A Common Yet Swift Antarctic Sandwich

The early morning dog-walking community that amble, stride and, at high tide, trudge through the shifting white sands of Long Beach in Kommetjie are a special group of people that delight in the fact that we have the good fortune of sharing this dynamic environment with a substantial assortment of coastal critters. Walking along this beach as the sun peaks over the distant mountains and begins its daily journey across our skies; one is likely to meet an assortment of fascinating people; armed with binoculars, cameras and a steely resolve; who are not only exercising their furry friends or debating philosophy but also marvelling at the abundance of life congregating on our shores. They are there to witness the flocking coastal birds and leaping whales, stalk the elusive Cape clawless otter (Aonyx capensis) and even, in a feat appearing somewhat peculiar to most, venture a swim in the frigid Atlantic waters crashing onto the sand. Perching on a secluded rock to quietly observe the surroundings will inevitably have the observer enthralled by some curious happening; be it an otter slinking out of the surf with a crayfish tightly grasped in its jaws, the stark contrast of a shocking pink flamingo flyby against a gunmetal grey sky or the bulky torpedo-shaped shadows of the Cape fur seals (Arctocephalus pusillus pusillus) swiftly darting between the kelp beds after shimmering shoals of sardines (Sardinops sagax).

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Flamingos feeding at the Kom in Kommetjie

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Cape clawless otter feeding on a West Coast rock lobster (Jasus lalandii)

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Cape fur seals sunning themselves in between chasing sardine between the kelp stands

While the blend of wildlife that occurs along these shores shifts with the seasons; the moody skies offset by spectacular sunsets, the raw power of the wild seas and the profusion of life assembling in this environment makes winter the most impressive season to witness. The floating blue community is transported on the swell driven by the north winds of winter, pods of acrobatic humpback whales (Megaptera novaeangliae) bypass our coast during winter and spring as they travel between the Antarctic and the tropical waters of Mozambique while southern right whales (Eubalaena australis) migrate from their icy feeding grounds in the Southern Ocean to calve in the warmer waters off the Cape. Flocks of terns can be seen sheltering in the bays, swooping and gliding on the air currents and dropping dramatically out of the sky like accurately shot arrows into the rough white-capped seas as they track the shoals of sardines. It is these birds; turning the sky white as they soar high above the dunes, the air thick with their harsh squawking calls, that brought about a request from one of the dog-walking regulars. Brian is fascinated by the many tern species, both resident and migratory, that call Long Beach their home and after several years of photographing these squat little winged creatures, is interested in finding out more about their migrations and life history patterns.

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Floating Blue Community, and an orange brittlestar

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Over the past three years, superpods of humpback whales have been observed feeding off South Africa’s West Coast

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Southern right whales use the relatively calm waters of False Bay to calve

Over the years I have encountered a number of tern species foraging off Kommetjie’s fertile shores, the most frequently observed being the common (Sterna hirundo), swift (Thalasseus bergii), Antarctic (Sterna vittata) and sandwich (Thalasseus sandvicensis), hence the strange yet intriguing title. A lone Caspian tern (Hydroprogne caspia) can also occasionally be spotted gliding elegantly above the surf, its black-tipped red bill a striking feature against its lightly coloured plumage. Of the four species common to the area, only the swift tern is a resident in South Africa throughout the year, both the common and sandwich terns being Palearctic migrants originating from breeding grounds in Scandinavia and the Baltic Sea and Western Europe respectively. The Antarctic species, of which there are three well-defined subspecies, breeds on the sub-Antarctic Islands, including Tristan, Gough and Prince Edward, as well as the Antarctic Peninsula during the summer months while being a fairly common winter migrant to coastal South African waters. The diet of all four species includes small fish, the swift tern being a prominent participant in the annual Sardine Run phenomenon off Port St Johns on the Eastern Cape coast of South Africa.

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Caspian tern fishing off Long Beach with Table Mountain and Chapman’s Peak in the background

Swift terns are widespread along the coasts of the Indian, Atlantic and west-central Pacific oceans; breeding in Australia, Namibia and the west coast of South Africa (including important breeding colonies present on Robben, Dassen, Jutten and Schaapen islands). The South African population of this species fluctuates substantially as a result of the variable distribution of the combined biomass of sardine (Sardinops sagax) and anchovy (Engraulis capensis), breeding only in years when food is abundant (Crawford 2003). Due to this heavy dependence on local prey stocks, this species is highly nomadic with the numbers frequenting the breeding localities mirroring the considerable fluctuations in the abundances and distributions of pelagic fish off South Africa (Crawford 2009). The dramatic shifts in numbers was highlighted by Cooper et al. in 1990. A complete breeding census was carried out in 1984 when the breeding population was estimated to be at 4 835 pairs across the 22 localities, greatly contrasting with the numbers recorded in 1988 when 6 088 pairs were counted in only three of the localities. The need for these birds to carry food for their chicks in their bills, supports the theory that they must breed in close proximity to their food supply and thus results in the low site fidelity observed in these birds (Crawford et al. 2002). These birds are monogamous with the pair bond maintained during the year, sometimes lasting from year to year. The majority of the swift tern population breeds in the Western Cape region of South Africa and is normally confined to the Jan-Jun period, peaking in Feb-Apr and occasionally extending to Aug/Sep (Sinclair & Ryan 2009).

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Swift terns hunker down and ride out the storm

The non-breeding distribution of the South African population extends from Swakopmund in Namibia to Kosi Bay in Kwa-Zulu Natal, with a few individuals being documented in Tanzania and Mozambique (Cooper et al. 1990). Their numbers were recorded as fluctuating between 1 449 and 5 668 pairs across 13 localities during the 1987-2000 study period (Crawford 2003). The continuous movement between these breeding localities may drive swift terns to seek out sites already occupied by other breeding seabirds as presumably these would be deemed a safe and suitable environment in which to nest. Swift terns are often associated with breeding Hartlaub’s gulls (Larus hartlaubii) and crowned cormorants (Phalacrocorax coronatus); seabird species with a dissimilar diet and therefore not competing with the terns for food (Crawford 2003). The South African population of swift terns is highly mobile with adults leaving the breeding sites at the end of the breeding season and moving east to the Indian Ocean coastline of the Eastern Cape and Kwa-Zulu Natal. The fledglings also trek east, often rapidly dispersing from the Namibian and Western Cape breeding colonies. A nestling banded at Robben Island, in Table Bay, was recovered 3 months later in Sodwana Bay, 1 716 km away, as the tern flies (Crawford & Dyer – Private Notes).

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Juvenile swift tern (Photo Credit: Brian Preen)

Terns are renowned for covering extensive distances over a relatively short period of time. The large majority of the sandwich terns originate from the colonies on the west European Atlantic seaboard and the Baltic Sea, with low numbers starting their journey in the Mediterranean and rare visitors from the Black and Caspian seas, and making an appearance on our shores (Underhill et al. 1999; Tree 2011). The sandwich tern differs from the swift tern in that they are more of an inshore feeder, preferring estuaries to the offshore islands, although do sometimes undertake nocturnal missions to join roosting assemblages of other tern species, especially swift terns (Tree 2005; Tree 2011). Just as in the case of the swift tern, the southern African distribution of the sandwich shows an emphasis shift from year to year as well as between the decades; a food-related driver being suggested as the cause (Tree 2011). While these migrants summer in southern Africa (early-birds arriving at the beginning of September and the stragglers leaving our coasts at the beginning of April) their movement is continuous, their visit beginning along the west coast and gradually shifting east during the course of their stay (Tree 2011). The extreme mobility of these birds throughout the season was documented in January 1986 by the recovery of a bird in KwaZulu-Natal just 18 days after being banded in the Eastern Cape, 849 km away. The migration north, often embarked on as night falls, is often taken at a leisurely pace with the birds averaging less than 100 km per day (Tree 2011).

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The winter of 2014 saw a mini-Sardine Run in the waters between Hout Bay and Kommetjie, resulting in high numbers of terns and seals making themselves at home on the surrounding beaches (Photo Credit: Brian Preen)

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Swift tern catches supper (Photo Credit: Brian Preen)

Ringed terns reveal the extraordinary feats of long-distance travel with Arctic terns (Sterna paradisaea), a maximum wingspan of approximately 85 cm, currently holding the world record. The time-frame in which these little feathered torpedoes complete these journeys is nothing short of astounding. Then again, their journeys are not limited by back-achingly-long layovers spent in some obscure airport, smelling of sweaty feet, contorted into a human pretzel in an unsuccessful attempt to get comfortable in the airport lounge or running to catch connecting flights that question the geographical knowledge of the airlines and the time-telling skills of the travel agents. Arctic terns, mainly from Western Europe, are a fairly common Palearctic migrant to coastal and oceanic waters. Most of these birds pass offshore while on route to and from their Antarctic wintering grounds with a small proportion remaining over summer (Sinclair & Ryan 2009). In 2015, geo-locators were fitted to twenty-nine terns at one of Farne Islands’ breeding colonies off the coast of Northumberland. Barrett (2016) documented that one of the locators revealed a mission of epic proportions. This jetsetter left its breeding colony, heading south along the west coasts of Europe and Africa and after rounding the Cape of Good Hope made its way into the Indian Ocean, arriving on the east coast of Antarctica twelve weeks after setting out. After completing this journey in reverse to return to its Northumberland breeding site, this bird had flown approximately 96 000 km; breaking the previous record by 5 000 km. It is estimated, given that terns are long-lived (34 years being the oldest recorded age for this species) that these birds are capable of travelling more than 3 000 000 km during their lifetime.

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Aggregation of Hartlaub’s gulls and terns on Noordhoek Beach (Photo Credit: Brian Preen)

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The sky is transformed into a white, squawking mass of hunting terns (Photo Credit: Brian Preen)

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Noordhoek Beach becomes a temporary time-out from fishing (Photo Credit: Brian Preen)

As it “terns” out, these long migrations not only allow these birds to rapidly rack up their “Frequent Flyer Miles”; they sometimes include stowaways, as evidenced during the mass mortality event of 1961 when a virus similar to the Influenza Virus A/Chicken/Scotland/1959 strain appeared in the migrant population of common terns summering on South Africa’s shores (Becker 1966). The common tern, as its name suggests, is the most common migrant tern to visit the Cape Province in the austral summer, October to February. 1961 however, experienced a shift from this annual movement behaviour when a substantial proportion of the migrant population delayed their departure from the Cape, to their breeding grounds in the temperate North, until May (Rowan 1962; Becker 1966). During April, many of these birds became ill and died. The first deaths were recorded in the south-western Cape during early-April with a sudden and virtually simultaneous third week peak in mortality at all localities between Lambert’s Bay in the west and Port Elizabeth in the east (Rowan 1962).

While the full extent of the event is still unknown, this host-specific epizootic was responsible for 1 300 deaths in four small roosting sites while  approximately 40 corpses were recorded at sea (offshore from Cape St. Francis and Bird Island) by Captain le Gras, fishing vessel skipper, and noted as an extremely rare event (Rowan 1962). The delayed departure, the sudden peak and abrupt cessation of mortality, as well as the six-month interval between the October arrival of the migrants and the April onset of the epizootic, puzzled researchers; resulting in various environmental parameters being examined. Local marine and meteorological conditions during March and April 1961 were scrutinised in an effort to explain this mass mortality event and while no definitive answers were uncovered, a combination of atypical conditions became the favoured theory. It has been observed that during years when abnormal oceanographic conditions prevail, illness and mortality become more pronounced (Murphy 1936; Rowan 1962). According to the “Monthly Weather Report – March 1961” from the South African Weather Bureau, five times the amount of rain normally recorded for the region fell over the Cape’s interior with “good” rain being experienced throughout April; this resulting in the flooding rivers transporting large amounts of silt into sea (Weather Bureau 1961; Rowan 1962). This coupled with the presence of an extensive red tide observed between Cape Town and False Bay at the time, was thought to be responsible for escalating the extensiveness of this event (Rowan 1962). An extensive study and conclusive evidence could not be produced due to the rapid onset being followed by the abrupt cessation of mortality and migration of the remaining birds.

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Swift terns, Hartlaub’s gulls and a white-breasted cormorant making the most of the mini-Sardine Run off Kommetjie (Photo Credit: Brian Preen)

On 18 October 2015, I had my own personal encounter with one of these long-distance feathered travellers when I recovered a ringed Arctic tern while walking my dog on Long Beach, Kommetjie. I was alerted to its presence by a frantic flapping in a tangled mound of recently washed-out kelp. On closer inspection, I discovered a severely distressed young tern with a piece of hard plastic, its bill having pierced it, obstructing its nostrils and preventing its bill from opening. After removing the plastic, I photographed the ring that I had noticed on its right leg and transported the exhausted bird to SANCCOB in Table View. I contacted the rehabilitation centre for daily updates on little “Thorvald” (sex was undetermined and “776621” didn’t have the right “ring” to it; plus I thought that he needed a strong name to get him through his recovery and looked like a “Thorvald”) but after spending the week in ICU, he sadly succumbed to his injuries and died on 25 October 2015. Armed with his ring number, I contacted the Iceland Museum of Natural History to find out more about the life and times of young “Thorvald”. He was ringed in East-Iceland on 13 November 2013 when he was still too young to fly freely. In the 827 days that this bird was ringed, he covered a distance of
11 321 km; only to be stopped by a piece of plastic, the spread-extent of which is choking the earth at a disgustingly rapid rate.

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Figure 1: Bird Recovery Report sent to me from the Iceland Museum of Natural History

While the Arctic tern is receiving accolades for its marathon-style Pole-to-Pole journeys, its Antarctic counterpart is a Southern Ocean local; found happily floating around on ice-floes or icebergs when not breeding on one of the sub-Antarctic islands. These birds feed at sea, often observed up to 150 km offshore, and their South African distribution ranges from Hondeklipbaai in the Northern Cape to Cape Pardone in the Eastern Cape with vagrants being recorded in Walvis Bay and Kwa-Zulu Natal (Tree et al. 2001). Antarctic terns are gregarious roosters and, like the swift tern, do so in the company of gull species. According to the University of Cape Town’s (UCT) Animal Demography Unit (ADU), the world population is estimated at approximately 45 000 pairs, 15 000 birds of which regularly visit South Arica’s coast. The largest roost being at Algoa Bay’s Bird Island where numbers exceed 5 000 individuals in August. As with the ringed Arctic terns, ringed Antarctics have revealed some interesting travel stories of their own. An immature individual ringed at Dyer Island, Western Cape, was recorded twenty years later on Gough Island in the South Atlantic Ocean while an adult that was ringed on Dassen Island was recaptured at its nest on Kerguelen Island in the South Indian Ocean. After a request was sent out in September 2000 to all researchers visiting Southern Ocean Islands to be on the look-out for newly ringed and leg-flagged birds, Eric Woehler (Australian Antarctic Division) observed a bird on Heard Island three months after it had been ringed at Bird Island; 4 300 km away.

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Swift tern soaring high above Long Beach (Photo Credit: Brian Preen)

So, the next time that you are wandering the wild shores of South Africa, keep an eye out for one of these charismatic travellers; you never know, you might be eyeballing the next Takahiro Sunada (no, Usain Bolt doesn’t work, these birds are not sprinters) of the feathered world.

Explore. Dream. Discover.

If you come across a distressed coastal bird in the greater Cape Town area please contact SANCCOB on 021 557 6155 or after hours on 078 638 3731. You can also contact the SANParks office at Boulders on 021 786 2329.

You can contribute your avian sightings to either the ADU Bird Sighting System or the SAEON/BirdLife Atlas of Seabirds @ Sea.

ACKNOWLEDGEMENTS

I would like to thank Brian Preen for the use of his beautiful photographs (credit on individual photos while uncredited photos are, as always, all my own). I hope that I have managed to answer your questions.

I would also like to extend my gratitude to Bruce Dyer and Rob Crawford for providing me with a couple of hard to find papers and answering some pretty inane questions.

REFERENCES

BARRETT RT. 2016. Upwind or Downwind: The Spring Arrival of Arctic Terns Sterna paradisaea at Troms, North Norway. Ringing & Migration 31(1): 23-29.

BECKER WB. 1966. The Isolation and Classification of Tern Virus: Influenza Virus A/Tern/South Africa/1961. Journal of Hygiene 64: 309-320.

BRANCH GM, GRIFFITHS CL, BRANCH ML & BECKLEY LE. 2010. Two Oceans: A Guide to the Marine Life of Southern Africa. Cape Town: Struik Nature.

COLLINS R. 2016. Arctic Tern Completes Longest Journey Every Recorded. [ONLINE] Available at: http://www.irishexaminer.com/lifestyle/outdoors/richard-collins/arctic-tern-completes-longest-journey-every-recorded-416985.html

COOK T. Date Unknown. The Swift Tern: A Paradox. [ONLINE] Available at: https://sites.google.com/site/timotheecook/a-paradox

COOPER J, CRAWFORD RJM, SUTER W & WILLIAMS AJ. 1990. Distribution, Population Size and Conservation of the Swift Tern Sterna bergii in Southern Africa. Ostrich 61: 56-65.

CRAWFORD RJM, COOPER J, DYER BM, UPFOLD L, VENTER AD, WHITTINGTON PA, WILLIAMS AJ & WOLFAARDT AC. 2002. Longevity, Inter-colony Movements and Breeding of Crested Terns in South Africa. Emu 102: 265-273.

CRAWFORD RJM. 2003. Influence of Food on Numbers Breeding, Colony Size and Fidelity to Localities of Swift Terns in South Africa’s Western Cape, 1987-2000. Waterbirds 26(1): 44-53.

CRAWFOR RJM. 2009. A Recent Increase of Swift Terns Thalasseus Bergii off South Africa – The Possible Influence of an Altered Abundance and Distribution of Prey. Progress in Oceanography 83 (1-4): 398-403.

CRAWFORD RJM, MAKHADO AB, WHITTINGTON PA, RANDALL RM, OOSTHUIZEN WH & WALLER LJ. 2015. A Changing Distribution of Seabirds in South Africa – The Possible Impact of Climate and its Consequences. Frontiers in Ecology and Evolution 3(10): 1-11.

ICELANDIC BIRD RINGING SCHEME, ICELAND MUSEUM OF NATURAL HISTORY, REYKJAVÍK, ICELAND. 2015. Ringed Bird Recovery Report – 19 October 2015.

MURPHY RC. 1936. Oceanic Birds of South America. New York: The Macmillan Company.

ROWAN MK. 1962. Mass Mortality among European Common Terns in South Africa in April-May 1961. British Birds 55: 103-14.

SINCLAIR I & RYAN P. 2009. Complete Photographic Field Guide: Birds of Southern Africa. Cape Town: Struik Nature.

TREE AJ, KLAGES N & UNDERHILL L. 2001. Antarctic Tern Sterna vittata. [ONLINE] Available at: http://adu.org.za/sp329_00.php

TREE AJ. 2005. Tern Status Report for the Eastern Cape, 2003/2004. Bee-eater 56(1): 6-11.

TREE AJ. 2011. Origins, Occurrence and Movements of Sandwich Tern Thalasseus sandvicensis in Southern Africa. Marine Ornithology 39: 173-181.

UNDERHILL LG, TREE AJ, OSHADLEUS HD & PARKER V. 1999. Review of Ring Recoveries of Waterbirds in Southern Africa. Cape Town: University of Cape Town, Avian Demography Unit. 100-102.

WEATHER BUREAU, DEPARTMENT OF TRANSPORT, SOUTH AFRICA. 1961. Monthly Weather Report – March 1961.

10 thoughts on “A Common Yet Swift Antarctic Sandwich

  1. Fascinating write-up, Sally, although it has to be said – not what I expected from the title 😀 I’ll certainly look at these birds differently now!!

    Liked by 1 person

    • Haha thanks Cathy 😊 I find that some science articles, and their titles, to be very wordy and, as such, put a lot of readers off. Science is a fascinating field, especially when focusing on natural systems and processes, that people should be excited about discovering. A catchy title or quirky fact can go a long way in sparking an interest in a certain topic…so, I try 😋 Thank you for the encouragement and I hope you enjoy your newfound feathery outlook 😊

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      • Yup – if I can’t get through the title, chances are I ain’t gonna get through the article! One of the things I really enjoy about your write-ups is the humour you weave into the fascinating facts – makes for enjoyable as well as educational reading!

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      • Thank you 😊 I am the same; at varsity I often viewed lit reviews as an onerous task instead of a journey of discovery and enlightenment, which is completely counterintuitive but understandable to a certain degree. I’m glad that you are enjoying my articles and am really looking forward to researching and writing my next one 😀

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  2. Fantastic read! Thank you for painting such a vibrant live portrait with words on animal life in Kommetjie. We are so blessed to live hear and be a part of it all. Stunning photos too. Love the one of the otter the most. A real gem!

    Like

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