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The regional population of Damara Tern Sterna balaenarum satisfies the criterion for regionally Critically Endangered under the population-size criterion (population size estimated to number less than 250 mature individuals and an estimated continuing decline of at least 25% within one generation).
The species occurs in Angola, Namibia and South Africa (Crawford and Simmons 1997) with maximum densities occurring in the Walvis Bay region, Namibia, and decreasing uniformly to the north and south of this coastal town (Simmons et al. 1998). Distribution extends c. 150 km north into Angola, although only one breeding colony has been located 30 km north of the Cunene River (Simmons et al. 2010). During autumn migration, the majority of the population is distributed in West Africa, including Benin and Ghana, with Namibian ringed birds being recovered in Nigeria. Within the region, the species is traditionally confined to just 12 breeding localities from Alexander Bay, Northern Cape, to the Alexandria Dune Fields in Eastern Cape, but some are no longer used (Braby et al. 2011). The species is uncommon in South Africa, with perhaps the largest concentration occurring in the Alexandria Dune Fields, east of Port Elizabeth (Braby et al. 2011, Crawford et al. 2012). Coastal distribution is probably related to small-fish availability as much as it is to breeding habitat, because higher densities of breeding terns occur where the greatest offshore productivity occurs (Simmons and Cordes 2000). The Damara Tern is found at five IBAs namely Orange River Mouth Wetlands (SA030), Woody Cape Section: Addo Elephant National Park (SA094), Overberg Wheatbelt (SA115), De Hoop Nature Reserve (SA119) and Heuningnes River and Estuary System (SA121).
The global population is estimated at 14 000 individuals, roughly equivalent to 9 300 mature individuals (BirdLife International 2014), although there is considerable variation in published estimates with several ranging from 930 pairs to 13 500 individuals (Simmons et al. 1998). A global estimate from 2011, which considered only breeding colonies, estimated between 1 001 and 2 685 pairs or 2 002 to 5 370 mature individuals (Braby 2011). Estimates differ due to different methods used (counting at colonies to random sampling across the entire range in Namibia). Within South Africa, Underhill (2000) estimated 120-150 breeding pairs, although, according to Crawford et al. (2012), this figure may have been optimistic. In 2011, Braby estimated there to be 52-88 pairs based on past and present counts and summations at active colonies in South Africa (Braby 2011). However, Crawford et al. (2012) provided a lower estimate of c. 36 pairs breeding in the region based upon 4-11 pairs breeding at De Mond Reserve in Western Cape, and 25 pairs breeding in Eastern Cape (Crawford et al. 2009). Confidence in this latter regional population estimate is high.
The global population is suspected to be stable (BirdLife International 2014), However, disappearance of colonies along the central Namibian coast due to housing developments, and threats from off-road driving (Braby 2011) and diamond mining (Simmons 2005), mean that a slow decline is likely. This is reflected in South Africa where a once thriving colony at Struis Bay (11-13 pairs in the early 2000s) has declined to 1-5 pairs by 2010 (N Hess pers. comm., J Huiseman pers. comm.), while a colony described in the 1990s as ‘sporadic and up to 20 pairs' (Braby 2011) at Dreyer's Pan, Kleinzee area, holds no birds presently (S Sutherland pers. comm., RE Simmons pers. obs.). This parallels the findings of Crawford et al. (2012) whose surveys in 2009-11 revealed only 36 pairs. Even accounting for a possible overestimation of population size by Underhill (2000), the decrease in the regional population has been substantial. An estimated, continuing decline of greater than 25% has likely occurred over three generations. Confidence in this trend estimate is medium.
Off-road vehicle disturbance (leading to nest desertion), and direct fatalities due to crushed eggs and chicks, are the biggest threats to Damara Tern colonies (Braby et al. 2009). The banning of off-road vehicles on South African beaches has reduced such disturbance and increased breeding success (Williams et al. 2004). Semi-natural threats, such as increased jackal and gull densities due to human presence and the increasing numbers of seals and seal colonies in South Africa and Namibia, increase the likelihood of predation (Braby 2011). Natural threats to the terns, and other fish-eating species, come from possible consequences of global warming which may reduce winds driving the Benguela upwelling in turn affecting primary productivity and fish populations available to all marine species. The level of this threat is, however, hard to gauge. It may, conversely, bring increased El Niño oscillations and higher productivity to the Benguela system. Sand-swamping of eggs is the major cause of mortality in the Struis Bay colony (AJ Williams unpubl. data). The spread of non-indigenous, invasive vegetation may have affected some breeding sites in Western Cape (J Cooper pers. comm.)
In South Africa, the Department of Environmental Affairs banned off-road vehicles from all beaches in 2001, which had an immediate positive effect on shorebirds in South Africa (Williams et al. 2004). Protection from vehicles had a similar effect on productivity in Namibia (Braby et al. 2009).
A Population and Habitat Viability Assessment (PHVA) and Biodiversity Management Plan, culminating in a National Species Recovery Plan are recommended. Monitoring of populations needs to be undertaken and published. Given that disturbance and mining are probably the biggest source of mortality and colony abandonment, vigilance in keeping colonies undisturbed, and protecting them formally, are priorities for the few colonies remaining in South Africa.
* Reasons for abandonment of breeding sites, such as the colony at Dreyer's Pan near Kleinzee and the well-monitored colony at Struis Bay, should be researched.
* Studies on diet composition and linkages withrelevant fish populations need to be undertaken.
* Assess population fluctuations in relation to oceanic upwelling and El Niño Southern Oscillation events.