Hydroprogne caspia
Records: 35
Drafted by: Faansie Peacock
Draft Text Last Updated: 14 June 2005
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Distribution: Records were obtained from most of the major artificial water impoundments in the study region – in particular, Bronkhorstspruit Dam NR with 8 records (=23%), Borakalalo NP with 7 records (=20%), and Roodekoppies Dam with 6 records (=17%) seem to be important strongholds for this species. However, all the Borakalalo records are from the same date, and probably reflect the same birds. Apart from these 3 sites, they were also recorded at Rust de Winter Dam NR, Vaalkop Dam NR and Diepsloot NR. Two interesting localities are Longside Farm and Suikerbosrand NR, where little habitat is available. These birds are possibly juvniles that tend to wander for long distances (SABAP1:468).
Gaps in Knowledge: Some of the sites (e.g. Bronkhorstspruit Dam, Roodekoppies Dam, Borakalalo NP) support sizeable flocks of Caspian Terns that usually occur annually, and could potentially host breeding colonies. Although there were no reports of breeding activities, this species should be monitored during the winter months when breeding occurs on sandbanks exposed by lower water levels. In the event that a colony is established, sensitive management will be needed – breeding birds are highly intolerant of disturbances (Barnes 2000). Participants should always include the number of birds seen with this species.
Habitat: Normally associated with large waterbodies where relatively large fish prey (mostly 9 -25 cm, 10-40g) is common (Barnes 2000). Often seen perched on sandbars or mudbanks, which are also used for breeding. In summer months, the inland populations of Capsian Terns are speculated to switch to coastal and esuarine habitats (SABAP1:468).
Status and movements: This species was observed from 5 May to 6 January, but the vast majority of records was in mid-winter to spring. The months June – August were responsible for 49% of the 35 records, while June – September included 71% of all the records.It is thought that birds that spend the winter months at inland waterbodies, travel to the coast, where they forage in coastal and estuarine habitats during the summer months, when high water levels inundate inland sandbars. Such a pattern is supported by the data, in that birds depart from their winter locations when the first major rains causes a rise in water levels. Records after November are probably of wandering juveniles or adults en route to alternative habitats.
Population: Can be locally common, often forming sizeable flocks on roosting islands. P. Tyler reported 20 birds from Bronkhorstspruit Dam NR on 26 May 2003. The next year this figure decreased to 11 birds on 18 July 2004 (A. Marx), while 16 birds were present at Borakalalo NP on 12 September 2004 (E. Marais).
Prior to the study period, 55 birds were recorded at Bronkhorstspruit dam on 6 August 2001 (pers. obs).
Conservation: Listed as Near-Threatened. Chemical pollutants such as heavy metals and pesticides accumulate through the various trophic levels, resulting in a buildup of these elements in carnivorous animals. The Caspian Tern’s preference for relatively large fish makes it particularly vulnerable to this process, the effects of which will precipitate in areas such as eggshell thickness. Other threats (that are related to breeding colonies) are discussed in the Eskom Red Data Book of Birds of South Africa, Lesotho and Swaziland (Barnes 2000).