Berkut. Vol. 13. Is. 2. 2004. P. 258-261.

 

 

CALL FUNCTION AND VOCAL ACTIVITY IN THE SOUTHERN BALD IBIS AT A BREEDING SITE

 

Grzegorz Kopij

 

Abstract. Studies were carried out in a breeding colony at Welgelegen, eastern Free State, South Africa in 1994. Seven different calls in the Southern Bald Ibis were distinguished and their function has been determined: ‘clangor’, alarm, barking, copulation, snoring, greeting and begging. In the pre-laying phase, breeding and non-breeding pairs were equally vocal. Among breeding birds females were more (60.0 %) vocal than males (40.0 % of 402 calls recorded), while among non-breeding paired birds the reverse was true (males: 57.5 %, females: 42.5 %; n = 134 calls recorded). At the nest, breeding birds were more vocal during the incubation than during the pre-laying and nestling phases, while non-breeding paired birds are more vocal at the beginning of the breeding season than latter. During the day, breeding birds are more vocal in the morning (7⁰⁰–10⁰⁰; 40.5 %), while non-breeding paired birds are more vocal around the noon (10⁰⁰–14⁰⁰; 50.6 %) and in the evening (16⁰⁰–18⁰⁰; 23.4 %).

Key words: Southern Bald Ibis, Geronticus calvus, South Africa, vocalization, vocal activity.

Address: Department of Zoology & Ecology, Agricultural University of Wrocław, ul. Kożuchowska 5b, 51-631 Wrocław, Poland.

 

Функции криков и вокальная активность у лысого ибиса в местах гнездования. - Г. Копий. - Беркут. 13 (2). 2004. - Исследования проводились на одной из гнездовых колоний в Велгелегене на востоке Оранжевого Свободного Государства в ЮАР в 1994 г. Было выделено 7 различных криков и определена их функция: тревога, копуляция, приветствие, выпрашивание и др. Перед откладкой яиц вокальная активность гнездящихся и негнездящихся птиц примерно одинакова. Среди гнездящихся птиц более активно вокализируют самки (60,0 %), чем самцы (40,0 %, n = 402), среди негнездящихся – самцы (57,5 %, самки: 42,5 %; n = 134). На гнезде гнездящиеся птицы более крикливы во время насиживания, чем до откладки яиц или при выкармливании птенцов. Неразмножающиеся пары более активно вокализируют в начале гнездового сезона, чем позже. На протяжении дня гнездящиеся птицы больше кричат утром (7⁰⁰–10⁰⁰; 40,5 %), негнездящиеся – около полудня (10⁰⁰–14⁰⁰; 50,6 %) и вечером (16⁰⁰–18⁰⁰; 23,4 %).

 

INTRODUCTION

 

Ibises (Threskiornithinae) are a cosmopolitan ciconiifrom subfamily of 32 species found mainly in the tropics (Del Hoyo et al., 1992). In the Afrotropical region, there occur eight ibis species (Dowsett, Forbes-Watson, 1993) associated usually with lowland wetlands. Most of these species are gregarious both while feeding and at nesting sites. The extend of social tendency varies, however, from species to species. Threskiornis is strictly colonial, Geronticus and Plegadis are less so, and Bostrichia is actually a solitary breeder (Brown et al., 1982). Because of gregariuos habits, most ibis species should be vocal, but they are in fact rather silent as their vocal apparatus is not well developed.

Among ibises occurring in Africa, the Southern Bald Ibis (Geronticus calvus) is especially interesting. Unlike most other members of the order Ciconiiformes it breeds in monospecific colonies, not on trees but on sandstone cliffs. Unlike other members of the order it is also not directly associated with wetlands and it inhabits mountain grasslands and farmlands. It is silent while feeding, but vocal in breeding sites.

Behaviour of this species in breeding sites has been thoroughly investigated in its stronghold in the eastern Free State (Kopij, 1998b; Kopij et al., 2000). Its breeding display, agonistic, anti-predator, comfort and parental behaviour were found to be highly developed and complex, and it is often accompanied by specific vocalization (Kopij 1998a). Although, the Southern Bald Ibis behaviour is well documented, little is known about vocalization in this species. Brown et al. (1982) listed seven different calls, but these calls are not fully described and their function is not always well explicit. The purpose of this study was to analyse at breeding sites, the function of the Southern Bald Ibis calls, daily and seasonal vocal activities between male and female, between parents and offspring and between non-breeding and breeding pairs.

 

STUDY SITE

 

Studies were carried out at a colony situated in a gorge, 7 km north of Clarens in the eastern Free State (28°30' S, 28°20' E), South Africa. The gorge is narrow (c. 10–20 m), but deep (c. 80 m), with a small stream flowing through it. As the gorge is closed on three sides, the stream flowing into it forms a narrow waterfall. There is a small (c. 30 m²) but quite deep (2 m) pool at the point where the gorge broadens. Further on the gorge is much broader, forming a valley vegetated with trees (mainly Grewia occidentalis, Leucosidea sericea, Populus tremula and Salix babylonica). The gorge is bordered on one side by mountainous highveld grassland utilised as pastures for cattle and sheep, and on the other by cultivated fields with maize as the main crop. A dam is situated 3 km north of the gorge.

The Southern Bald Ibis colony was occupied by 23 breeding and seven non-breeding pairs, and later in the season (after 5 September), seven immature birds remained in the colony. Five other nests, built on sandy rock ledges, were located out of the gorge 100, 200, 400 and 500 m away from the main colony. The nest under detailed observation was already occupied by a pair on the first day of the study. The first egg was laid on 4 August, the second on 8 August and the third on 10 August, while the first nestling hatched on 1 September, the second on 3 September and the last on 5 September. The youngest chick died at age 5 days and the next one at age 12 days; the oldest (when 35 days old) was killed by a Black Eagle (Aquila verreauxii) (Kopij, 1995).

 

MATERIAL AND METHODS

 

Studies on the behaviour of the Southern Bald Ibis were conducted at the Welgelegen colony during the breeding season, from 2.07 until 4.10.1994 (Kopij et al., 2000). Two nests were under detailed week-to-week observations; the first one was occupied by a breeding pair, while the other one by a non-breeding pair. Observations, using 10 x 50 binoculars and a Panasonic TTL 200 mm video camera, were made from a shelter built on a rocky outcrop on the opposite cliff at a distance of 15 m from the first and 20 m from the second nest. The shelter was entered without any disturbance to the birds.

Observations at the two nests were standardised and were carried out on a weekly basis from 21 July until 4 October 1994; i. e. 21 and 27 July (pre-laying phase); 4, 11, 18, 25 and 30/31 August (incubation phase), 6/7, 13/14, 20/21, 27/28 September and 4 October (nestling phase). On 27 July and 4, 11 and 18 August both nests were under detailed observation. Since the nest of the non-breeding pair was occupied only occasionally after 30 August, observations on it were stopped. From 21 July to 25 August, studies were conducted throughout the day (6⁰⁰–18⁰⁰), whereas latter on, observations in the morning (6⁰⁰–12⁰⁰) and afternoon sessions (12⁰⁰–18⁰⁰) were carried out on alternate days (vide Kopij et al., 2000).

Most call notes were kept in the form of time-scores (for each 15 minute period). There is no sexual dimorphism in the Southern Bald Ibis. Sexes were distinguished in the nests by behaviour and by individual characters, e. g. marks on their foreheads or cheeks.

 

RESULTS AND DISCUSSION

 

Call function

Seven different calls were distinguished in this study: ‘clangor’, alarm, barking, copulation, snoring, greeting and begging.

The Clangor: ‘whee-okh, whee-okh, whee-okh ...’ A prelonged, flute-like call, somewhat resonant, usually given by birds arriving or departing the breeding colony. This call most probably encourages other birds to leave the colony.

The alarm call: ‘peeokh’. It sounds like a short version of the clangor. At breeding site, it was heard most often at the beginning of the incubation phase (i. e. 11–18 August; 77 % of all records of this call; Fig. 1). During the day, the call was recorded mainly between 10⁰⁰ and 13⁰⁰ (61 %) and between 16⁰⁰ and 18⁰⁰ (27 % of all alarm calls recorded). The call was uttered to warn other birds about a potential predator, including human, and during communal mobbing of the Black Eagle (Kopij, 1995).

The barking call: ‘ek-ek-ek...’ Heard only at nesting sites, and mainly during the nestling phase (Fig. 1 and 2). It probably strengthen the bond between parents and between parents and their chicks, as the call is most often uttered as a reaction for chick’s call and during preening of adult birds (Table). Different number of syllables recorded in the call may indicate different motivational stages of the signallers (Table). The male and female differ slightly in this regard (Table). This call mixed with growls and moans was also distinguished in the invitation call. The so called ‘croop’ call of the Northern Bald Ibis (Geronticus eremita) is probably homologous to this call. Pegoraro and Foger (1995) studied intraspecific variation in this call and evidenced sexual and individual distinctiveness of this call indicating its function as an expression of motivational stages of the signaller.

 

The relationship between the number of syllables in the Southern Bald Ibis barking call and its function

Связь между количеством слогов в лающем крике лысого ибиса и его функцией

 

Situation/sex	Mean	Range	N	%
Response to chick’s call	4.2	1 – 10	10	8.6
Preening	3.4	1 – 8	20	17.2
Resting	3.3	1 – 7	66	56.9
Other situations	2.8	1 – 5	20	17.2
Male	3.4	1 – 10	61	52.6
Female	3.0	1 – 8	55	47.4

 

 

The copulation call: ‘ekekekekekekek...’ It is a prelonged version of the barking call, composed of dozen or so quick repetitions of the ‘ek’ syllable. It is uttered by female, 3–6 seconds after being mounted by male during the copulation.

The snoring call. It consists of growls and moans. Uttered during the back-biting ceremony and other agonistic interaction (cf. Kopij, 1998a). This call was also recorded in older chicks during fighting with younger siblings.

The greeting call; a mixture of different calls, with growls and moans being most often heard. This call is delivered during the invitation ceremony (cf. Kopij, 1998a) by the bird which has remained in the nest; the arriving bird remained silent during this ceremony.

Begging call: a long persistent chirrup ‘shreeeee’ uttered by chicks in discomfort situations, e. g. hunger, cold, heat.

No mechanical sounds, e. g. bill-clapping, rattle or clatter were recorded both in adult birds and chicks. According to Brown et al. (1982) bill-snapping is performed by both sexes during the copulation.

 

Vocal activity

In the pre-laying phase, breeding and non-breeding pairs were equally vocal; 104 calls were recorded for a breeding pair during the 16 hours of observations (i. e. 6.5 calls per hour) were uttered by a non-breeding pair.

Among breeding birds females were more (60.0 %) vocal than males (40.0 % of 402 calls recorded), while among non-breeding paired birds the reverse was true (males: 57.5 %, females: 42.5 %; n = 134 calls recorded). Breeding females are more involved in incubation and brooding, spending more time in the nest than the male (Kopij et al., 2000), while non-breeding male and female spend the same amount of time in the nest.

The vocal activity of parents and chicks was held on similar level throughout the nestling phase. During 54 hours of observations, 124 calls of single parent and 243 calls of two chicks were recorded (Fig. 1).

At the nest, breeding birds were more vocal during the incubation than during the pre-laying and nestling phases, being especially vocally active during the egg-laying and early incubation phases (Fig. 1). At these stages the vocalization may strengthen the pair-bond. Non-breeding paired birds are more vocal at the beginning of the breeding season than latter.

 

Fig. 1. Seasonal and daily vocal activity of breeding Southern Bald Ibises at a nesting site.  Black columns indicate adult birds, white – chicks; 1 – 21 July, 2 – 27 July, 3 – 4 August, 4 – 11 August, 5 – 18 August, 6 – 25 August, 7 – 30/31 August, 8 – 6/7 September, 9 – 13/14 September, 10 – 20/21 September, 11 – 27/28 September, 12 – 4 October (1–2: pre-laying phase, 3–7: incubation phase, 8–12: nestling phase).

 

 

During the day, breeding birds are more vocal in the morning (7⁰⁰–10⁰⁰; 40.5 %; Fig. 1), while non-breeding paired birds are more vocal around the noon (10⁰⁰–14⁰⁰; 50.6 %) and in the evening (16⁰⁰–18⁰⁰; 23.4 %; Fig. 2). Chicks are more vocal in mid-day (Fig. 1).

 

Fig. 2. Seasonal and daily vocal activity of non-breeding Southern Bald Ibises at a nesting site. 1 – 27 July, 2 –  4 August, 3 – 11 August, 4 – 18 August.

 

 

The present studies confirm general statements in the major textbooks on African birds (Brown et al., 1982; Del Hoyo et al., 1992; Maclean, 1993) that the Southern Bald Ibis is, as for an ibis species, very vocal at breeding colony throughout the breeding season. This could have developed under conditions where communally breeding birds had problems in visual contacts, as in some caves or hanging rock cliffs. Probable strong pair-bond could have also facilitated birds to be vocally active.

 

REFERENCES

 

Brown L.H., Urban E.K., Newman K. (1982): The Birds of Africa. Vol. 1. London: Academic Press.

Del Hoyo J., Elliot A., Sargatal J. (1992): Handbook of the Birds of the World. Vol. 1. Barcelona: Lynx Edicions.

Dowsett R.J., Forbes-Watson A.D. (1993): Checklist of birds of the Afrotropical and Malgasy regions. Liege (Belgium): Tauraco Press.

Kopij G. (1995): Black Eagle Aquila verreauxii predation on Southern Bald Ibis Geronticus calvus nestlings in South Africa. - J. Afr. Raptor Biology. 10 (1): 37.

Kopij G. (1998a): Behavioural patterns in the Southern Bald Ibis Geronticus calvus at breeding sites. - Vogelwarte. 39: 248-263.

Kopij G. (1998b): Breeding ecology of the Southern Bald Ibis Geronticus calvus in the Free State, South Africa. - Acta. Orn. 33: 99-111.

Kopij G., Kok O.B., Nuttall R.J. (2000): Breeding cycle of the Southern Bald Ibis Geronticus calvus. - Ostrich. 71: 393-399.

Maclean G.L. (1993): Robert’s birds of southern Africa. Cape Town: John Voelcker Bird Book Fund.

Pegoraro K., Fager M. (1995): Die ‘Chrup’-Rufe des Waldrapps Geronticus eremita: ihre verschiedenen Funktionen in einem komplexen Sozialsystem. - J. Orn. 136: 243-252.