African Broadbill Smithornis capensis Scientific name definitions

12–14 cm; male 21–26·9 g, female 17·4–27·5 g (South Africa), unsexed 20–31 g. A stocky, short-tailed bird with distinctive broad, flat bill. Male has buffish forehead, black crown, greyer ear-coverts, grey lower nape; upperparts and tail rufescent brown, sometimes tinged grey, mantle and back with broad black streaks; feathers of mantle and upper back with silky white feather bases (usually concealed); median wing-coverts with distinct buffy or cream tips forming wing-bar, greater coverts with narrower tips; flight-feathers mostly dark brown, outer 4 or 5 primaries twisted; underparts white, tinged buffish on breast sides and flanks, and heavily streaked blackish except on central belly and vent; iris dark brown; upper mandible black, lower whitish; legs and feet olive to yellowish-green. Differs from S. sharpei in smaller size, no orange on underparts; from S. rufolateralis in white or buff, rather than bright orange, breast side. Female resembles male, but duller, has crown grey with black streaks. Juvenile like female, but has less buff on forehead, brown crown with indistinct streaks. Races vary in colour and pattern above, extent of streaking below, female crown pattern, and size: camarunensis is darker, more rufescent, above than other races, breast more broadly streaked and with strong buff wash, female crown varies from almost plain black to heavily streaked black and rufous; <em>delacouri</em> resembles previous, but paler, with greyer nape and top of mantle; <em>albigularis</em> has white-streaked grey ear-coverts, greyer upperparts than nominate, yellowish-buff wash on breast, female crown blackish with buff edgings; <em>meinertzhageni</em> is like previous but underparts less buffy, female crown all blackish; medianus is not so dark as previous, also less streaked above and below, with grey wash over upper mantle, ochraceous breast patches, more yellow-buff belly, longer wings, female crown blackish-grey with faint pale scaling; suahelicus differs from last in dark grey ear-coverts, more extensive black on central mantle, female has more uniform crown, buff wash below; conjunctus has buff ear-coverts, yellowish to buff-olive wash on breast and flanks; <em>cryptoleucus</em> is more buffy-olive above than previous, female crown olivaceous slate-grey with broad dull black streaks.

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Editor's Note: Additional distribution information for this taxon can be found in the 'Subspecies' article above. In the future we will develop a range-wide distribution article.

Broader range of habitats than other African broadbills: lower storeys of evergreen forest , riparian forest, dense savanna woodland, areas of bamboo stands, dense deciduous thickets, miombo woodland, coastal bush; also disturbed areas with mosaic of forest and scrub, montane forest patches, including areas dominated by tree ferns; locally in plantations, cultivation, and open country around villages. Occasionally found in primary forest in E Africa ; very rarely so in W Africa, where it prefers drier areas outside the evergreen-forest belt. Also occurs in logged forest, also in pine (Pinus) plantations, particularly mature stands, and where clumps of other vegetation (e.g. bamboo) present. Differs from S. rufolateralis in preference for more open forest and forest edge. At up to 2550 m, but usually below 700 m; records at higher altitudes mostly from E Africa, where race medianus wholly montane.

Resident; it has recently been suggested that some local seasonal or altitudinal movements in NE South Africa could account for many records of this species in and near an area where it was previously unknown, although other data indicate that it is resident there.

Insects, including orthopterans, Coleoptera adults and larvae, hemipteran bugs, ants, caterpillars, butterfly eggs; also spiders. Sallies from perch in the manner of e.g. wattle-eyes (Platysteira), returning to same perch; also searches under leaves and branches, and occasionally on the ground. Sometimes joins mixed-species flocks passing through its territory.

The three members of the Smithornis genus share a peculiar display flight involving a mechanical sound made by the wings. African Broadbill is fairly widespread and common, yet its presence is usually only revealed by this far-carrying mechanical sound, which is quite unique among passerines. The source for this sound has long been unclear, until detailed research revealed the exact mechanism (2 Clark, C.J., Kirschel, A.N.G., Hadjioannou, L. and Prum, R.O. (2016). Smithornis broadbills produce loud wing song by aeroelastic flutter of medial primary wing feathers. Journal of Experimental Biology 219: 1069–1075. Close ).

Vocal Development

No information.

Vocal Array

Song. See below under nonvocal sounds.

Eeeuw. A somewhat nasal plaintive whistle, downslurred or nearly flat-pitched. Duration 0.5‒1.0s, fundamental frequency c 2kHz.

Tueet. A faint plaintive upslurred whistle, sometimes preceeded by a shorter note "tu-tueet". Uttered either single or in series. Duration c 0.25s, pitch rising from about 2 to 3kHz. This whistle can also be heard in combination with the "Eeeuw" call, and is also uttered sometimes during display.

Other. A loud klaxon-like noise produced by primaries when hanging from perch in courtship display, and said to be different from the mechanical display song has been described (3 Lawson, W.J. (1961). Probable courtship behaviour of the Broadbill Smithornis capensis. Ibis. 103a: 289-290. Close ), but has not been documented more recently.

Geographic Variation

The mechanical display sound has been transcribed in many different ways, suggesting possible geographical variation (4 Lambert, F. R., and M. Woodcock (1996). Pittas, Broadbills and Asities. Pica Press, Robertsbridge, UK. Close ). Sound recordings from locations spread over its entire range don't seem to support this however, and on the contrary suggest very little variation in mechanical display song among the many races. "Eeeuw" calls from Tanzania and Zambia show some differences but available sound recordings are too few to draw firm conclusions.

Phenology

Zimmerman (5 Zimmerman, D. A. (1972). The avifauna of the Kakamega Forest, western Kenya, including a bird population study. Bulletin of the American Museum of Natural History 149(3):255–340. Close ) reported that in Kakamega forest, Kenya, display flights are rarely observed outside the breeding season, although Brosset and Erard (6 Brosset, A., and C. Erard (1986). Les Oiseaux des Régions Forestières du Nord-est du Gabon. Volume 1. Écologie et comportment des espèces. Société Nationale de Protection de la Nature, Paris, France. Close ) found this species displaying year round in Gabon. In Zambia they were noted in most months, but less frequent during the dry season (7 Dowsett, R. J., D. R. Aspinwall, and F. Dowsett-Lemaire (2008). The Birds of Zambia. Tauraco Press & Aves, Liège, Belgium Close ).

Daily Pattern of Vocalizing

Display starts pre-dawn, and the mechanical rattle is one of the first sounds heard at the onset of the dawn chorus. Frequency of display flights is typically high in early morning, after which activity diminishes, but its sound can be heard at any time of the day. "Tueet" and "Eeeuw" calls can be heard during the morning, often in combination with the display flight. "Eeeuw" calls alone are also often heard late at dusk, in near darkness.

Places of Vocalizing

Males display from a perch at a height of 1‒15m. Such perches are near horizontal bare branches, with a diameter of about 2‒4cm.

Sex Differences

Mechanical display song is only performed by males (2 Clark, C.J., Kirschel, A.N.G., Hadjioannou, L. and Prum, R.O. (2016). Smithornis broadbills produce loud wing song by aeroelastic flutter of medial primary wing feathers. Journal of Experimental Biology 219: 1069–1075. Close ), contrary to earlier assumptions (8 Chapin, J. P. (1953). The birds of the Belgian Congo. Part 3. Bulletin of the American Museum of Natural History 75A:1–821. Close ).

Social Content and Presumed Functions of Vocalizations

The mechanical display song is thought to have a function both for territorial defence and mate attraction, respectively based on male's response to play back and the occasional interest by females (2 Clark, C.J., Kirschel, A.N.G., Hadjioannou, L. and Prum, R.O. (2016). Smithornis broadbills produce loud wing song by aeroelastic flutter of medial primary wing feathers. Journal of Experimental Biology 219: 1069–1075. Close ).

Territorial song of this species is a sound emitted during a short display flight in which the male bird performs an elliptical or circular trajectory from a fixed perch, landing where it began (flight duration c 1s, trajectory c 0.5‒0.8m in diameter). The sound is a loud rattling claxon-like croak "k-k-krrrrrrrk", starting with 1‒3 slower pulses when taking off and followed by a faster rattle (pace 28.6±1.3 pulses/s, fundamental sound frequency c 0.8kHz and a total of approx. 25 pulses), often with some modulation in amplitude over the course of the rattle. Display flights are repeated on average every 20-45s, sometimes for over a dozen times, before moving to another perch. Recent wind tunnel experiments revealed that the sound is generated by aeroelastic fluttering of the primaries p5, p6 and p7 (contrary to earlier beliefs that the sound was either vocal or made by the outer primaries)(2 Clark, C.J., Kirschel, A.N.G., Hadjioannou, L. and Prum, R.O. (2016). Smithornis broadbills produce loud wing song by aeroelastic flutter of medial primary wing feathers. Journal of Experimental Biology 219: 1069–1075. Close ). This song can be heard over a long distance of about 60‒100m. Over the course of a day males perform hundreds such display flights, suggesting this requires little physical demand.

Season probably long, at least 6 months, in W & C Africa, with breeding recorded in Feb–Apr in Liberia, Mar–Jul in Cameroon, Dec–Mar in Angola, Jan and Aug in Gabon, Sept–May in E Zaire; in E & S Africa, laying tends to begin with the rains, e.g. breeds mainly in Oct–Feb in Malawi and Zimbabwe, but to as late as Mar in Kenya and Apr in Zambia, and in Dec in Mozambique and Oct–Feb in South Africa. Nest a bag of plant fibres, dead leaves, green moss and twigs with untidy hanging “tail”, slightly porched entrance high on side, lined with soft bark, dry stems, leaves and grasses and matted together with spider silk, but some geographical variation in materials used, which can include fine black fungal strands of Marasmius, long fibrous bark and dried plant stalks, and some nests in S Africa made entirely of “old man’s beard” lichen; nest attached to thin horizontal branch c. 1–2·5 m above ground in bush, small tree or sapling in dense, shady understorey, rarely in more open situations. Clutch 1–3 eggs, usually 2–3; incubation and the care of chicks unrecorded, likely to be much as for S. rufolateralis. A nest in Zimbabwe contained 3 eggs, 1 of which was identified as probably having been laid by a Barred Long-tailed Cuckoo (Cercococcyx montanus).

Not globally threatened. Locally common in much of its range, but becoming scarce in many areas and disappearing from others. Present in several protected areas. In S Africa, rare or very scarce in Botswana, Swaziland and South Africa. Rare in Togo and Gabon; rare or under-reported in Liberia. In Kenya, has disappeared from areas E of the Rift Valley, from Mt Kenya and the Ngaia Forest S to Nairobi suburbs and Chyulu Hills, and now considered rare. Also scarce in Tanzania and Mozambique, but can be locally common in suitable areas. A study in the Kakamega Forest, in W Kenya, found its population density to be very low for a bird of its size, with 1 adult in 8 ha of forest, suggesting around 12 birds/km². In E & S Africa, this species’ rarity is attributed to habitat destruction and it is considered vulnerable in many areas.