Condor 85323-332 0 The Cooper Omithologlcal Society 1983 A REVIEW OF DUETTING, SOCIALITY AND SPECIATION IN SOME AFRICAN BARBETS (CAPITONIDAE) LESTER L. SHORT AND JENNIFER F. M. HORNE ABSTRACT.-Our East African studies have focused on the sociality, duetting and intra- and interspecific systematicsof barbets (Capitonidae). The Afrotropical barbets include 14 duetting, social speciesand 22 non-duetters, both social and non-social. In this review of them, comparisons are broadly conducted, but cen- tered about the ground barbets (Trachyphonus) and some speciesof Lybius. The sexually dichromatic Red and Yellow Barbet (T. erythrocephalus)occurs in pairs and in social groups; duetting is by the pair, or mainly by the primary pair of a group. Within groups, secondary adults and young may join in part of the duet but their roles are limited by the dominance of the primary pair. The sexual songs are not very different. Subspeciesof erythrocephalusdiffer little morphologically except in color tone and size. Darnaud’s Barbet (T. darnaudii) is sexually monomorphic with racesmorphologically somewhat divergent. Sexual duetting roles are distinctive, and in groups the primary pair actively prevents duetting of secondaryadults or young birds. Removal of a duetter leads to instant replacement from within the group, another bird assuming the duet role of the lost bird. In the Red-faced Barbet (Lybius rubr$zcies), the Black-collared Barbet (L. torquatus) and the Black-billed Barbet (L. guifsobalito) the sexes are alike, pairs and social groups occur, and duetting is by the primary pair, with distinct sexual duet roles, following a greeting ceremony in which other individuals may take part. Secondary “pairs” occur in some groups; these may duet when apart from the primary pair, but not in the presenceof the latter. Allopatric torquatus and guifsobalitoshow no or modest geographicvariation and have similar though distinctive duets. Lybius rubrifaciesshows no morphological geographicvariation, and marginally overlaps torquatus;its duet markedly differs from that of torquatus. The duet songs, whatever the degree of genetic control, are species-specific. Only paired duetting birds hold territories. Systematic comparison and studiesof sociality and duetting in Afrotropical barbets suggestthat the nature of their social systemsand their duets, where these exist, has affected their speciation, and vice versa. Duet-singing in birds can be intricately timed the genetic basesand experiential background and complex (Thorpe 1972, 1973). Duets are that go into precisely timed duetting songs(Ty- usually between paired birds and may be pre- roller 1974). It seemslogical that the evolution cisely alternating (antiphonal), or in unison of speciesin avian groups that are social and (polyphonic). Unison-singing may simply be regularly duet has been affected by their so- the simultaneous singing of two birds at their ciality and duetting habits. More particularly, own individual rhythms with overlapping the ability of individuals of one population to songs, or more precise singing together in a duet appropriately-and hence to pair with in- coordinating rhythm. Additionally, the songs dividuals of another population-ought to be of the duetters may be identical, they may dif- of importance in relation to speciation. Gen- fer somewhat, or may be strikingly different. eralizations must be tempered, however, by These categoriesof duetting are modified here the fact that each avian species has its own from those of Thorpe (1973). unique distribution, ecology, history, and par- Although the relative importance of the dif- ticular relations with congeneric, distantly re- ferent functions of duetting is arguable (Wick- lated, and even unrelated sympatric species. ler 1976) the complexity and coordination of We have studied various Afrotropical bar- many duets clearly shows close interplay be- bets in the field, devoting attention especially tween the duetters. Studies of the development to their sociality, vocal habits and related be- of duets in young barbets also indicate the havior. Barbets generally are aggressive,om- complex nature of duets. Such works suggest nivorous or fiugivorous, hole-nestingand hole- 13231 324 LESTER L. SHORT AND JENNIFER F. M. HORNE TABLE 1. Duetting features of barbets Stactolaemaolivacea 0* 0 pitch mainly occasionally Lybius melanopterus 0 0 0 Lybius leucocephalus A 0 0 + & Lybius vieilloti + 0 pitch + 0 Lybius rubrifacies + f +++ 0 + Lybius torquatus + 0 ++ 0 + Lybius guifsobalito + 0 ++ 0 + Trachyphonusmargarita&s + 0 + 0 + Trachyphonuserythrocephalus + 0 + 0 + Trachyphonusdarnaudii + 0 +++ 0 + * 0 mdlcates absence, + prescncc:in the third column the plusesmdlcate the degree of difference III form (+, some d~lTerence, to +++. vev marked deference). Parentheses mean that the data are not concluswe or certain for all subspecies. roosting, sedentarypiciform birds. The species Tape recordingswere made by Horne using we have investigated in some detail that form a Stellavox SP-7 recorder, 72-cm parabolic re- the subject of this article are: the Green Barbet flector, and Schoeps CMC-45 microphone, (Stactolaema olivacea, Short and Horne with playback conductedby Short usinga Sony 1980b); the White-headed Barbet (Lybius feu- cassette recorder. Audiospectrographic anal- cocephalus,two subspecies;unpubl. data); the ysis involved use of a Kay Elemetrics Sona- Black-billed Barbet (L. guifsobalito; unpubl. Graph 6061B to produce about 2,500 sono- data); the Black-collared Barbet (L. torquatus; grams of voices of the barbets discussed.The Short and Horne 1982); the Red and Yellow various analyses took place in the American Barbet (Trachyphonus erythrocephalus;Short Museum of Natural History. and Horne 1980a, in press); and Darnaud’s Barbet (T. darnaudii, three subspecies;Short DUET FUNCTION, SEASONALITY, and Horne 1980a, in press). Fewer details are AND THE DUETTERS available from our less extensive (Short and Duetting barbetsare sedentaryand they clearly Horne, unpubl. data) studies of the Brown- employ the duet in territorial defense and breasted Barbet (L. melanopterus), the Yel- maintenance.At a distance,only the loud notes low-billed Barbet (T. purpuratus) and the of the duet can be heard, and thus they can be Crested Barbet (T. vaillantii). We also have effective in those functions. Only at rangesup been supplied by C. Chappuis with tape re- to 20 or 30 m are the pre- and post-duet notes cordings of duets of the Vieillot’s Barbet (L. and the softer duet notes audible to humans, vieilloti; Payne and Skinner 1970) and the Yel- and presumably to the duettersthemselves and low-breasted Barbet (T. margaritatus; Short to any members of their group closely asso- and Horne, unpubl. data). The duetting fea- ciated with them. This suggeststhat these soft- tures of thesebarbets are summarized in Table er notes function in pair relations and pair 1. Our field researchesmainly have been in maintenance. Kenya for several months of each of the years Duets are uttered to some extent the year- 1976-1982; the Red-faced Barbet (L. rubri- round, although lessfrequently when the birds facies) was investigated in Rwanda during Jan- are not breeding. Duetters, as well as other uary 1982. members of a barbet group, even including Ecological, distributional, morphological, subadults, have enlarged gonads all year (go- social and vocal information on the African nads over 2.5 mm in diameter, pers. observ.). barbets mentioned above forms a background Individual barbets of duetting speciesdo not for consideration of the interrelationship singalone; when one bird rarely does so under among their sociality, form and complexity of exceptional circumstances,it singsonly its par- singing,and evolution, particularly speciation. ticular duet song,and that haltingly. Thus, the In this paper we treat Lybius and Trachy- singingof these barbets is virtually entirely in phonus in special detail, as their species are the form of duets, and in most speciesthese widespread and vary interspecifically and in- are uttered only by the primary pair. Dar- traspecificallyin the parametersjust noted. The naud’s Barbets who are members of a group ecologyand sociality of duetting and non-duet- other than the duetting pair are prevented by ting barbets are compared. Within this frame- aggressiveactions of that pair from duetting work we explore the possibleeffects of specia- (Short and Horne 1980a). In groups of Lybius tion on the occurrence and complexity of rubrifacies and L. torquatus, sub-pairs (pairs duetting in the African barbets. other than the primary pair) occasionallyduet. BARBET SOCIALITY 325 However, they do so only in the absenceof the “moderate” response,reacting either to play- primary pair, which if within hearing, usually back or to actual duets of a related duetting approach the sub-pair, causing them to cease species by some approaching and mainly duetting. Singlebarbets in the wild do not utter counter-duetting (seeLybius rubrifaciesand L. both duet parts. The duets sungby the pair are torquatus, below). So far in our researches, crucial for the establishment and holding of a however, very close,instant and consistentap- territory. Hence, a barbet is likely to maintain proaches to a playback duet (i.e., a “strong” a territory, and to breed, only if it finds a duet response), followed by search behavior and partner of the opposite sex and the two manage counter-duetting mark only conspecific inter- to synchronize their duet. actions. For example, this occurs among sub- The non-duetting