Those Mystery Swifts: Horus, New to Senegal

(see also this Ornithondar post on the same topic, en Français!)

Back in January, when Frédéric Bacuez (Ornithondar), Filip Verroens and I visited the middle Senegal valley, we stayed the night at Gamadji Sare on the Doue river bank in the far north of the country. We had some really good birds here, such as Egyptian Plover, Red-throated Bee-eater, Fulvous Babbler, Cricket Warbler, and Seebohm’s and Isabelline Wheatears. We also encountered a flock of swifts which we initially took for White-rumped Swift as these had been reported from the Senegal valley before and since in Senegal this is the only swift with a white rump other than Little Swift.

However, something felt not quite right for this species, and luckily Frédéric was able to take a number of decent pictures – not an easy feat with these birds! Subsequent study of the pictures revealed that the birds did indeed not quite fit White-rumped Swift, and that they were something else… Frédéric was lucky to pay a second visit to the same site, in mid February, and despite very dusty conditions he obtained even better pictures. These provided a more definite clue to the identity of these mystery swifts, which we now feel confident are nothing less than HORUS SWIFTS!!!

Horus Swift / Martinet horus (© F. Bacuez) (1)

Horus Swift / Martinet horus (© F. Bacuez) (2)

 

Why do we get so excited about this one? It’s always exciting of course to find an addition to a country’s species list, but in this case we have a highly unexpected record since it comes down to a range extension of no less than 1,600 km, and because the species may even breed here. Plus, one can now safely assume that Horus Swift also occurs in Mauritania, Mali and Burkina Faso, and why not in northern Cote d’Ivoire and NE Guinea too (and for any WP listers out there: it may well make its way across the biogeographical border!). It also shows, once again, that there’s still so much to learn and to be discovered about birds in Senegal despite it being among the better explored countries in West Africa.

So far, the closest Horus Swift observations to Senegal were from Ghana, more precisely from Mole National Park and a few other locations in the NW of the country where they were first found in 2004, though it’s not clear whether these were incidental records of wanderers or whether the species is a resident here. It has also been recorded from SW Niger (‘W’ NP), several plateaux in Nigeria and the highlands in Cameroon, but only becomes relatively widespread in the highlands of East and Southern Africa.

Horus Swift range map from xeno-canto

 

On hindsight, the identification as Horus Swift is actually relatively straightforward, the key id features of Horus Swift being the following:

• Broad rectangular white rump patch extending well onto the sides of the lower flank (not narrow and U-shaped as in White-rumped)
• Moderately forked tail, intermediate in depth between Little and White-rumped Swifts
• Absence of white trailing edge to secondaries (a feature that’s almost always present in White-rumped)
• Overall structure and flight action closer to Little than White-rumped Swift, which is a slender bird with a graceful flight.

All of these are clearly visible on the pictures, some of which are shown below (merci Fred!). The option of a hybrid Little x White-rumped Swift was initially suggested, but all features fit Horus perfectly, and a hybrid would be slimmer with a smaller throat patch and some white edges to secondaries. Plus, it would be (near) impossible to have 18-20 hybrids together, without any pure birds. All swifts looked similar in the field, though pictures reveal that there may have been a Little Swift in the lot as well (picture here). A presumed hybrid was reported from Spain recently, see this eBird record. Our identification was confirmed by Gerald Driessens, illustrator of the reference guide to the swifts of the world.

Horus Swift / Martinet Horus (© F. Bacuez) (3)

Horus Swift / Martinet Horus (© F. Bacuez) (4)

 

The next three pictures are from February 12th, i.e. some five weeks later than our first observation when Frederic and Daniel Nussbaumer visited the site. Only a few birds were present, at least one of which showed a heavily worn plumage, see picture (6). Besides the shallow tail fork and large rump patch, the extensive white throat patch extending onto the upper breast is obvious here.

Horus Swift / Martinet Horus (© F. Bacuez) (5)

Horus Swift / Martinet Horus (© F. Bacuez) (6)

Horus Swift / Martinet Horus (© F. Bacuez) (7)

 

Here’s a more detailed description, largely based on the ca. 50 pictures by Frédéric :

Structure: typical swift build with a body shaped like a fat cigar and long and pointy wings, and a moderately forked tail, the fork being about a third of the length of the outer rectrices when closed.

• The wing shape resembled Little Swift much more than White-rumped, which has narrower wings. It often appeared to be fairly broad, particularly in the middle (inner primariers and outer secondaries). As can be seen on several of the images, the wing shape varied considerably throughout the birds’ flight action – for instance, compare pictures (3) and (4) which give very different impressions, and see also (8).
• The tail always appeared to be broad throughout, never pointed as is often the case in caffer (1) & (2). When completely fanned out, the fork appeared very shallow, quite similar to House Martin (2). At times it disappeared nearly entirely, thus resembling Little Swift: compare (6) and (7), of the same bird taken at an interval of a few seconds.

Plumage

• Overall very dark brown to black plumage except for the white throat, the very pale forehead extending to just above the eye (4), and the white rump;
• The rectangular white rump patch (4) clearly extended onto the flanks and was thus visible from below, e.g. pictures (5) and (6).
• The throat patch was similar to or larger than Little Swift, obviously extending onto the upper breast. Both features are nicely visible on (6) and to some extent on (1).
• Several photographs clearly show the relatively contrasting underwing pattern, stemming from a combination of paler brown leading edge-coverts, dark lesser underwing coverts, again paler median coverts, and slightly darker greater coverts – see header picture and (3) and (6). In White-rumped Swift, the lesser and median coverts are all darker than the remainder of the underwing.
• Upperwing entirely dark, without white trailing edge to secondaries. The latter appear slightly greyer or browner than the black mantle and scapulars (the “saddle”).

Voice: slightly lower-pitched trills than Little or White-rumped Swift; the short sound recording that I managed to obtain can be found here and contains two different calls, including a typical shrill swift call and a slower “twittering” of more melodious quality. It matches the recording by C. Chappuis quite well, both by ear and on sonogram, even if I find it hard to hear clear differences with some White-rumped Swift recordings (compare with e.g. this recording from Zambia). HBW describe the most common Horus call as a reedy trilled ”prrreeeeoo” or “prrreee-piu”. Of note is that until now, no recordings were available on xeno-canto or other online sound libraries.

Behaviour: the swifts were mostly feeding over the river and nearby banks, though usually remained above the water at various heights, occasionally flying right above the surface. They mostly remained in a loose flock, sometimes with 2-5 birds flying closely together and swooping close to the sand bank above which we were standing, sometimes calling in the process – a behaviour that’s indicative of breeding… The picture below shows two such birds “chasing” one another.

Horus Swift / Martinet Horus (© F. Bacuez) (8)

 

Below are a final few pictures from the January series:

Horus Swift / Martinet Horus (F. Bacuez)

Horus Swift / Martinet Horus (F. Bacuez)

Horus Swift / Martinet Horus (F. Bacuez)

 

Now compare with these pictures:

• Horus Swift

Horus Swift / Martinet horus (© C. Cohen, on ABC website)

Horus Swift / Martinet horus (© S. Helming, on IBC website)

• White-rumped Swift

White-rumped Swift / Martinet cafre (© S. Harvančík on IBC website)

White-rumped Swift / Martinet cafre (© H. Teichmann on IBC website)

 

The habitat in which we found these birds is also very much in line with what is to be expected from Horus Swift. Quite unlike most (all?) other swifts, the species breeds in “old burrows of bee-eaters, kingfishers and martins” (Borrow & Demey), i.e. typically in sandy banks along rivers – exactly the kind of place where we found these birds, which were seen “visiting” the Gamadji Sare cliff (approx. 6-8m at its tallest). Our swifts either rested on the cliff, or inside holes: at dawn on 6/1, several birds visibly left the river bank while the previous evening they were flying very close to or into the cliff, oftentimes calling (unfortunately, because we were positioned on top of the cliff, we could not confirm that they actually entered any nest holes). We estimated there to be about 18-20 birds on Jan. 6th, while the previous afternoon we saw just four.

It may thus even breed by the Doue river which likely has Pied Kingfisher and Blue-cheeked Bee-eaters, and possibly also Red-throated Bee-eater nesting here – something that we really ought to confirm in coming months (just before, during, or right after the rains?). White-rumped Swift typically breeds in disused swallow or Little Swift nests, though sometimes also “in crevices or on ledges within rock fissures or buildings” (Chantler & Driessens 1995). It may well breed at Popenguine for instance, where in September 2015 I saw two birds entering and leaving one of the World War II bunkers.

The Doue river by Gamadje Sare

 

As I was typing this up, I started wondering why a rather unassuming little bird such as this one was named after one of the most significant ancient Egyptian deities. Well, I’m not quite sure! It was described in 1869 by German zoologist Theodor von Heuglin, who spent many years in north-east Africa in the mid-19th century. One can assume that he collected the type specimen in Sudan or especially in Ethiopia where Horus Swift is locally fairly common. And that Heuglin somehow must have been inspired by Horus, depicted as a falcon-headed man, when coming up with a name for this species.

 

Many thanks to François Baillon, Simon Cavaillès, David Cuenca, Ron Demey, Gerald Driessens, Miguel Lecoq, Carlos Sánchez and others who commented on the identification or provided reference material.

 

Bram & Frédéric (une co-production Senegal Wildlife & Ornithondar!)

 

References

• Chantler, P. & Driessens, G. (1995) Swifts. A Guide to the Swifts and Treeswifts of the World. Pica Press.
• Chantler, P. & Boesman, P. (2018). Horus Swift (Apus horus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona.