International assessments suggest that populations of the Black Skimmer are healthy overall. For example, the International Union for the Conservation of Nature classifies the species as being of “least concern” (BirdLi). An earlier assessment of neotropical birds broadly also categorized the Black Skimmer as “low conservation priority”, which was defined as species that have a widespread distribution, are habitat generalists, and/or uses non-threatened habitats so are thus not at risk (Parker et al. 1996). The same assessment considered the species a “medium research priority”, based on the level of knowledge of its life history, distribution, and taxonomy.
Other treatments have offered a different view. Murphy (1936) mentioned a puzzling “apparent great diminution in numbers within the last century or so”. He also noted that the species was less abundant in many areas then, where it had previously been reported as abundant.
More currently, Scherer et al. (2013) stated that “recent studies in North America point to a global decline in Black Skimmer numbers”, such as Foster et al. (2009). Certainly, rampant coastal development in some parts of the distribution are putting pressure on skimmer colonies, such as in Florida (FWC 2013).
Fish-eating birds like skimmers can be useful as bioindicator species of aquatic environments. They rely on small prey, so Black Skimmers do not compete directly with fishermen, but they can indirectly affect mortality of juvenile fish. Thus, trophic relationships involving skimmers could shed light on other components of their ecosystems (Naves and Vooren 2006).
Effects of human activity on populations
To explain observed skimmer declines in South America, Murphy (1936) could think of no reason other than these birds were considered “excellent eating”. This is supported by Preston (1962), who observed human predation in the form of egg collection from a skimmer colony on the Upper Amazon.
Such human take is likely not too widespread. More important is the fact that migratory animals, like skimmers, rely on diverse resources and habitats spread across geographical and political realms. The framework for environmental protection is typically inconsistent across borders, and important habitats may not be protected.
The tracking study of skimmers in the Andes-Amazon region illustrates this perfectly (see Distribution: Dispersal and Migration). Davenport et al. (2016) showed how individual birds are using multiple habitats across different countries, stretching across mountain ranges from Bolivia to Peru, for feeding, breeding and migration. They noted that some of those areas important for skimmers are still privately held despite being declared significant wetlands, and that development plans for the region involves activities that will disrupt wetlands such as more intensive agriculture, dams, mining and forestry. This is concerning because experience with African Skimmer (Rynchops flavirostris) has documented declines since construction of a dam on the Zambezi (Coppinger et al. 1988).
Other potential pressures relate to pollution, climate change, and general modification of coastal habitats. In southern Florida, recent tropical storms have disrupted some skimmer colonies (personal observation), although how this compares to past storm regimes is not clear. The satellite tracking in Peru and Chile showed that stopover sites were all near mouths of freshwater rivers (Davenport et al. 2016); those authors pointed out that most freshwater lagoons along South America’s Pacific coast are heavily altered for agricultural use, while being important to migratory birds (Myers et al. 1987).
A final note is that trophic segregation between the sexes (see Diet and Foraging) - with males being larger and choosing different, larger prey - could have implications for conservation measures. That is, environmental changes that can influence avian life-history traits could affect males and females differently (Mariano-Jelicich et al. 2007, 2008).