Justification of Red List Category
A more recent comprehensive review of the species's population status estimates the global population to number up to 5,730 breeding individuals (Braby 2011). The continuing demand on Namibia’s beaches (holding 87-93% of the population) by off-road vehicles, the diamond mining and the residential development is currently impacting the population and will likely continue in the future. Based on the estimated population size of <10,000 mature individuals, which is suspected to be undergoing a continuing population decline, this species has been listed as Vulnerable.
The population is estimated at 2002-5370 mature individuals, roughly equating to 9000 individuals in total.
The continuing demand on Namibia’s beaches (holding 87-93% of the population) by off-road vehicles, diamond mining and residential development is currently impacting the population (with three colonies extinct and six declining) and will probably impact most colonies in the future.
Sternula balaenarum is recorded in the breeding season along the coast of Namibia (87-93% of the population nest between the Orange and Cunene rivers [Braby 2011]), south to the Cape provinces in South Africa (65-148 pairs [Braby 2011], although some estimates are as low as 36 breeding pairs) and north to Cabinda in Angola (Gochfeld and Burger 1996), where there are fewer than 190 pairs (Simmons 2010). A recent survey between Tombua and the Cunene River mouth (197 km) recorded 573 individuals, with a breeding colony (6 pairs) located 30 km north of the Cunene River (Simmons 2010). It disperses north after the breeding season and is recorded regularly from the coastal waters of Democratic Republic of Congo, Congo, Gabon, Cameroon, Nigeria, Benin, Togo, Ghana and Côte d'Ivoire (Urban et al. 1986, Demey and Fishpool 1991, Gochfeld and Burger 1996, Braby 2010). In 2011, a comprehensive review was conducted of all existing monitoring data of breeding Damara Terns in South Africa, Namibia and Angola (Braby 2011). A total of 70 breeding colonies were recorded, of which breeding individuals ranged between 2002 and 5370 (Braby 2011). Damara Terns showed high fidelity to their breeding sites (Braby et al. 2012). The peak breeding density is found in the central area of its range (around 23°S) - apparently the main spawning ground of many fish species - and decreasing density north and south along Namibia's 1,470 km coast (Simmons et al. 1998).
Behaviour This species is a partial migrant (Urban et al. 1986). It breeds between late October and March, with records of breeding up to June, in small groups usually consisting of less than 40 pairs (Braby 2011). Pre-migratory flocks of tens, hundreds or occasionally thousands of birds gather at the Namibian coast in April and then move northwards as far as Nigeria and Ghana (del Hoyo et al. 1996, Hockey et al. 2005). The species is most numerous here between July and October (del Hoyo et al. 1996), coinciding with the arrival of strong upwellings off the Ghanaian coast which bring spawning fish inshore (Hockey et al. 2005). About 100 individuals remain in the breeding grounds year-round. Outside the breeding season, it roosts colonially, but usually feeds solitarily, with individuals spaced 10-50 m apart (Urban et al. 1986). It returns to its breeding grounds in September and October (Hockey et al. 2005).
Habitat This species is predominantly coastal (Hockey et al. 2005). Breeding It breeds on gravel and stony plains, salt pans and dunes, sometimes in sheltered bays and shallow reefs, but often several kilometres inland (Urban et al. 1986, del Hoyo et al. 1996, Hockey et al. 2005). It will also breed on rocky ledges and at rehabilitated diamond mines, favouring breeding localities that provide good visibility (Harrison et al. 1997). It shuns outer beach areas that are frequented by predators (del Hoyo et al. 1996, Gochfeld and Burger 1996). There are very few records of breeding on islands (Hockey et al. 2005). Non-breeding During the non-breeding season, it is found on more exposed coasts (Hockey et al. 2005). The species usually feeds in the shallow, inshore waters of bays, estuaries, lagoons and salt-pans and in the surf zone, but occasionally forages in the open ocean, as far as 5 km from land (Urban et al. 1986, del Hoyo et al. 1996, Gochfeld and Burger 1996, Hockey et al. 2005).
Diet It feeds mainly on small fish (usually less than 50 mm in length), including mullet Mugil richardsonii and anchovy Engraulis capensis, as well as small squid (del Hoyo et al. 1996, Hockey et al. 2005, Braby et al. 2011).
Breeding site Eggs are laid in a nondescript scrape, sometimes lined with shell chips or small stones (del Hoyo et al. 1996, Hockey et al. 2005). The clutch-size is usually one, rarely two, and the incubation period is 18-22 days, followed by a fledging period of 20 days and 2.5 months of dependency (del Hoyo et al. 1996).
Apart from disturbing birds, diamond mining causes loss and degradation of habitat, as well as sediment discharge (Braby 2011). This was found to significantly affect feeding success of Damara Terns at a studied colony in Elizabeth Bay in southern Namibia (Braby 2011). The use of off-road vehicles reduces reproductive success by destroying nests and causing stress and disturbance. The banning of off-road vehicles on South African beaches increased breeding success (Williams et al. 2004); a similar ban at Caution Reef increased nesting density and hatching success from 56% to 80% (Braby et al. 2001). High numbers of visitors in Namibia coincide with the peak of the breeding season. Although regulations are in place to protect the birds from disturbance by tourists, they are not well enforced (Braby 2011). Coastal development has caused colony extinctions throughout the species's range (Braby 2011), with future development threatening remaining colonies.
Offal from fishing attracts Black-backed Jackals Canis mesomelas, which have been recorded as the highest cause of chick mortality and nest failure (Braby 2011). Damara Terns are caught and sold to eat in Angola and west African countries (Braby 2011). No information exists regarding the scale of this trade; so the impact on populations is unknown, but it may be causing fluctuations. Future changes associated with climate change could cause flooding of low-lying colonies, such as at Hottentots Bay, and could also cause a flux in food availability due to decreased upwelling and increases in sea surface temperatures (Braby 2011, Roux 2003).
Conservation Actions Underway
CMS Appendix II. In November 2000, information boards and barriers were used to successfully prevent off-road vehicles entering the breeding site at Caution Reef. This resulted in a slightly increased nesting density and enabled hatching success to increase from 56% to 80% (Braby et al. 2001). The banning of off-road vehicles on South African beaches in 2001 reduced disturbance along breeding beaches and increased breeding success (Williams et al. 2004). Similar results were obtained in Namibia by restricting vehicle access over the course of two breeding seasons (Braby et al. 2009).
23 cm. Small, very pale tern. Adult has black cap extending onto nape and very pale grey back. In flight, black triangular wing tip runs from the carpal to primary tip. Non-breeding adult shows white forehead and crown, with black mask extending and joining on nape. Immature has buff barring on mantle. Similar spp. Breeding Little Tern Sterna albifrons has white forehead and mainly yellow bill. In non-breeding, has less white on head, darker mantle and more slight proportions. Voice Sharp, high-pitched tsit tsit and harsh, rapid kid-ick.
Text account compilers
Shutes, S., Stuart, A., Taylor, J., Ashpole, J, Anderson, O., Martin, R., Moreno, R., O'Brien, A., Butchart, S., Palmer-Newton, A., Pilgrim, J.
Simmons, R.E., Hagen , C., Braby, J.
BirdLife International (2019) Species factsheet: Sternula balaenarum. Downloaded from http://www.birdlife.org on 23/09/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 23/09/2019.