Basically, there are two options. Two warblers that migrate to E Africa, of this size, with prominent pale wing panels, that wag their tails about and have pinkish-orange lower mandibles: the migratory elaeica race of Eastern Olivaceous Warbler (EOW) and Upcher’s Warbler (UW). Distinguishing between these two can be a real challenge – particularly if they are in rather worn plumage like the Tankatara bird. If you don’t believe me, just check out the millions of contracting comments on Facebook regarding this bird! Perhaps it is wise to first look at the age of the mystery bird. At this time of year, juveniles that hatched around June would be in fresh plumage, while adults would be quite worn after the breeding season. The Tankatara bird is fairly worn, although it still shows much of the pale edging to the feathers that will eventually get worn off almost completely. This suggests it is an adult bird, or second calendar year at the youngest. And what is it doing down here at the southern tip of Africa in August, when it should be fattening up for migration somewhere in Asia? Good question. The best theory I can muster is that this bird is a so-called reverse migrant, that somehow found its way south instead of north when it was supposed to return to its Asian breeding grounds in about March. It then spent the (southern) winter here, and was only discovered now (perhaps because it became more conspicuous at the changing of the seasons?). Who knows.
So can we identify it? Fortunately there are literally thousands of photos of the bird floating around on the Internet, in addition to many video clips and some sound recordings. There have also been lively and highly educational discussions by experts from all over the world (plus some quite dramatic politics, which I won’t get into in too much detail here). I personally spent an hour or two with this bird in the field as well. One of my ideas with this post is to summarize and collate the many disparate, ephemeral and transient comments that have been posted on Facebook and other channels. And objectively try to identify the bird based on the literature and expert input. But don’t take my word for it – this is just my personal opinion, and it is not in my capacity of a member of the SA Rarities Committee or any other official body. Make up your own mind based on the evidence.
I think the Tankatara bird is an Upcher’s Warbler. Here’s how I got to that conclusion:
Behaviour: To me, the movements of the Tankatara bird generally appeared slow, purposeful and ponderous, and its flight slow, heavy and low. It spent the majority of its time either low down in scrub or working along the outer edges and tops of bushes. It also spent a lot of time on the ground or hopping about on rock piles. It was remarkably unconcerned at the presence of hordes of birders, and foraged right out in the open for extended periods. Based on my very limited experience with EOW, and the literature, this sort of exhibitionist behaviour is more typical of UW and EOW. To me, EOW is a rather small, fast-moving, frantic thing, which generally sticks to the upper levels or canopy of tall bushes or small trees. It may descend to lower levels or even briefly alight on the ground, but for the most part is stays hidden in thicker vegetation. The tail movements of the Tankatara bird were also, in my opinion, generally slow and showy, unlike the constant nervous downwards tick of EOW but in line with UW. That being said, tail movement should only be seen as a supporting character. It depends on the bird in question, and the context. Tail wagging is said to be more subdued away from the breeding grounds. . Video clips illustrate behaviour best. Check out these, to start with:
Size: This is obviously difficult to judge in the field, but the Tankatara bird appeared rather big and heavy to me – I would say definitely bigger than a Reed or Marsh Warbler, though not by much. EOW is a smallish (slightly smaller than a Reed Warbler), lightly built bird, with a wing length of around 66 mm, and a mass of 7-16 g (lean weight 8.5-10.5 g). UW is a considerably bigger bird, with a wing length of around 76 mm; it is also a little heavier on average with mass 9.5-17g (lean mass 10.5-13.5 g).
Shape: The Tankatara bird is a closer fit to UW than EOW in my opinion. Compared to EOW, it has a heavier, fuller and broader-looking tail, a steeper crown (without the thin, long-nosed look of EOW), a short, thick neck, stronger legs and a more bulky body. However, at times it did transform into a sleek, skinny creature such as when stretching for insects.
Colouration: To be honest, I am not sure what to make of this. Having no experience with UW, it is difficult to evaluate the subtleties of grey and brown colour shades, particularly as the apparent colour changes dramatically depending on feather wear, light and angle. I would have expected a UW to be paler and more pure grey, whereas the Tankatara bird showed a warmer, more olive-tinged tone that would perhaps fit better with EOW. That being said, a search through hundreds of photos online suggests that colour is extremely variable and there is much overlap between the two species.
Wing panel: EOW may show a fairly prominent pale buff-tinged wing panel formed by the edges of the secondaries and lower tertials, but I would think that the very striking, full, whitish (not buff) panel on the Tankatara bird points more towards UW than EOW. Furthermore, EOW often shows particularly prominent white tips to the secondaries, which form a vertical white line on the folded wing; this is not the case in the Tankatara bird.