84 BREEDING

hatchlings scrambled to join the 9 lying in and calling from the poor. Subsequently the sixth egg was found to be infertile.

At 22 cm the hatchlings were surprisingly large; healthy Estuarine crocodiles Crocodylus porosus, the largest species, are not infrequently only this length at hatching (K.J.S., pers. obs.). The clutch size is the smallest viable crocodilian clutch known of by the authors, but is perhaps explicable as a first laying by a species known for small clutches (Cansdale, 1955). The five surviving hatchlings had rust coloured cranial tables and a mottling of red-brown patches on the black body colour. One was found dead on 10 September of unknown causes, post-mortem examination revealing that its yolk sac was incompletely absorbed; the remaining four thrived. A variety of insect food was left at the pool edge each evening and on 15 September fragments of the 7's food were seen to be eaten. From October onwards minced meat and young mice were eaten voluntarily. When out of the water the 9 was often joined by the hatchlings; neither of the $6 showed animosity towards them.

It is hoped that successful nesting will become an annual event and allow closer observation to be made of mating, nest building and incubation, and of the parental role in hatching and brood care.

ACKNOWLBDGBMENTS Thanks are due to the Malaysian Zoological Society for promoting the establishment ofthe breeding programme and for its encouragement in publishing these early results. The co-operation and interest of the Zoo Negara staff is appreciated.

REFERENCES CANSDALB, G . (1935): Reptiles of West Africa. London: Penguin Books. GUGGISBERG, c. A. w. (1972): Crocodiles. London: David & Charles.

HUNT, R. H. (1973): Breeding Morelet's crocodile Crocodylus moreletii at Atlanta Zoo. Int. Z o o Yb. 13: 103-105. MCILHBNNY, B. A. (193s): The alligator's lye history. Boston: Christopher.

(1971): Captive breeding o f crocodiles in Thailand. YANGPRAPAKOXN, U., MCNBELY, J.A . I U C N h b l s (N.S.) SUppl. 32, I : 99-100.

& CRONIN, B. W.

Manuscript submitted 16 March 1977

Breeding the West African dwarf crocodile

at Ueno Zoo, Tokyo Osteolaemus tetraspis tetraspis

KOJI HARA & FUMIKAZU KIKUCHI Aquarium, Ueno Zoological Gardens, Ueno Park, Taito-ku, Tokyo, i io lapan

In what is believed to be the first successful captive breeding of the species, Ueno Zoo in 1972 hatched and raised four Dwarf crocodiles of the West African subspecies Osteolaemus tetraspis tetraspis. It has since reared two further clutches and ten of the 13 live hatchlings are still surviving.

The parents were part of a group of four purchased from a dealer on 7 September 1965, measuring at the time a little less than I m long. One specimen died 41 days after arrival but the remaining three are still in good condition; the single 9 now measures about 1-05 m and the two $3 each about 1.4 m.

Initial diet consisted of whale and horse meat and raw scad Trachurus japonicus, but t h i s

was soon changed to live mice and rats, fed once a week. The Osteolaemus are kept on the third story of the aquarium, in a large concrete enclosure about g x g m in total area, separated by heavy wiremesh fencing into five segments. The land area comprises a circular island about 6 m in diameter with a fenced-off central plan- tation some 3 m in diameter which the crocodiles cannot enter; the surrounding concrete platform does not offer suitable nesting sites or materials. The three Dwarf crocodiles occasionally share their segment of the enclosure with some small specimens of Central American caiman Caiman n o d i l u s fusms and Estuarine crocodile Croco- dylus porosus. The depth ofthe pool is 47 cm and

BREEDING 85

the water temperature, although regulated at c. 26OC, will sometimes rise to almost 30' and fall to c. 21 "C.

EGG-LAYING

Some signs of breeding activity are usually noted every year between January and July, but since it takes place in the water, actual copulation has never been observed. In the four years that eggs have been produced - 1970,1972, 1973 and 1975 -laying has always occurred in June. This coincides with the laying season re- ported by Neil1 (1971) but differs in half a year from the December-February nesting season cited by Brazaitis (1974).

It was fortunate that all eggs were deposited in the water, for had they been laid on the concrete land surface, most would certainly have been broken. In the event, only two or three eggs were cracked when we removed them. In 197oand 1975 the eggs were discovered when keepers entered the enclosure in the morning; on the other two occasions they were removed promptly during the laying process itself. In one instance, on 13 June 1972, we were able to observe this process quite closely as laying took place in mid- afternoon, at about 1600 hours, and we could watch the actual passage of the last two of 13 eggs, with a five minute interval between. During the earlier part of the sequence an egg had been seized by one of the caimans, and as soon as she had completed the clutch the Osteolaemus 9 tried to attack; she also made attempts to bite at the net being used to remove the eggs.

On the second occasion on which the authors were present, at 2300 hours on 7 June 1973, we could see the 9 -head protruding slightly from the water, eyes closed, forelegs firm and hind limbs a little raised - but our view was obscured by the dim light and the attitude of her body. We assumed that t h i s was the laying position as three eggs could already be seen floating in the water, and in another 12 minutes nine more had appeared; seven minutes later an additional four were sighted. As the first 12 eggs were being removed, one of the 8 Osteolaemtrs entered the water and attacked the net. During this assault the 9 kept quite still, and it was not until the last four eggs were being netted that she made a move towards them; then both she and the 8 tried to strike at the net. It is possible that

while laying is in progress, the Osteolaemus 9 will not launch an attack and it is only when she has quite finished that she will move into defence of her eggs.

EGGS A N D I N C U B A T I O N

Clutch size, as shown in Table I, ranges from 10-16 eggs (mean 12.5). Published reports in thls respect are at variance: Cansdale (1955) places the upper limit at 12, while Knoepffler (1974) cites a clutch observed by Dubost of eight; and Greer (1975) in a comparison of the clutch sizes of 19 crocodilian species comes to the conclusion that, with six eggs, Osteolaemus has the smallest of all clutches. The figure quoted by Greer is the lowest for the species that the authors have encountered in their researches. But even taking account of the differences in the literature and our own experience, it seems that Osteolaemus does indeed have a smaller size clutch than any other crocodilian.

The eggs are ellipsoid in shape with a smooth surface. The mean size of 48 of the 50 eggs laid is 65.8 x 41 mm and weight 63.6 g (Table 2). When taken from the water the surface is covered with a jellied mucus which is later wiped off with a cloth. The egg is white but the yolk gives it a slightly yellowish appearance about the centre and the extremities are somewhat transparent.

One day after laying a white patch appears on the egg, which seems to act as some kind of protection for the yolk. It is at first quite narrow (13 mm when measured on the fourth clutch) and does not entirely ring the egg, but gradually it broadens and becomes annular. At the same time the slightly transparent ends are tinged first with pink and then dark red, and eventually they disappear altogether under the expanding white band. Findly the egg becomes completely milk white. Before this final change, however, it is possible to judge from the condition of the white band whether or not the egg is fertile, or whether the embryo is still alive and growing. An egg which has ceased to develop loses the distinc- tion between the white band and the rest of the surface and the tinge of red vanishes. It looks rather as it does at laying, before the initial appearance of the band.

As regards change ofweight during incubation, only one record was taken. This was in an egg weighing 65.8 g on the day after laying (8 June

86 BREEDING

DATE OF DATE OP INCUBATION PERIOD NO. OP EGGS LAYING HATCHING (days) LAID HATCHED

I1 - - 25 Jun 1970 0

13 Jun 1972 22-23 Sep 102-103 (mean 102s) I3 4

24 Jun 1975 16-18 Oct 115-117 (mean 115.7) I0 3 7 JUn 1973 3-10 Oct 119-126 (mean 123.8) 16 6

range 102-126 (mean 115.4)

Table I. Incubation and hatching of the four clutches of Osfeolaemus t. tefruspis laid at Ueno Zoo. Tokyo between 1970-1975.

LENGTH

CLUTCH (mm) WIDTH

57'0-70'5 (64.90) 56.7-690 excluding I egg devoured (60.23) 64'1-69.0 excluding I immature egg (65.30) 59'4-67'5 (63.81) 56.7-70.5

(49'7X 33'6 mm, 32'3 g)

(63.63)

Table 2. Range of egg weights and measurements; figures in parentheses represent the mean.

r973), which on 7 October weighed 63.9 g. At this juncture it had a slight crack but not sufficient for leakage ; the young crocodile emerged completely two days later.

As soon as the eggs were taken from the water they were placed into an incubator. This con- sisted of a plastic fish tank, prepared with a slightly moistened floor layer of either sphagnum moss or sand, and covered with a plastic plate. The eggs were set in the moss or buried in the sand. To prevent the medium from drying out, the eggs were occasionally sprayed around with a little water or removed while the moss or sand was remoistened. Ambient temperature in the service facility where the incubator was kept varied slightly during the three successful incubations: 23-5-33.5 "C in 1972; 22-5-32*5 "C

In the first year that eggs were laid they were all set on moss, but none hatched. In I972 an equal number (s ix) were incubated in moss and sand; one of the former and three of the latter group hatched. The following year seven (two with a crack) were incubated in moss and eight in sand,

in 1973 ; and 22'5-32'Ooc in 1975.

two of the former and four of the latter hatching. In 1975 five eggs were alloted to each medium, with two of the moss group and one of the sand group hatching. Hatching success was 33*3%, 46.1% and 37'5% respectively, excludmg immature eggs and those that were cracked at the start.

HATCHING

Incubation periods of the I 3 live hatchlings ranged from 102-126 days (mean 115.4) (see Table I).

The figures are based on the time required for the young to emerge completely from the shell. In most cases t h i s happened witlun one to two days of the appearance of the first crack, but there were three successfd eggs (all within the 1973 clutch) which took four, five and seven days respectively to hatch once they had started to crack. Three hatchlings died as they were emerging and another was found dead in the shell. Although our records in this respect are incomplete, it is esa- mated that over 80% of all eggs were fertile and that, of unhatched eggs, from one to three in each clutch contained fully developed embryos.

BREBDING 87

On one occasionin 1975 we had the opportunity of observing in minute detail one of the young- sters hatching. The crack, first seen at I727 hours, was still unchanged at 0940 on the follow- ing day. But four minutes later we noticed that the cracked portion of shell had exfoliated, and soon after we glimpsed what we later knew to be a black snout thrusting itself out; it was at once withdrawn and immediately after the head was half protruding. At 0946 hours the hatchling leaned out, exposing all but 3 cm of the head, and at 1017 it had freed itself completely. The young crocodile makes a c. 2 cm rip through the egg membrane with its egg caruncle and breaks through the shell with the tip of its snout. In almost all instances, curiously enough, it breaks one or other of the extremities, and in only one case did the egg crack through the middle.

Hatching wcights and measurements are given in Table 3 . The hatchlings were placed immedi- ately into individual plastic fish tanks, 3 0 x 1s x 20 cm, in water 1-2 cm deep. We began feeding a week after hatching, on guppies Lebistes

TOTAL SNOUT-VENT WEIGHT CLUTCH LENGTH (mm) LENGTH (mm) (g)

I972 210

217 220 210

1973 238 233 236 I99

203 I975 223

208

201

221

43'7 46.2 47's 42'7 46.0 47's 51'3 45'4 51.1 45'1 46.0 49'7 43'5

Range 199-238 105-124 43'5-51'1 Mean 216.8 IIq.0 46.6

Table 3. Weights and measurements of young at hatching.

reticulatus, loach L e f a nikkonis and newborn mice; these last, however, were the main food. The young crocodiles tended to snap at anything that was offered and were no problem to feed. Once they had grown to about 40 cm, we began replacing the baby mice with small furred ones. Feeding now takes place once a week. At time of writing (June 1976) ten of the 13 young are still alive; three of the 1973 brood have died. The four I972 young have a total length of about 80 cm, the three of 1973 are 50 cm and the three of 1975 are about 3 0 cm long.

AUTHOR'S N O T E On 27 June 1976 the 0 laid a fifth clutch, this time of 15 eggs, two of which hatched on 27 October and I November respectively. On 5 June 1977 she laid a further clutch of seven which is currently incubating. Two of the 1975 brood have since died, thus leaving, as of the present (August I977), ten of the 15 young still alive. The four 1972 youngsters now measure (total length) about 85 cm, the three 1973 young are 65 cm, the one remaining 197s young is so cm, and the two of 1976 are 33 cm long.

ACKNOWLBDGBMBNTS We wish to thank Mr M. Hisada for reading the manuscript and for his useful suggestions, Messrs H. Sugiura, Y. Yamamoto and M. Furuya for their help, and MI and Mrs Ito for translating from the Japanese.

REFERENCES BRAZAITIS, P. (1974): The identification of living crocodilians. Zoologicu, N.Y. $3: 59-101. CANSDALB, G. (1955): Reptiles .f West Africa. London: Penguin Books. GRBBR, A. B. (197s): Clutch size in crocodilians.J. Herpet.

KNOBPFFLBR, L.-P. (1974): Fauna du Gabon (amphibiens et reptiles). 11. Crocodiles, cheloniens et sauriens de l'oggoue-Ivindo et du Woleu N'tem. V i e Milieu 24

NEILL, w. T. (1971) : The lust ofthe ruling reptiles: alligators, crocodiles, and their kin. New York & London: Columbia University Press.

9: 319-322.

(C): 111-128.

Manuscript submitted 20 July 1976 (revised August 1977).