I 06 BREEDING

the horizontal box once again. At th is point it was suspected that both ?? might be laying, although it was felt that one clutch would probably be infertile. As before, all three were seen only while feeding in the morning and evening. It is not known whether the 8 assisted in the incubation of either clutch, although he was seen entering both boxes during this period.

On 24 April the boxes were checked because food consumption indicated a large hatch. In the vertical box four chicks, approximately two- thirds grown, were found, while the horizontal box contained two more chicks, approximately one week old. Suspicions of a truly polygamous mating were thus confirmed.

By 21 May all four young conures from the vertical box had fledged but it was decided to leave them in the exhibit until they were self- sufficient. Some two weeks later all were feeding on their own and were removed. The two young from the horizontal box fledged on zs June and were also removed.

The trio of adults continued to produce young from both nestboxes during the remainder of the summer and autumn, giving a total of 13 young

for 1976. By the end of August 1977 they had produced seven additional young, all from the vertical box. It is uncertain whether both 99 laid eggs during this period; however, both were frequently seen entering the box along with the 8.

In a continuing experiment, three young conures from the first two clutches (two from the clutch of four and one from the clutch of two) were placed in an adjacent exhibit in the autumn of 1976. While the sex of these individuals is still unknown, some breedmg behaviour has been observedduring the following spring and summer.

If a situation can be created with captive-bred Sun conures which duplicates the polygamous relationship of the original breeding trio, then it might be hypothesised that t h i s may be aphenom- enon which occurs naturally in the wild.

PRODUCT M E N T I O N E D IN THE T E X T Zu/Preem Bud of Prey Diet: manufactured by Hill's Division Kviana Foods, Inc., POD 148, Topeka, Kansas 66601, USA.

Manuscript submitted 8 November 1976 (re- vised September 1977)

Co-operative breeding in the White-crested laughing thrush

with notes on its hand-rearing at Busch Bird Park, Houston

Garrulax leucolophus

RONALD A. Y O U N G ' Z o o Department Manager, Busch Bird Park, Houston, Texas 77029, USA

In July 1971 six newly purchased White-crested laughing thrushes Garrulax leucolophus were introduced into the freeflight aviary at Busch Bird Park in Houston. This is a walk-through exhibit, approximately 3000 ma in ground area and 23 m hgh, and is open to visitors all year round. Its dense subtropical planting offers protection to more than 50 bird species- protection not only from the drastic ff uctuations

of the Houston climate, but also from harassment by the public.

During the winter and spring of 1971-72, three of the birds died and in June 1972 six replace- ments were released into the aviary. At this point we were not aware of the aggressiveness of the species towards newcomers of its own kind, nor did we know that the three original birds had begun nesting. We learned quickly, however, as

'Present address: Busch Gardens, Tampa, Florida 33612, USA

BREEDING 107

w i h three days the s i x new birds were found dead, all apparently killed by the three senior residents.

AVIARY-REARED CHICKS On 16 April 1974 hopes of still having a breeding pair were confirmed when a new clutch of three all hatched. Knowing now that it was impossible

P I R S T C L U T C H E S

On 8 June 1972 four chicks were discovered in a securely constructed nest about 2 m above the ground in a Ligttstrcrm bush. Fed mealworms, crickets and cockroaches by all three adult birds, the chicks developed well. At the time we considered it strange that the ‘extra’ bird should assist in protecting the nest site and in feeding the young. We have since found in the four years of raising this species that its social structure is such that, regardless of how many adults in a given e h b i t , only a single nest is produced and only one 9 lays eggs. WMe only the breeding pair will incubate the eggs, all adults in the group help protect the nest site and feed the young.

All four chicks in this first nesting were lost because they left the nest before they could fly and were either eaten by larger birds or drowned in the stream. A second nesting in October of that year produced one chick from three eggs, which again left the nest too young and perished.

H A N D - R E A R E D C H I C K S

In the following spring a third clutch was hatched. This time all three hatchlings were removed on about the tenth day for hand-rearing. They developed well on a diet of mealworms Tenebrio and Zu/Preem Canned Feline Diet, a prepared meat diet, and within ten days were feeding on their own. Several other clutches were laid that spring and summer but heavy rains and other natural disturbances destroyed them. On I August 1973, however, two of three eggs hatched and these chicks were again removed on day 10 and hand-reared in similar fashion to the spring brood.

During the winter of 1973-74 one of the three adults was lost and, their sexes never having been clearly identified, we were uncertain as to whether we still possessed a pair. For this reason we made an attempt in March 1974 to introduce the five 1973-hatched juveniles into the exhibit. It was a failure, however, as the two adults immediately began to harass and attack the younger birds and eventually all five had to be withdrawn.

to introduce any more adults into the aviiry, we sought a method that would allow the chicks to remain with their parents and yet would keep them from drowning or falling prey to other species. Our chief concern was to ensure that, if one of the breeding birds were lost, there should beother adults in the e h b i t to continue reproduction.

To t h i s end we constructed out of 25’4 mm (I in) weldmesh a cage measuring 76 x 76 x 76 cm with access through a 15 x 15 cm door. This was fumished with branches and the three chicks, banded for identification, were shut in on the tenth day after hatching. With the cage positioned in a sheltered area of the aviary, the reaction of the adult thrushes were expectantly awaited. Our efforts were rewarded when we saw the parents carrying mealworms and feeding the chicks through the 25 mm openings in the mesh. The chicks remained in the ‘nursery’ cage for about 12

days, at which time the door was opened to let them fly fiee in the exhibit. At night they would return to roost on top of the cage with the parents. Although by now they were eating independently, they continued to beg and re- ceive food from the adults. With five compatible birds in the aviary, the prospects for continued breeding were more secure.

The presence of the three chicks apparently disrupted the reproductive cycle of the adult pair, for it was five months before they nested again. The single chick that hatched on 30 September from the three-egg clutch was taken for hand- rearing, as before. In the course of the next five months three nests were constructed and nine eggs laid but, with the cold rainy weather, the four chicks to hatch quickly perished. During 1975, however, five nests were constructed and 15 eggs laid; the 11 hatchlings were all hand- reared and all survived. Between January and April 1976 a further three clutches of the normal size produced six hatchlings, all of which survived by way of hand-rearing. Of particular interest were the actions of the 1974 chicks which had remained in the aviary with the parents. They assisted in nest construction and in pro- tecting and feeding the young, but only the two original birds laid eggs and incubated.

I08 B R E E D I N G

GROUP STRUCTURE

On 3 0 April 1976 an accident happened which was to reveal some particularly interesting aspects of the social behaviour of this species, The adult 8 escaped from the aviary through one of the public entrances and despite various attempts at recapture remained outside the e&bit for four months. During this period, on three occasions between June and August, the four birds inside the aviary constructed nests in various trees close to the wiremesh roof. At the same time the $. bird, hovering outside, would also build a nest, just above the one inside the aviary. In each instance the breeding 9 laid three eggs, and as she incubated them in the inside nest, the d outside would sit in his and perform all the motions of parental care. All nine eggs proved to be infertile, even though we were certain that at least one young 3 in the group was capable of fertilisation. These observations led us to conclude that our group of thrushes had developed a hierarchical structure, with dominant ~f and ? and three subordinate adult assistants. So powerful was the alpha ~ ' s dominance, that, even in the total absence of copulation between the bonded pair, hs presence was sufficient to prevent the 9 from accepting the attentions of a subordinate d.

During the last week in August the old cf was trapped and reunited with the group, giving rise to noisy chorusing and aerial display which continued sporadically throughout the day. Within two weeks a nest was constructed and two eggs laid which hatched on 10-1 I September. Heavy rains, however, destroyed the nest and both chicks were found dead a week later.

Another nest was started immediately and on 12

October three more eggs hatched, in our experience an exceptional occurrence as only 25 days had elapsed since the death of the previous chcks. Owing to an unseasond cold spell, the three hatchlings werc removed on day 7 and hand-reared in the usual manner; within 15 days they were feedmg independently.

Another three chicks were produced on 14 November, but with rain and a temperature of only I "C they died the next day. The last nest of 1976 was constructed between 22-27 November and four eggs laid between 28 November-3 December. Three of these hatched on 15 December, the fourth being infertile. All three chcks were removed on 27 December and suc- cessfully hand-reared as before.

S U M M A R Y

The following is a summary of observations on the social behaviour and nesting habits of the White-crested laughing thrush, as manifested in the five birds living as a group in the aviary at Busch Bird Park. The group is composed of one dominant pair, a subordinate 6 and 9 and one extra individual, believed to be a ?. Only the dominant pair has been seen mating and it alone produces eggs; the subordinate 'pair' have a bond of sorts, in that, when they are apart from the group, they will chorus in sequence, the 3 singing the higher pitched trills and the 9 the sharp harsh notes. All members of the group assist in nest construction and protection and in feeding the young, but only the breeding pair takes turns at incubation.

EGGS INPERTILE SURVIVED RBARBD TO YBAR NESTS LAID OR LOST HATCHED (7 days t) MATURITY

I972 2 7 2 5 5 I973 5 14 9 5 5 5 (hand-reared) I974 5 IS 7 8 4 4 (3 parent-reared,

I975 5 15 4 I1 I1 I I (hand-reared) 1976 I0 3 0 13 * 17 I12 12 (hand-reared)

Total 27 81 35 46 37 32

-

I hand-reared)

includes 9 infertile eggs laid during absence of breeding 8

Table I. Nesting record of the White-created laughing thrush Garrufar Zeucofophur at Busch Bird Park, Houston; all birds taken for hand-rearing survived to maturity.

BREEDING 1 0 9

The nest is cup-shaped, c. I 8 cm wide and I 5 cm deep, tightly woven of dried grass, light twigs and dead leaves. It is always securely intertwined amongst cIumps of bamboo and/or twiggy branches of shrubs or trees and is usually well concealed. So soundly is it constructed that on many occasions an abandoned nest has been taken over by other species such as rails, crakes or even touracos. Green vegetation and artificial materials such as string or paper, although available, are never utilised. Despite there being suitable nesting sites available as high as 9 m above the ground, all nests have been built between 0.6-2.4 m above ground level. A new nest is constructed for each nesting and is never closer than 6 m from the previous site; it is possible, however, that over the four-year period the same bush may have been used more than once.

Nesting has occurred in every month except February. The usual clutch consists of three eggs (range 2-4), with an average incubation period of 12 days. The fledging period is undetermined as chicks have normally been taken for hand- rearing on about the tenth day. Chicks reared by the adult birds are invariably fed live food, 90% of it mealworms. Hand-reared chicks have always been given and have thrived on a mixture of mealworms and a commercially prepared meat diet.

P R O D U C T M E N T I O N E D I N T H E T E X T Zu/Preem Canned Feline Diet: manufactured by Hill’s Division, Riviana Foods Inc., Topeka, Kansas 66601, USA.

E D I T O R ’ S N O T E

The social organisation of this particular group of laughing-thrushes. with its one breeding pair and one active nest, is almost certainly an atypical behaviour brought about by captive conditions. To-operative breeding’ (nest helpers and allied social phenomena) is characteristic of many species, including a number of dose relatives of G. leucolophur. Skutch (1935) first focused attention on birds whose nestlings were attended by individuals other than the two parents and 26 years later he produced a comprehensive survey (Skutch, 1961). Since then many more cases have been recorded; the sociological, ecological and evolutionary problem involved have been much discussed and formed the subject of one of the symposia of the 16th International Ornithological Congress held in Canberra in 1 9 7 4 , subsequently published in the Proceedings (Frith & Calaby, 1976) . Useful review papers covering most of the world were given by Rowley (Australian spp), Grimes (African spp), Woolfenden (American spp) and Zahavi (Eurasian spp).

REFERENCES FRITH, H. J, & CALABY, J. H. (eds) (1976): Proceeding3 of the 16th International Ornithological Congress Canberra: Australian Academy of Science. SKUTCH, A. F. (1935): Helpers at the nest. Auk 52: 257- 273. SKUTCH, A. F. (1961): Helpers among birds. Condor 63: 198-226.

Manuscript submitted I April 1977

Breeding a second generation of Common marmosets Callithrix jacchus

in captivity MIRANDA F. STEVENSON & ALISTAIR G. SUTCLIFFE Department of Zoology, University College of Wales, Aberystwyth SY23 3DA, Great Britain

No species of mammal can be said to have a truly successful captive record until a viable parent- reared second generation has been produced. This report details the successful breeding of second generation Common marmosets Callithrix jacchus and some of the problems encountered in their maintenance. The breeding of the second generation is of special interest in t h i s species owing to the role played by the father and older offspring in carrying and caring for the infants,

ANIMALS

Founder groups: The founder members of the colony and methods of maintenance are de- scribed in an earlier publication (Stevenson, 1976a). All four groups were formed from the initial pairing of two adults. All Aberystwyth born animals, with the exception of twins ‘Circe’ and ‘Titi’ whose mother died, remained in the family group till the next set of young were born, thus obtaining experience in carrying and