September 24, 2016  

Where does Moltoni’s Warbler overwinter?

A recent observation of a Moltoni’s Warbler Sylvia subalpina near Gandiol (Saint-Louis) made me have a closer look at the occurrence of the species in Senegal and more generally in the species’ wintering areas.

This Sylvia warbler was recently recognised as a distinct species by several authors (Brambilla et al. 2008, Svensson 2013, and see also Shirihai 2001) and is now generally accepted as such by the various taxonomic authorities. Previously, it was regarded as a subspecies of Subalpine Warbler S. inornata (= new name for S. cantillans after the taxonomic reshuffle), but differences in plumage and especially vocalisations justify its elevation to species rank.

moltoniswarbler_mallorca_april2015-p-walser

Male Moltoni’s Warbler / Fauvette de Moltoni, Mallorca, April 2015 (P. Walser)

To summarize the current taxonomic status, which can be rather confusing owing to different scientific names being used in recent years, what used to be Subalpine Warbler S. cantillans is now widely considered as three separate species, following Svensson’s 2013 papers:

  • Western Subalpine Warbler S .inornata, with subspecies iberiae (Iberian Penninsula, S France) and inornata (Maghreb)
  • Moltoni’s Warbler S. subalpina (monotypic)
  • Eastern Subalpine Warbler S. albistriata with ssp. cantillans (S Italy) and albistriata (SE Europe)

“Subalpine Warbler” (in the old sense!) is a common non-breeding visitor in many parts of the Sahel, and is often the most abundant Palearctic passerine, including in northern and coastal Senegal and parts of Mali. At least here in Senegal, the majority are clearly Western Subalpines, but what about Moltoni’s? Its breeding grounds are quite well known: western Mediterranean islands (Sardinia, Corsica, Balearic Islands) and part of central and northern Italy, where locally sympatric with Western Subalpine. However, it quickly became clear that very little is known about the species’ distribution in winter and during migration in Africa.

Borrow & Demey show only a handful records on the distribution map in their field guide (2nd ed. 2014), in Nigeria, nothern Cameroon, and SE Mauritania. The Handbook of the Birds of the World and BirdLife, in typical fashion, haven’t adopted this fairly obvious split so far, though HBW does state that Moltoni’s Warbler is a non-breeding visitor to the “W Sahel”. Neither Morel & Morel nor Sauvage & Rodwell mention the species in their publications, though this is hardly surprising given that at the time Moltoni’s was “just” a little-known subspecies of Subalpine Warbler (that said, the Morels did recognise the inornata subspecies from NW Africa, which is likely a regular visitor to Senegal). Unfortunately, Ottosson et al. (2001) do not make any mention of subspecies involved even though they captured no less than 3,394 Subalpine Warblers in the Djoudj between 1987-1996 (out of 5,607 Sylvia warblers).

The only published records that I found of Moltoni’s Warbler for Sub-Saharan Africa all come from the African Bird Club‘s “Recent Reports”:

  • The earliest and so far most detailed reference comes from Nigeria: “among the Subalpine Warblers Sylvia cantillans mist-netted in Dagona Bird Sanctuary, northern Nigeria, in February 2007, the great majority proved to be of the subspecies moltoni […], with the rest being of the nominate race. Whereas the latter were very fat and not in moult, the former lacked any fat and were moulting their wing feathers. Adult S. c. cantillans and S. c. albistriata undergo a complete moult in their breeding quarters and the juveniles a partial one, whereas the moult of moltoni is very complex, with adults undergoing a complete moult either in their breeding or winter quarters, and the juveniles a complete moult in Africa. Previously, nothing was known concerning the wintering range of moltoni“.
  • In Benin, the first record was obtained just recently “in the far north-east at Kandi, Kargui and Karimama (Bello Tounga) on 18–21 November 2015, with singing individuals producing the characteristic rattle call.”

For Mauritania, I received this information from V. Salevski, who participated in several ringing campaigns run by the Swiss Ornithological Institute in the early 2000s both in Mauritania and Senegal: “I do not recall that I ever identified Moltoni’s Warbler in the field, but I recall that at least one was mistnetted in Tichitt, Mauritania, in autumn 2003. I myself assigned the respective bird(s) to Moltoni’s Warbler due to its moult pattern.” The location seems to corresponds with the record shown in Birds of Western Africa.

There are no known records from The Gambia, nor from Guinea-Bissau, nothing from Mali either and I didn’t find any info on Burkina Faso, Niger or Chad (comm. pers. C. Barlow, M. Lecoq, M. Crickmore, J. Brouwer). The West African Bird Database (WABDaB) does contain a handful of “Subalpine/Moltoni’s Warbler” records from Chad mainly, but none of these are sufficiently documented to ascertain the presence of Moltoni’s there.

Now what about Senegal? So far, I managed to uncover only 4 records, all from the north:

  • 1 near Richard-Toll early December 2013 (Birdquest; source: tour report by C. Kehoe)
  • two records of what were maybe two different males, 22 March 2014, Djoudj NP (J.-F. Blanc)
  • 1 male south of Djoudj, 7 April 2015 (J.-F. Blanc)
  • at least one near Gandiol, 11 September 2016 (pers. obs.)

Getting back to the original question of where Moltoni’s spends the winter: we still don’t really know, but it’s likely that its non-breeding range largely overlaps with Western Subalpine throughout the Western Sahel. It’s quite possible that the species is a regular migrant to Senegal even if the country may be just on the edge of its winter range, as one can imagine that there are greater densities further east, in Mali, Burkina Faso, Niger, northern Nigeria and Cameroon, and (western?) Chad. It’s quite possible that Moltoni’s also creeps into Ghana, Togo and Benin – as mentioned earlier, at least in the latter country it was recently confirmed to occur, but it’s not clear yet how regular the species is there. Unfortunately much of this region is off-limits to birders and researchers due to the prevailing security situation, so it will likely take some time before we find out more from this part of the Sahel. It’s clear though that at least in Senegambia the species is largely outnumbered by Western Subalpine Warbler, whereas this would seem to be the opposite in Nigeria.

The scant records listed here suggest that in Senegal it occurs throughout the non-breeding season, at least from early September to mid-April, and that it is not just a migrant transiting through in autumn and winter.  Further north, in Morocco (which unlike West Africa is fairly well covered by skilled observers), the taxon is considered an accidental visitor by the Moroccan Rare Birds Committee, and so far has been detected during spring migration only. The first record dates back to March 2008 from Merzouga while the second bird was trapped on 18 March 2013; there’s at least one additional observation, also from March (in Larache, 2016). These records suggest that some of the Moltoni’s – likely part of those that spend the winter in Senegal and probably southern Mauritania – migrate along the coast, while those that winter further east cross the Sahara through Algeria and Tunisia where they are “common” during migration (Svensson 2013), and possibly western Libya.

The species is said to arrive approx. 3 weeks later than Western Subalpine on its Mediterranean breeding grounds (Barriocanal & Robson 2011), but I didn’t find any info on differences in autumn departure dates. Moult strategy certainly seems to be different, but more research is needed. The Nigeria record seems to confirm that Moltoni’s depart later from West Africa than Western Subalpine, which in February had already completely moulted and were “very fat” as opposed to the Moltoni’s on the same site.

Ron Demey commented that if up to now there are so few definite records then this has everything to do with the fact that the taxon was just recently split from S. cantillans. Probably few birders are aware of the criteria, and it wouldn’t be surprising if Moltoni’s were widespread in the Sahel.

Ron is certainly quite right… but the question remains as to how widespread, and how abundant Moltoni’s Warbler is in its winter quarters. Does the range overlap completely with Western Subalpine, or may they have specific requirements in terms of habitat?  Are migration routes, timing and strategies different from Western Subalpine? I hope that more existing records will surface, and that birders visiting the region will pay more attention to the various Fauvettes passerinnettes in future, further helping to gain a better understanding of this little-known bird in West Africa. Pretty much the same applies to a number of other species pairs or recently split taxa, e.g. Atlas / Pied Flycatcher, Common / Iberian Chiffchaff, Western / Eastern Olivaceous Warbler to name but the most relevant that spring to mind.

And actually I don’t mind really – still lots to learn and lots of exciting discoveries in prospect!

moltoniswarbler_helgoland_oct2009-j-bisschop

A vagrant Moltoni’s Warbler in autumn, Helgoland, Oct. 2009 (J. Bisschop)

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Some references on Moltoni’s Warbler…

Of note is that Moltoni’s Warbler was initially designated as Sylvia moltonii by Italian ornithologist Orlando back in 1937, only later emerging that Sylvia subalpina took precedence (Baccetti et al 2007). Professor Dr. Edgardo Moltoni (1896-1980) was an eminent Italian ornithologist and director of the Museo Civico di Storia Naturale di Milano (Natural History Museum, Milan). Among other feats, he described Zavattariornis stresemanni (Moltoni 1938), the unique Stresemann’s Bushcrow endemic to southern Ethiopia.

Finally, thanks to all correspondents who provided information for this note, and to Jan and Paul for providing pictures!

 

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