Tropical Boubou - Taxonomy and Systematics

Taxonomy and Systematics

Traditionally, seven subspecies of the Tropical Boubou were recognized – that is, if L. aethiopicus was considered a distinct species at all. As late as the mid-20th century for example, some authors included the entire "Tropical Boubou" complex within L. ferrugineus, which nowadays refers to the Southern Boubou only.

Recent cladistic analysis of nDNA BRM15 intron-15 and mtDNA NADH dehydrogenase subunit 2 and ATP synthase F0 subunit 6 sequence data indicates that the "Tropical Boubou" as traditionally recognized is a polyphyletic cryptic species complex, and that three additional species should be recognized. Furthermore, as it seems the "Bulo Burti Boubou" – described as L liberatus from the only known individual trapped in 1988 – is actually a rare and hitherto unrecognized morph of L. (a.) erlangeri and should be considered its junior synonym.

Contrary to what one might expect in a purely phenetic analysis, the conspicuous variation of wing stripes is no good indicator of relationships among these and related boubous. Vocalizations and habitat preferences, on the other hand, allow a good delimitation of the clades conventionally grouped as "Tropical Boubou". The four proposed species are:

• Somali Boubou, L. erlangeri – S Somalia. Includes L. liberatus

Outer tail feathers never have white tips. Short wings stripe across the median coverts. Breast and belly pinkish. The liberatus morph has long white wing stripe like aethiopicus, and a yellowish-buff chin to chest and supercilium.

A quite ancient lineage, part of a rather basal group of mostly allopatric relict forms – the dark-bellied Mountain Sooty Boubou (L. poensis), Fuelleborn's Boubou (L. fuelleborni) and perhaps Slate-colored Boubou (L. funebris), and the sympatric light-bellied Red-naped Boubou (L. ruficeps) to which it might be closest. The western members of this group inhabit montane forest, the others dry shrubland. The liberatus morph may be an atavism of plesiomorphic alleles retained from a common ancestor with L. ruficeps, as the type specimen showed no indication of recent hybridization whatsoever.

Many taxonomists now consider it to be a distinct species

• East Coast Boubou or Dimorphic Boubou, L. sublacteus – Coastal Kenya, Zanzibar

Vestigial or no white wing stripe. Outer tail feathers may have white tips. Juveniles have no barring on underside. An all-black morph occurs in the area around the lower Jubba and Tana Rivers and on the Lamu Archipelago.

• Ethiopian Boubou, L. aethiopicus – E Sudan through Djibouti, Eritrea, Ethiopia and W Somalia to N Kenya

Breast and belly pinkish. Narrow wing stripe, extending across the median and larger wing coverts, and often a bit onto the secondary remiges. Outer tail feathers never have white tips.

• West African Boubou (Tropical Boubou in the strict sense), L. major – Sierra Leone east to Sudan, then south to the Great Lakes region, from there excluding the inner Congo basin southwest to the Scarp of Angola. Intergrades with mossambicus in the southeastern Congo Basin. Possibly hybridizes with Swamp Boubou (L. bicolor) in the Angola region.
  • L. m. ambiguus – Highlands of Kenya and NE Tanzania

In major, long narrow wing stripe across the median and larger wing coverts, and usually continuing onto the secondary remiges; breast and belly may be pinkish (particularly in northern birds) or off-white (as in most southern birds). In ambiguus, short wings stripe across the median coverts; breast and belly pinkish. Outer tail feathers may have white tips in both subspecies.

• L. "a." mossambicus – S Democratic Republic of the Congo, E Zambia, E Mozambique. Intergrades with major in the southeastern Congo Basin.

Smaller and buffier below than the northern populations. Long narrow wing stripe like in major. Outer tail feathers never have white tips.

• L. "a." limpopoensis – W Mozambique to S Zimbabwe and N South Africa. Hybridizes with Southern Boubou (L. ferrugineus) in Limpopo valley.

The buffiest of all, without pink tones. Long narrow wing stripe like in major. Outer tail feathers never have white tips.

These seem to be part of a close-knit and more apomorphic clade of parapatric to sympatric black-and-white (or -buff/-pinkish) boubous which mostly inhabit semihumid lowland habitat. Their relatives are Turati's Boubou (L. turatii) and perhaps Luehder's Bushshrike (L. luehderi), and the Southern and Swamp Boubous. L. sublacteus seems to form a distinct southern lineage with the last two, but the southernmost "Tropical Boubous" are too little studied. It seems certain that they belong to the second group, where they may be a southward extension of L. aethiopicus, but more likely represent the southwestern populations of L. major. The hybridization is liable to confound DNA sequence analyses, particularly of mtDNA.