Terns are tough. I realized this anew this week while I was working through a mixed flock of mostly non-breeding terns at a roost on South Africa’s West Coast. The wind was picking up, and my eyes were watering from the sunblock my wife had insisted I apply. The rocks were digging into my back as I lay down awkardly alongside my scope, alternately sketching and spying. When I had arrived a few hours ago, I had gone through the typical mixed tern roost sequence. Right off the bat, everything looked different, and I got too excited too quickly, my mind racing with remote possibilities. Things took a tern for the worst when I started imagining that I had found a major local rarity.
Then, as I started working through the terns in more detail, they all morphed into same species! It was only after a few hours of scrutiny that I started picking up reliable patterns and consistent differences. It is important to take your time when working on tricky bird IDs – no book or app or guide can beat personal field experience. It also became clear that our standard field guides are nowhere near thorough enough when dealing with these troublesome birds. One can’t really blame them: there is a great deal of information to fit into one paragraph and depict in 2 or 3 illustrations/photos. Aaaaanywaaays, as Ellen would say, I thought I would share some of my observations here – to help you not only identify, but also enjoy and understand these remarkable seabirds.
“The flight of the spritely Tinker Bell in Disney’s animated feature is like the flight of the terns…these feathered, almost ephemeral pixies swirl on the wind currents with delicacy and sureness.” – Chris Petrak, tailsofbirding.blogspot.co.za
The problem: Roseantcommic Tern and the Boreal Bias
In a groundbreaking identification paper published in British Birds in 1993, Hume stated that “…identification of Common, Arctic and Roseate Terns in the field still presents a challenge. Many people stick too easily to ‘commic tern’ in their notebooks. It is a pity that the names lend themselves so well to such shorthand, but even those who try harder often struggle. Quite rightly, too, on occasion, as the terns are difficult and sometimes impossible; but given a good enough view they should not be.” Ah yes, the good ol’ Commic Tern – an amalgamation of the words Common and Arctic, and a conveniently noncommital moniker if you’re unsure about which species the bird belongs to. However, this term arose in the Palearctic, where these terns breed, and are typically seen in breeding plumage. So if the Brits, Dutch and Scandinavians struggle to differentiate terns in breeding plumage, what chance does our little Southern African birding community have? Remember, we see these terns mostly in non-breeding plumage, when bright colours and tail streamers are absent, and the birds are fairly quiet, and often far out at sea.
Another major problem for us down here in Safrica, is that all the specialist literature devoted to the identification of problem terns, often in painstaking detail, is written for readers in the Northern Hemisphere – thus the Boreal Bias. So the illustrations you see in your Collins or Sibley are not necessarily what you would see in Africa. This can be particularly problematic when it comes to characters such as the colour of the primaries, which change very rapidly from pale silvery grey (fresh) to blackish (worn). This can void identification characters mentioned in European books, such as the dark wedge on the middle of a Common Tern’s wing, which is a wear-related effect.
Another at best irritating, and at worst utterfly confusing effect of the Boreal Bias, is that the seasonal terminology used in ID articles and overseas field guides is the opposite to what we would use. They talk about “first-winter” in our summer. Their birds “winter” here, but we see them around Christmas in the middle of summer. Their spring is our autumn. Their fall is our spring. This can cause major cons-tern-ation. And just to muddy the waters a little further, we also have one species that breeds here in our winter (and is thus on the same cycle as the non-breeding Palearctic migrants). Plus, we have one species that is a non-breeding winter visitor. Is your head spinning (terning?). Mine certainly is. Hopefully this article, written from a decidedly Southern Hemisphere perspective, will help tern the tables.
In addition to Commic Tern, I think we should be wary of Roseate Tern too. Telling these from Commic Terns in non-breeding plumage can be devilishly tricky. And the identification of Antarctic Tern, which does not wander to the Northern Hemisphere and into European ornithological literature, has been much neglected. Indeed, identification texts dealing with Antarctics are often vague or contradictory. I hope this write-up will help a little, but it is by no means the final word. Perhaps I’ve got something completely wrong, or perhaps I’ve overlooked a useful feature. If so, I’d love to hear from you! So Roseantcommic Tern? You guessed it, Roseate + Antarctic + Common + Arctic.
But first, let’s meet the contenders…
Common Terns are indeed common, occurring along our entire coastline in summer, with a few immature birds present year-round. Maximum populations may reach 300,000-400,000 in summer, making this our most common coastal tern. The species breeds widely in North America and the Palearctic in the Northern Hemisphere summer (our winter). Ring recoveries have shown that most of our birds probably breed around the Baltic Sea, and especially Finland and Sweden. However, ringed birds have also shown connections between Southern Africa and Norway, Germany, the Nerherlands, Wales, Scotlat, France and Israel. Common Terns from Western Europe migrate down along the west coast of Africa, and those from further east along the East Coast. The species is exceptionally rare inland on migration. By the way, the Common Tern’s scientific name, Sterna hirundo, is also reflected in the historical name “Sea Swallow” for terns.
ABOVE: A Common Tern in breeding plumage photographed in July in Sweden. Most Common Terns develop only a faint greyish flush below (some are darker though). So there isn’t much contrast with the white cheek. They usually have red bills with black tips (all-black in Asian longipennis). The tail streamers are shorter than or level with the wing-tip. Photo by Stefan Berndtsson (link here).
ABOVE: A Common Tern photographed in June. I would guess this might be an overwintering first-year. If it was an adult, you would firstly expect to see some breeding plumage (full black cap and a slight grey wash below, with longer tail streamers, and red-based bill); and secondly, you would expect to see it in the Northern Hemisphere, not at Jakobsbaai on the West Coast. Photo by me.
ABOVE: A bunch of Common Terns resting. Note their conspicuous black carpal (shoulder) bars and solid black (not speckled) crowns. Photo by Phil Penlington.
Arctic Terns are famed for their incredible migration. Thanks to those pesky Pick & Pay wildlife cards, even toddlers know this. But let’s drop some Wikipedia stats anyways. With the advent of satellite tracking, we now finally have a clear picture of just how insane these little globetrotters truly are. Arctic Terns breeding along the frigid shorelines of Greenland or Iceland migrate around 71,000 km per year. The temptation to multiply this with the average lifespan is too great to resist: 30 years x yearly average = 2.4 million kilometres. Three times to the Moon and back, as the tern flies. Birds from The Netherlands fly even further: down the coast of Europe and Africa, then sho’t left just past Cape Town, and east to Australia or even New Zealand, then south to the Antarctic. One bird holds the record of the longest known migration for any animal: 91,000 km in a year. This species sees more daylight than any other creature, and has pretty much perpetual summer – making its scientific name of S. paradisaea quite fitting. Sick or exhausted Arctic Terns rarely join tern roosts along the coast, but for the most part they are pelagic, and migrate well offshore. They are most commonly encountered in spring and autumn on passage. But expect the unexpected: in September 1996, Dave Allan and Andrew Jenkins found an Arctic Tern flying above Katse Dam in Lesotho, not only 500 km from the sea, but also way up in the mountains!
ABOVE: An Arctic Tern in full breeding plumage is a handsome bastard. They are darker grey below than Common Terns, but not as dark as Antarctics (which can almost recall Whiskered Tern). Most breeding Common Terns would have a dark bill-tip (all-red in Arctic). Note also the very short legs, but long tail streamers extending beyond the wings. It is a small and petite bird, with a short neck, rounded head and short spike of a bill. Photo pirated off MaxPixel (link here).
ABOVE: These are more typical views that we can expect in South Africa, where Arctic Terns are highly pelagic and are very seldom seen ashore. I photographed this bird on the recent BirdLife South Africa Flock at Sea trip, somewhere SE of Cape Town. Even at this distance, you can make out some of the Arctic/Antarctic type features: very long white tail streamers and a pale upper- and underwing. This could also be an Antarctic on the way to South Africa’s shore, or out on a deep sea foraging mission. Photo by Faansie Peacock.
ABOVE: I am unsure whether these are Arctic Terns or Antarctics. Pretty bad pictures but I would have guessed Arctic based on the wing shape, dainty look, short-looking bill and narrow swept-back primaries. I would expect Antarctic to have darker, more worn primries by this time (March)…but the distinction between these two species at such a distance is a stretch. Let me know if you have thoughts.
ABOVE: Circling the entire planet was obviously not for this guy. This is an Arctic Tern specimen that I skinned at the Ditsong National Museum of Natural History. Check out those long tail streamers. The entire tail is white except for a black web on the outer vane of each outer feather (the tail is crossed here). Photo by Faansie Peacock.
ABOVE: I would say these primaries are still fairly fresh. The dark mottling on the carpal area and primary coverts may suggest this is a first-year bird. Common Terns would have darker primaries, and a dark grey bar on the secondaries, not the rather plain grey wing of this bird with a wide white trailing edge. Of course, also note the pure white rump (grey-washed in Common, but also white in Antarctic). Photo by Faansie Peacock.
ABOVE: Arctic Tern underwing. Note the short arm but long, narrow hand. The underwing is very pale overall – in fact, if you put it in front of a light, all of the inner primaries and secondaries are translucent (only the inner ones on Common, forming a triangular patch in middle of wing). Wonder what happened to that blue jersey of mine? Photo by Faansie Peacock.
We do have one breeding species, namely the Roseate Tern. This globally widespread bird is now classified as regionally Endangered, as the South African population size is estimated at less than 250 mature individuals. Worldwide, Roseates breed in North America, Azores, western Europe, from the Arabian Peninsula south to East Africa, on several Indian Ocean islands (including Madagascar), and eastwards to India, the East Indies and into the western Pacific and Australia. So in summary, much of planet Earth. Locally though, they breed only on three little islands off South Africa’s southern coast: Dyer Island (3-20 pairs); and in Algoa Bay off Port Elizabeth, St Croix Island (0-44 pairs) and Bird Island (70-300, average about 165 pairs). The latter island is also of critical conservation importance for its large Cape Gannet colony. By the way, this species is named S. dougallii, after Scottish doctor and amateur naturalist Peter McDougall (1777-1814); he received this honour because he shot some of these terns and sent them to George Montagu (he of the harrier), who described them as a new species in 1813.
ABOVE: So halfway through writing this article, I discovered that my friend Phil had copied a whole load of Roseate photos onto my hard drive many years ago. He might cringe at the quaity of these pics today, but I still think they are pretty spectacular and definitely illustrate this species very well! Thanks Phil. First off, the most important thing with Roseates is that rudely long and clearly drooped bill. This is a breeding bird which has started developing the red bill base, and has a full black cap. They are supposed to have a pink flush to the underparts – I always struggle to see this, but perhaps if you squint…Note also the orange (instead of dark red) legs. Photo by Phil Penlington.
ABOVE: This Roseate Tern is barely showing any red on the bill, but still has a full black cap and orangey legs. This posture nicely shows the very long tail streamers plus the exceptionally long, decurved bill. The plumage is retina-burning white in Roseates; notably more so than in other terns. Better underexpose a few stops. Photo by Phil Penlington.
ABOVE: A great many Roseates sport these green leg flags! This was photographed in the breeding season, so I suspect it’s a youngish bird. It also has a faint dark carpal bar (nowhere near as prominent as in Common Tern). The primaries of Roseates have very strong white inner webs, that form a distinctive pattern. This bird has a full black bill; non-breeding adults do too (as in Common and Arctic, and some Antarctics). Photo by Phil Penlington.
ABOVE: I suspect that this giraffe-neck posture forms part of the elaborate courtship and pair-bonding display of Roseate Terns. Unless I’m misinterpreting it and this is a form of aggression between rivals? The lower two are probably adults, with a first-year arriving. Note how white the wings look in flight. Photo by Phil Penlington.
ABOVE: The outer tail streamers of Rosies are disproportionately long, and they often flap around when the bird is flying. Photo by Phil Penlington.
Okay, are you still keeping track? We have one localized breeding species (Roseate); one common non-breeding summer visitor (Common); and one rare passage migrant (Arctic). And now the pièce de résis-terns. We also have a non-breeding winter visitor, one of the very few winter immigrants to our region. The Antarctic Tern, Sterna vittata, and the focus of this article. So as their name implies, these terns are the polar opposites of Arctic Terns. They breed on the Antarctic Peninsula, as well as various sub-Antarctic and Southern Ocean islands, in the southern summer. This includes South Africa’s Prince Edward islands; therefore the conservation of that breeding population is our responsibility. After breeding, some of these birds migrate to the coasts of Argentina and South Africa, where they join mixed tern roosts on coastal rock outcrops, offshore islands, small bays or sheltered beaches. The world population is probably in the order of 45,000 pairs and around 10,000 visit South Africa from May to October. The biggest roosts are on islands (e.g. Bird Island, Dyer Island, Dassen Island) with mainland roosts typically hosting fewer than 900 birds (often just a few). The name vittata means a longitudinal stripe, in reference to the white cheek stripe that separates the black cap and grey throat.
ABOVE: This is the map I made for the 2015 Eskom Red Data Book of Birds of South Africa, Lesotho and Swaziland (see details here). It shows part of the breeding range of Antarctic Tern and the various subspecies on the different sub-Antarctic islands.
ABOVE: An Antarctic Tern just starting its post-br. moult out of br. plumage as evident by the one or two white feathers on its forehead. It is essentially the Southern Hemisphere version of Arctic Tern, although a little bigger and a lot less migratory. Note the entirely red bill, reg legs and grey wash below, contrasting with the white cheek stripe. Early June, Jakobsbaai. Photo by Faansie Peacock.
ABOVE: An intensely coloured Antarctic Tern (probably a male of the race vittata). This is still pretty much full br. plumage, with the prominent white line on the cheek contrasting with the black crown and grey throat. Unless you see the deeply forked tail, you could momentarily mistake this for a Whiskered Tern. Early June, Jakobsbaai. Photo by Faansie Peacock.
ABOVE: I would say this Antarctic Tern, photographed in early June on the West Coast, is about halfway between breeding and non-breeding plumage. You can see from how black the outer primaries are that these are very worn and will soon be replaced. Photo by Faansie Peacock.
ABOVE: When I initially saw this Antarctic Tern with its exceptionally long tail streamers, I though Roseate. But of course the bill is not nearly long and droopy enough, and would never be all-red in Roseate. That species would also be much whiter, with paler primaries and orangey feet. The feet of this bird have turned dull maroon, but its beak is still solid and bright red even though it is in non-br. plumage. Photo by Faansie Peacock.
ABOVE: On the other hand, many Antarctics at the same time had entirely black bills, or just showed a tiny tinge of red at the base. This bird also has darker legs and fresh primaries. It might be a failed breeder that started moulting early on, or something like a second winter. Note the large, rounded, domed head – very different from Common – and the dumpy shape. Photo by Faansie Peacock.
ABOVE: Antarctic Terns can have really impressive tail streamers that extend well beyond the folded wing at rest. Photo by Faansie Peacock.
Perhaps it would be prudent to just mention some other possibilities, and a handful of vagrants. You never know right?
|A common breeding species and partial migrant.
||Inland wetlands in much of SA.
||Quite like a br. Antarctic with white cheek stripe, but darker and almost black on belly (contrasting strongly with white vent); bill and legs maroon. Tail shallowly notched (not deeply forked). Marsh terns (Chlidonias) incl. Whiskered, White-winged and Black, have lazy, banking flight and tend to pick prey from the water surface (do not hover and dive like sea terns).
|Very rare vagrant. 3 records in N Coast of KZN.
||From Kenya to Arabia and India.
||Similar to br. Antarctic, but most likely in summer, and entire rump and tail grey. Not easily told from other terns in non-br. plumage.
|Unlikely potential vagrant.
||Breeds N America; winters C America.
||Like Common Tern but wing very plain (almost all-white above). Rump white. Tail extends beyond wings. Non-br. has an (almost) isolated black face mask, like a Gull-billed Tern, plus longish orange legs.
|South American Tern
|Very unlikely potential vagrant.
||Breeds along coasts of S America. S birds migrate to warmer latitudes.
||ID not clear, but highly unlikely to reach us. Heavier, bulkier bird with a stronger bill and longer legs. Often white crescent below eye in non-br.
|Highly unlikely potential vagrant, except if ship-assisted.
||One of the rarest terns. Only 3,500-6,500 in the world. On Crozet, Prince Edward and Kerguelen islands.
||Sedentary and thus highly unlikely to reach SA. Like Antarctic but smaller (like Arctic), with shorter tail streamers and grey-washed rump and tail.