Ringing IN THE Changes
African Birdlife|January/February 2022
Sandwich Terns in South Africa
THEUNS KRUGER

Sandwich Terns Thalasseus sandvi-censis are common non-breeding summer visitors found along the entire length of the South African coast, where they are usually seen in the company of Common and Swiftterns as well as gulls. The number of Sandwich Terns that visit South Africa annually is estimated at between 10 000 and 15 000, which equates to less than 10 per cent of the population in western Europe where they breed.

These terns have been ringed in Europe and the British Isles for more than 100 years and rings have been recovered in South Africa from dead and captured birds over many decades. Although they provided useful information relating to the origin and age of the birds, they gave limited insight into the full life history of Sandwich Terns, including how many times and when a specific bird has been to South Africa. This situation has changed drastically over the past few years as a result of changes in ringing practices.

Traditional metal rings used to have codes engraved in small letters around the ring and could only be read with the bird, dead or captured, in the hand. Over the past decade, however, ringers in Europe have been changing over to rings that can be read in the field. The most popular type is the engraved color ring made of plastic and with an alpha or numeric code, usually three letters or digits written vertically on the ring. A variation on this is the coloured flag. Both rings and flags can be read in the field with a telescope or a camera with good zoom capability. Ringers in some countries, such as Germany, Denmark, and Poland, opted to stay with the more durable metal rings but changed the font to large letters or numbers engraved vertically. Their codes consist of six letters or digits arranged in two rows. Although not as easily recognizable and readable as the colour rings with their contrasting ring and letter colours, these metal rings can still be read in the field with the same equipment as the color rings.

At the same time as the colour rings were introduced, protocols for the reporting of ring sightings were streamlined. Traditional metal rings were usually reported through the national ringing organizations and there was no direct contact between the observer and the ringer. In the case of a color ring, the observer can now refer to listings on the internet, obtain the e-mail address of the ringer and report the sighting directly by e-mail. In exchange, he or she receives a full life history of the bird, including the date and place of ringing and all further sightings up to the latest one.

Over the four summer seasons of 2017–2018 to 2020–2021, I have observed ringed Sandwich Terns along the south-western coast from False Bay to Cape Agulhas, concentrating on Strand (Greenway's beach), Macassar (Eerste River mouth), and the Gansbaai area. Over the entire period, I reported 429 individual ringed Sandwich Terns. Multiple sightings of many of these birds amounted to a further 654 records, bringing the reported sightings to 1083.

In several cases a sighting report was the first that the ringing group had received from South Africa, even though it had been ringing terns for many years. This suggests a general lack of awareness of the presence of these rings along the South African coast.

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