From Swakopmund’s sands to Amsterdam’s canals: A Tern’s 8,429-kilometer Odyssey
From Swakopmund's sands to Amsterdam's canals:
A Tern's 8,429-kilometer Odyssey
“…they travel around 20,000 km each year between the Southern and Northern Hemisphere.”
Text Dirk Heinrich | Photographs Dirk Heinrich
From the Winter 2024 issue
I have been out at night at the Swakopmund Salt Works together with Mark Boorman on almost twenty occasions to ring terns between February 2006 and January 2014. During this period, I ringed 326 Common Terns and fitted one of them, an immature bird, with ring 4H39662 on 23 March 2007. This individual was then sighted in the Netherlands at Vooroever 1, 1671 SG Medemblik (N 52° 46´ 15” E 05° 07´00”) on 12 and 18 August 2023 – 16 years, 5 months and 2 days later and 8,429 kilometres (straight-line distance) from Swakopmund Salt Works! The sighting was reported to the Arnhem Scheme in the Netherlands, which reported it to SAFRING in Cape Town, South Africa, which in turn informed me.
There have been other notable records involving ringed Common Terns. On 26 November 2001, I found a dead ringed Common Tern on the beach opposite the saltworks. The bird had been ringed nine days before by Mark Boorman, a Swakopmund resident. On another occasion, a Common Tern I had ringed on 1 January 2011 was found dead in Norway on 15 April 2017. The birds depart from Namibia in April every year and fly up the African coastline to Europe and Scandinavia where they breed. On their way north, two Common Terns ringed by me, one on 24 March 2007 and another on 28 December 2011, were recaptured and released by a French bird ringer on 3 and 7 April 2013 respectively at Lagune de la Somone, 47 km southeast of Dakar in Senegal. The birds were on their way to their breeding grounds in Europe and Scandinavia.
In September every year, these terns travel from the Northern Hemisphere down south to spend the summer in southern Africa. They travel far more than the 8,500 km straight line between the points of capture and recapture because they follow the coastline and search for food along the way. This means that they travel around 20,000 km each year between the Southern and Northern Hemisphere.
Terns like to rest in shallow waters with small elevations where they can rest and are safe.
This Common Tern is in near-complete breeding plumage with a black-tipped red bill and black forehead, crown and nape.
Common Terns in non-breeding plumage in flight.
It was most probably the first time this immature Common Tern spent its wintering season between September and April in Namibia.
One Common Tern found dead at Langstrand between Swakopmund and Walvis Bay many years ago had been ringed as a two-year-old bird on an island off the coast of Germany. The bird was 26 years old when it died and had travelled more than 520,000 km in its life! This is a tremendous effort by a bird 31 to 35 cm in length, weighing between 95 and 160 grams and with a wingspan of 72 to 82 cm.
I have captured a few Common Terns at the Swakopmund Salt Works that were ringed in Finland (6), Belgium (3) and Denmark (3) and one that was ringed in Sweden. Mark Boorman has recaptured many more and from more countries. We have added our own rings to these individuals o make sure that we are informed if these birds are recaptured or recovered elsewhere.
The Swakopmund Salt Works are an important roost for Common Terns and many more seabirds. Unfortunately ringing efforts at the saltworks have been abandoned because of light pollution from the Vineta and Mile 4 developments. The entire Namibian coastline is an important international feeding ground with numerous roosts for migratory seabirds. The Walvis Bay Lagoon, Sandwich Harbour and Orange River Mouth are Ramsar sites, which means they are wetlands of international importance. Namibia has five Ramsar sites, the other two being Etosha Pan and the Bwabwata-Okavango Ramsar site at Divundu. TN
- An adult Common Tern halfway in breeding plumage in as early as March. This bird is not blind but blinking. Fortunately, birds have evolved a structure for protecting their eyes. Like humans, they have upper and lower outer eyelids, but beneath the outer eyelids lies an extra eyelid, called the nictitating membrane. Nictitating, for all its alliterative syllables, simply means “blinking”. This extra eyelid is hinged at the inner side of the eye and sweeps horizontally across the cornea. The nictitating membrane is largely transparent, and it helps keep the eye moist and clean while guarding it from wind, dust and injuries.
- This Common Tern is in non-breeding plumage with dark legs and a black bill.
- A local ring (left) was attached to a Common Tern which first was ringed as a chick in Sweden and then recaptured at the Swakopmund Salt Works. Common Terns spend the northern winter in the Southern Hemisphere before migrating back in our winter to breed in Europe and Scandinavia.
- This Common Tern ringed in Denmark (top ring) received a local (SAFRING) ring to make sure we are informed if the bird is recaptured or recovered anywhere in the world. In this way the Danish and Southern African ringing centres have to be informed and need to inform the ringers and those reporting the rings.
- An adult Common Tern in non-breeding plumage north of Swakopmund at the saltworks, a popular roost for terns. The bird had been ringed and measured a few minutes earlier and took some time to compose itself before flying off into the darkness. The red legs indicate that the bird is about to change into breeding plumage.
- The map shows the 8,429-km-long straight line between the point of ringing in Namibia and the point of resighting in the Netherlands.
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