FREE MATE CHOICE IN CAPTIVE EAST AFRICAN CROWNED CRANES: A BEHAVIOUR STUDY AT LORO PARQUE

BY GUSTAVO SÁNCHEZ

AND DAVID WAUGH

The African crowned crane (Balearica regulorum) has a broad sub-Saharan distribution in the eastern and southern regions of the African continent (Johnsgard, 1983; Urban, 1983; Meine and Archibald, 1996). Despite being a familiar and widespread species, Meine and Archibald (1996) have suggested that it may well be vulnerable to increasing human disturbance, especially in the isolated marshy patches important for its breeding. Both subspecies are commonly kept in captivity and bred on a regular basis; for instance the International Zoo Yearbook in its most recent ten years of breeding census (to 1996) reported an average of 9.5 +/- 3.4 zoos breeding the nominate South African crowned crane, and 19.7 +/- 4.3 breeding the East African crowned crane (B. r. gibbericeps).

Despite the breeding record, this species and the West African crowned crane (Balearica pavonina) are frequently maintained in private and public collections seemingly for decorative purposes. This is acceptable if the birds are always well-kept, but it can result in less emphasis on using them for educational purposes, and often less effort to provide the necessary conditions for successful breeding. We believe that properly managed breeding is desirable and not prejudicial to decorative function. One obvious condition for successful breeding is to ensure the formation of compatible pairs, given that all crane species are strictly monogamous (Johnsgard, 1983). Even in collections with several individuals, where the age and health status of the birds, the husbandry regime and the conditions of housing should favour breeding, the record might be poor and could relate to forced pairing. Proximate signs of incompatibility, such as frequent mutual threat postures and little synchronization of activities within the pair, might not be especially evident.

In discussing pair-bonding in cranes, Derrickson and Carpenter (1983) indicate that they will usually choose a mate for life and that mate-swapping is very rare. Pair-bonding will normally occur in a situation of choice by the cranes. Derrickson and Carpenter further state that cranes will rapidly re-pair after the loss (death) of a partner, indicating the possibility to reorganise pairs within a single collection if the existing pairs are thought to be incompatible or poorly bonded. They also remark that stable homosexual pairs can occur in captivity. Unless two birds of known same sex have been put together for lack of other options, or for some other deliberate reason, this further emphasises the potential hazard of forced pairing coupled with the failure to identify the sex of the birds. Also referring to cranes in captivity, Swengel et al. (1996) mention that birds of similar age pair more readily. For the pairing of captive Balearica cranes, introducing them as they attain the full adult morphological characteristics at about 20 to 24 months (Johnsgard, 1983) would also be preferable. The foregoing remarks about how Balearica cranes are often kept in captivity imply that the ideal age mix might be infrequent.

The behaviour of cranes, especially that involved in forming and maintaining the pair bond, as well as defensive/territorial behaviour by the pair, is well-documented (Derrickson and Carpenter, 1983; Johnsgard, 1983; Swengel et al., 1996). Thus there exists a good base on which to identify pair formation by systematic observation of behaviour, whether this is of birds never before introduced to others as adults, or birds which are to be reorganised from their existing pairs or groups. Using simple systematic observation of selected behaviours, this brief study describes the formation of pairs of East African crowned cranes, where the birds have a choice of mates within a group.

All the East African crowned cranes in the Loro Parque collection were included in the study. They were identified by large white darvic, numbered leg-bands, and comprised five males (numbers 65, 66, 67, 68 and 69) and three females (numbers 93, 94 and 95). They were imported into the collection as adult birds, all pinioned, in March 1994. From this date until the pairing exercise in August 1996 they were maintained as an all-male group (65, 66, 68, 69) and a mixed group (67, 93, 94, 95) on two separated expanses of lawn in the park. No breeding attempts, nor any signs of pair-bonding, were previously noted in the mixed group.

Prior to putting all the birds together as one group, routine endoscopy on 29 August 1996 confirmed their sexes, and the reproductive organs demonstrated no sign of abnormality or senescence. The birds were introduced all at the same time to an enclosure measuring 18.5 ´ 15.0 m, with only one 18.5 m side fully exposed to park visitors. This northern aspect had a 2.75 m high barrier of flexible synthetic fibre string mesh, the southern side barrier had similar material but a finer mesh size, and the eastern barrier was formed by a palisade of off-view aviaries with fine weld-mesh, predominantly obscured by bushes and small trees. The entire 15 m of the western boundary was raised as a terrace 1.5 m above the rest of the enclosure, backed by a 5 m high artificial rock-work wall with occasional 0.5 m diameter openings screened with string mesh to a visitor pathway beyond. The enclosure had a fine gravel and sand/earth substrate, and was well planted with regularly spaced shrubs, bushes and trees providing shade, the possibility for birds to hide or escape from the attentions of others if necessary, and still the opportunity to observe them from each boundary. The cranes continued to be maintained with the same husbandry routine as before, following broadly accepted guidelines for the captive maintenance of cranes such as in Swengel and Carpenter (1996).

The group of cranes was observed from the time of its introduction to the enclosure on 30 August until 6 September 1996. On these days, observations were possible in the periods 10.30–13.00 and 15.30–18.00, thus totalling 40 hours.

The behaviours included in the study were grouped into those directly associated with pair formation and those denoting threat/aggression, as described by Johnsgard (1983) and Derrickson and Carpenter (1983). The former group comprised: head/body bobbing (rapid, jerky up and down movements); bowing (slow, forward tilting of the body in front of another individual); dancing (leaping into the air, with wings spread to varying extent); tossing object (an item from the ground thrown into the air with the beak); vocalizing (repeated call, usually in unison with another individual). The latter group comprised: raising tertials (this group of feathers raised from the body, usually also on the head and neck simultaneously); parade walking (stiff, deliberate steps passing one or more other individuals); ruffle-preening/false-preening (ritualized preening movements, often with feathers fluffed out at the same time); charging (arching of neck and restrained lunge towards another individual, sometimes with jabbing at the ground). These behaviours were recorded as all occurrences of separate events, or bouts of events where the same behaviour was performed several times in rapid sequence, and it was further noted whenever the same behaviour was performed simultaneously by two or more birds. All observations were recorded on data sheets.

Loro Parque, 28° 24´ N, 16° 13´ E and altitude 50 m a.m.s.l.,, has a dry sub-tropical climate. During the period of the study the prevailing weather conditions were sunny and warm with little cloud cover.

Within fifteen minutes of their introduction to the enclosure the cranes showed some threat behaviours, but during the study overall the level of aggression was not high (Table 1). Although males 66 and 67 showed higher incidence of threat behaviours than all other individuals, only one (no. 66) of these two eventually formed a pair. In fact, in neither males nor females could any significant difference in frequency of threat behaviours be demonstrated between the birds which formed pairs and those which did not (Mann-Whitney test, P > 0.05).

7 36 26 7 2 4 3 4

Within the first hours of introduction, the cranes were already showing behaviours clearly associated with pair formation, and by the second day there was strong demonstration of pair-bonding behaviours performed simultaneously. From this early stage, and reinforced throughout the subsequent days of observation, the simultaneous behaviours were carried out predominantly by male 65 with female 95 and male 66 with female 93 (Table 2), this frequency being significantly higher than for the birds which did not form pairs (Mann-Whitney test, z = 2.295, P = 0.02). It was evident that `bowing' behaviour was especially important in the formation of the pairs (Figure 1).

0 0 0 0 0 0 17 65

2 0 0 46 0 0 66

0 0 5 0 0 67

2 0 1 0 68

0 1 0 69

0 0 93

0 94

At the end of the eight days of observation, with evidently no further change in established behaviour patterns, the decision was taken to remove one pair to an adjoining enclosure (of similar size but, with far less vegetation, much more open in aspect) and the three unpaired males and female as a group to one of the original expanses of lawn. Further casual observations of this remaining group revealed no behaviours consistent with pair-formation.

This study shows that simple grouping and quantification of behaviours associated with pair formation in East African crowned cranes can be used effectively to identify pairs which result from the free mate choice possible in a group situation. The onset of these behaviours is almost immediate after the birds have been put together as a group, and the current study required no more than the eight days to establish that the formed pairs were stable, and that no exchange was likely to occur. Leaving all the birds together for a longer period might not have resulted in any higher level of aggressive behaviour, but a long-term grouping would be counter-productive to the ultimate objective of the pairing exercise because

breeding in captive cranes will not result unless conspecifics are removed from the same enclosure (Derrickson and Carpenter, 1983).

The occurrence of threat behaviours was not a directly useful indicator of pair formation in this study. It can be speculated that male 67 showed a higher incidence of threat behaviours as a residue of having been previously maintained for a long period of time with the females and no other males. His behaviours were directed towards male 66 and female 93 as they were forming a pair, probably explaining the much lower frequency of threat behaviours in male 65, and possibly even the fewer simultaneous pair-forming behaviours of 65 and female 95.

Swengel el al. (1996) point out that newly formed pairs of cranes are often ephemeral, and cannot be categorised as permanent until they have been stable for several months and/or breed. The two pairs formed in this study have subsequently been stable for 18 months. However, they did not breed in the 1997 breeding season for unavoidable reasons of disturbance associated with new exhibit construction in the park. With appropriate conditions established for 1998, it is hoped that these pairs will become successful breeders.

Thanks are due to Loro Parque for permitting access to make observations of the birds, and to the Loro Parque Fundación and its supporters.

Gustavo Sánchez, c/ Leopoldo Cologan Zulueta No. 16, Urb. La Paz, 38400 Puerto de la Cruz, Tenerife, Spain.

Dr David Waugh, Loro Parque Fundación, Avda Loro Parque, 38400 Puerto de la Cruz, Tenerife, Spain.

[As many readers of I.Z.N. will already have heard, in July this year David Waugh took over from Prof. Roger Wheater as Director of the Royal Zoological Society of Scotland (Edinburgh Zoo) – Ed.]