Evidence of co-operative breeding by white-bellied go-away birds (Corythaixoides leucogaster)
White-bellied go-away birds (Corythaixoides leucogaster Rüppell) are highly social open-country turacos that forage and roost in loose groups of three to twelve individuals during the nonbreeding season (Brosset & Fry, 1988; Turner, 1997). Several birds often forage in the same tree or adjacent trees, calling back and forth in loud exchanges that may last up to several minutes. Such calling bouts presumably serve to keep group members in contact with one another, particularly when they assemble at roost sites. These aggregations are often referred to as ‘family groups’ (Stevenson & Fanshawe, 2002) and are assumed to consist of a breeding pair and several retained offspring; however, the group composition has not been studied.
Irvine (1977) reported one instance of helping behaviour in a family group of white-bellied go-away birds, in which an extra-pair adult was observed delivering food to an immature, but it appeared to be an isolated occurrence. As a result, Ligon & Burt (2004) did not include the white-bellied go-away bird in their global list of co-operatively breeding bird species, listing it instead as one in which helping behaviour was either so infrequent as to be negligible or was ‘accidental misdirected care.’ This classification, however, may simply reflect a dearth of natural history data.
In this note, I document repeated helping behaviour by extra-pair males in two broods of white-bellied go-away birds. Each brood consisted of one fledgling, which was fed by one adult female and two different males. Although preliminary, these data suggest that helping behaviour may occur more frequently than is now recognized. If so, the presence of extra-pair helpers may partly explain the highly social nature of this species.
Materials and methods
I observed two family groups of white-bellied go-away birds at Mpala Research Centre (MRC), Laikipia, Kenya (0°17′N, 37°52′E). MRC is characterized by semi-arid savanna woodland, dominated by Acacia and Euphorbia spp. Rainfall is seasonal; annual precipitation is 300–600 mm year−1. Observations were made during the dry (nonbreeding) season. White-bellied go-away birds are sexually dimorphic; the male's bill is black, while the female's is greenish.
Both groups held consistent roosting sites, so group composition was determined by counting the number of individuals present at the roost at dusk and dawn each day. Both groups consisted of one recently fledged (immature) male, one female and a variable number of males. Between two and four males roosted at the group 1 site; between four and seven males roosted at the group 2 site. Immature birds had fledged approximately 1 month prior to the study period (W. Watetu, personal communication). The roosting sites of the two groups remained constant during the study and were separated by approximately 0.6 km.
Both groups were well-habituated to people and frequently fed in Acacia etbaica Schweinfurth trees around the MRC facilities, allowing close observation (often within 6 m). In addition, most birds had extensive damage to the retrices and primary feathers, allowing identification of many individuals through unique combinations of sex, age and tail and wing feather damage. Males and females were differentiated by bill colour; fledglings were identified by begging behaviour, fleshy gapes, fuzzy head feathers and brownish feathering on the back and upper wing coverts.
I observed the two groups on alternating days between 3 Jan and 21 Jan 2006, resulting in 91 h of field observations of group 1 and 102 h of group 2. Groups were tracked on foot by following immature birds while they foraged. When immatures were fed by other individuals, I recorded the sex and identity of the adult bird, and the species of the plant being delivered.
Results and discussion
Immature males were capable of foraging independently, but frequently begged from nearby individuals. In both family groups, the immature was fed by three different birds: the female, a ‘primary’ male that was responsible for the majority of deliveries and a ‘secondary’ male that delivered food less often (Table 1). Both males in group 1 were adult-plumaged; however, the primary male was missing three rectrices and was easily distinguished from the secondary male. In group 2, the secondary male still retained several brownish feathers in the upper wing coverts, indicating that it had recently molted the juvenal feathers. The primary male delivered food significantly more often than either the secondary male or the adult female (group 1: χ22 = 17.05, P < 0.0001; group 2: χ22 = 14.69, P < 0.0001). In both groups, the primary male always roosted with the adult female and immature male, suggesting that the primary male shared a pair-bond with the adult female. In neither case was it possible to determine genetically which male had sired the fledgling; however, the secondary male in group 2 was not in full adult plumage, suggesting that the primary male was the father of the fledgling. Acacia etbaica flowers accounted for the majority of deliveries to both fledglings; the flowers of Acacia mellifera Bentham and the fruits of Balanites aegypticus Wall, Cyphostemma serpens Descoings, Euclea divinorum Hiern and Boscia angustifolia Harvey were delivered less often (Table 2).
Table 1. Number of times that adult male and female white-bellied go-away birds were observed delivering food to fledglings in two different family groups. The fledgling in each brood was fed by two males and one female (group 1: n = 67 food deliveries; group 2: n = 41 food deliveries)
|Group 1||38 (56.7)||12 (17.9)||17 (25.4)||67 (100)|
|Group 2||25 (61)||10 (24.4)||6 (14.6)||41 (100)|
Table 2. Food items delivered to fledgling white-bellied go-away birds in two family groups
|Leguminosae||Acacia etbaica (flower)||48 (71.6)||24 (58.5)|
|Leguminosae||Acacia mellifera (flower)||9 (13.4)||1 (2.4)|
|Balanitaceae||Balanites aegyptica (fruit)||7 (10.4)||1 (2.4)|
|Vitaceae||Cyphostemma serpens (fruit)||3 (4.5)||6 (146)|
|Ebenaceae||Euclea divinorum (fruit)||0 (0.0)||3 (7.3)|
|Capparaceae||Boscia angustifolia (fruit)||0 (0.0)||6 (14.6)|
|Total|| ||67 (100)||41 (100)|
The evidence presented in this study, though limited, suggests that helping behaviour may be more common in white-bellied go-away birds than previously suspected. Population-wide co-operative breeding has been documented for a congener, the grey go-away bird (Corythaixoides concolor Smith; Du Plessis, Siegfried & Armstrong, 1995). This may be relevant as co-operative breeding is often conserved within a genus; in fact, phylogenetic history is the best predictor of co-operative breeding within a taxon (Edwards & Naeem, 1993; Ligon & Burt, 2004). In addition, the white-bellied go-away bird appears to exhibit some of the behavioural and life-history traits associated with co-operative breeding: it forms stable flocks, holds group territories during the nonbreeding season and inhabits a highly seasonal environment in which patchy resource distribution may constrain reproduction (Stacey & Ligon, 1991). Longer-term demographic studies of colour-banded individuals are needed to better clarify the social structure of this locally common but little-studied species.
I thank Daniel I. Rubenstein, Dustin R. Rubenstein and Wilson Nderitu Watetu for their invaluable advice and assistance.