breeding species in Panama, which if so presumably would refer to cinerascens; but this may be an error, as breeding in Panama is not reported by Wetmore (1965) nor by Ridgely and Gwynne (1989).
Subspecies intercedens is widely distributed from south central and northeastern Brazil south to central Argentina. Although it is known to breed on large rivers and continental water bodies, the main nonbreeding aggregations are in coastal areas (Zusi 1996)./p>
Dispersal and Migration
Most Neotropical populations of Black Skimmer have post-breeding migrations or dispersal, but these are only now coming into focus. At least occasionally, the distributions of two populations of Black Skimmer overlap as a result of dispersal. For example, both niger and cinerascens have occurred in Panama, usually loafing on sand bars or mud flats with other gulls or terns. Similarly, cinerascens is a common nonbreeding visitor to Trinidad, and niger also may be a visitor to the region (ffrench 1991).
As Mariano-Jelicich and Madrid (2014) summarized, several wintering sites have been described along the southern Atlantic coast (Favero et al. 2001, Branco and Fracasso 2005, Naves and Vooren 2006; Alfaro and Clara 2007; Barbieri 2007) but the most important South American wintering site is located at Mar Chiquita Coastal lagoon in Argentina, with abundances up to 12,000 individuals between late February and May (Ferrero 2001; Mariano-Jelicich et al. 2003). There are also large winter concentrations of skimmers in southern Brazil: Scherer et al. (2013) observed skimmers in both breeding and nonbreeding plumage on a wintering area, suggesting that different breeding populations might gather there from middle eastern Brazil, southern Brazil and Argentina (see Molts). The difference in the size of skimmer aggregations on breeding versus nonbreeding areas suggests that individuals from different breeding areas in South America may migrate and converge in large non-breeding flocks during the austral winter (Mariano-Jelicich and Madrid 2014).
One of the greatest mysteries in Black Skimmer biology has been its status on the Pacific coast of South America. It occurs there regularly, often in large numbers, from southwestern Colombia south to Chile, but breeding on the coast never has been confirmed (Murphy 1936). Murphy (1936) suggested that skimmers on the coast of Peru and Chile "are merely migrants from the river systems to northward and southward"; that Black Skimmer might instead be a trans-Andean migrant apparently did not occur to him, although he was aware of a record from Lake Titicaca, high in the Andes (Allen and Garman 1875). Davenport et al. (2016) noticed that after breeding, large groups of skimmers congregated in November in the Manu region at the base of the Andes in southeastern Peru, where they are not known to breed; they thought this suggested that skimmers might be staging for collective crossings over the Andes (L. C. Davenport and J. Terborgh, personal observations). Data obtained by satellite telemetry supported that hypothesis. Davenport et al. (2016) showed that two skimmers crossed the high Peruvian Andes to the Pacific Coast; both birds crossed in southern Peru, but they followed different routes. Several skimmers made long-distance movements (up to 700 km) between the Manu River and other, remote watersheds, even during the breeding season, and some journeys involved multiple round-trip visits (e.g., to Brazil and Bolivia). Another individual traveled over 1800 km to the southeast before transmissions ended in eastern Paraguay. One of the trans-Andean migrants made a full round-trip migration back to its tagging location after traveling south to spend the austral summer in the Gulf of Arauco, Chile.
These are exciting findings, showing how much remains to be revealed about the movement ecology of Black Skimmers. The authors noted that this represents the first time a bird breeding in lowland Amazonia was shown to migrate across the Andes, and possibly the first example of a tropical-breeding waterbird migrating out of the tropics to spend the non-breeding season in the temperate summer (which is the opposite pattern of seasonality for austral migrants in general; Davenport et al. 2016).