B R E E D I N G

Breeding and rearing the Colombian giant toad

at Krefeld Zoo

Bdo blortilergi

PAUL VOGT Asistarit Diructor, Krefelder Zoo, $15 Krefeld, Gertriariy

Krefeld Zoo had four Colombian giant toads Bufo blortilcrgi in its collection; one ? had been there six months, two J$ and one a fortnight. The sexes were clearly distinguishable : the 93 measured 20 and 21 cni and weighed 600 and 700 g respectively; the 63 15 and 17 cni (weights 3 5 0 and 500 8). In the 66 the upper side of the thumb was a dull dark brown, in the ?? pale brown like the rest of the hand. The 33 usually croaked after evening twilight and this enticed the 99 into the tank. When the 6$ were seized in the nape region they reacted by croaking and by making more strenuous defensive move- ments than the PO.

The more recently received 9 spawned on 2 April 1972. The two $3 clasped her on the back and belly respectively. When releasing the eggs the 9 held her back in a concave position, with hind linibs half outstretched, wlde the $8 massaged her cloaca1 region with their hindlimbs as they shed their sperm. At 0800 half the spawn had appeared, by 1400 the two chains were complete, each measuring 10 in. Shortly before this the $6 had released their embrace. In the first portion spawned, the eggs were loose in the jelly but in the remainder, the eggs were so closely packed that they were transformed into polyhedral structures. The total number of eggs was about 80,000.

D E V E L O P M E N T IN T H E W A T E R

The nornially formed section of spawn was divided up between several shallow tanks, and draped over water plants. Chlorine-free water had been previously inoculated with plankton froin a pond. The water temperature was kept between 22' and 25Oc with the help of the thermo- stat, while aeration provided an oxygen supply and water movement. Two-thirds of the water volume was replaced each day, using water that had been allowed to stand.

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Development proceeded as follows. On the day after spawning, gastrulation was complete. On the third day the embryos were 3 mm long, the eye rudiments were recognisable and the protective jelly had loosened. At first they clung to the jelly by means of their attachment organ, but then they fell to the bottom. On Day 4 the embryos showed slow lateral flexions, and on Day 5 the first swimming movements were visible, but they did not move away. External gills appeared on about Days 5-6. By Day 7 the tadpoles had a total length of 12 mm (head and body 5 nun) and feeding movements and de- faecation were first observed.

Froin Day 9 onwards they were given a suspension of twice-cooked nettle powder once or twice daily, which formed a thin film that could be easily 'grazed'. The tadpoles received a protein supplement in the form of a tabloid fisl- rearing preparation. There were originally about I 500 tadpoles but by metamorphosis the number had reduced to 1200, probably because their density was too great in the tanks. Some of the tadpoles stopped feeding and swam round con- tinuously, becoming more and more emaciated. Norinally the resting tadpoles clung to or beneath objects. During feeding they showed negative phototactile behaviour when disturbed by vibrations or a sudden shadow.

M E T A M O R P H O S I S

The first signs of approaching metamorphosis appeared on Day 26. They stopped feeding and lay close to the aerator or on flat surfaces half out of the water. The hindlimbs, previously held loosely backwards, began to be extended wlieii swimming and flexed when resting. The average length of the tadpoles was 27 mm, of which the head and body accounted for 10 nim; the greatest breadth, at the junction between head and body, was 6 mm. On Day 30 some of the tadpoles had

88 B R E E D I N G

free forelimbs and the resorption of the tail began. The previously uniform brownish-black pigment became broken up by shiny brownish dots, which provided an effective protective colouration when seen against the sandy substrate. On Day 33 the first little toads were seen teniporarily on land, and permanently so on Day 34. As the number of land-living toads increased the water in the rearing tanks was reduced in area by increasing the amount of sand. Six to seven weeks after the spawning all the young had metamorphosed. Slow-growing tadpoles produced smaller toads or died. An almost albino tadpole died at 60 days, without showing any sign of metamor- phosis.

D E V E L O P M E N T O N L A N D

During the first month the sand was kept damp, with small areas of water for the little toads to bathe in. As they frequently urinated and de- faecated in the water, I provided small shallow water dishes (depth 10 mm, because of danger of drowning), so that the water could be renewed. The vivaria were sprayed with water in the morning and evening, so that air humidity and the wemess of the substrate

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fluctuated regularly. The average air tenipera- ture was 25'c, with a range of 2oo-3o0c.

I observed the first little toad feeding on Day 2. For four weeks I fed them on aphids. The size and speed of movement of this type of prey were most suited to the capabilities of the toads. Even stumpy-winged fruitflies Drosophila melano- gaster were too large and too fast. The vivaria were only sparsely planted so that the prey could be easily seen and even followed for a distance. For the same reason the pieces of bark serving as shelter were removed before feeding. Spraying with lukewarm water increased their eagerness to hunt for food and at the same time stimulated urination. After a month the diet consisted of fruitflies and small flies from manure heaps. As the young toads became increasingly active at twilight, 1 helped them to capture prey by placing a light (outside the vivarium) so as to keep the flies within shooting distance of their tongues. From the fifth month they were mainly fed on bluebottle larvae and migratory locust hoppers. After eight months the largest of the young toads were capable of taking young mice.

During their first weeks the young toads showed positive phototactile behaviour when

2 3 L 5 6 7 8 0 1 o l 1 1 2 age in months

Fig. I. metamorphosis.

Growth rate of a Colombian giant toad Bufo blombrrgi reared at Krefeld Zoo. Arrow indicates

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disturbed, but later this became negative. During the day they seldoni left their dark hiding-places, where there were often several packed close together. They are active at night and regularly went into the water for 10-1s minutes in order to make up any loss of water. They would then also urinate, but defaecation took place on land.

Their growth is shown in Fig. I. During the first year the increase in body length and weight was almost linear. The transition from the irregular spotting of the young to the pattern of the adults - a greater contrast between the pale upperside and dark flanks (Fig. 3e) - was complete by the sixth month, at a body length of about 35 nim. The frequent moultings during growth took placc on land. The toads hold the head down and bcnd thc back so that it becomes convex. The old skin splits straight along the midline of the back and is puslied off with the hindlimbs altcrnatcly as far forward as the

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parotoid glands. This is helped by inflation of the belly and downward movements of the lower jaw. The old skin pushed off with the forelimbs remains hanging from the underside and is rubbed off in the water. The new skin is at first paler and shiny.

Fig. z illustrates the survival rate of the young toads. A large part of the initial losses must have been due to competition for food. The loss of all the animals in one vivarium ( 3 5 0 ) and of a large proportion ( m 150) in another vivarium about ten weeks after metamorphosis cannot be explained. Although given the same diet as the surviving animals and although in good nutritional condition they died showing paralysis (first the fore- and then the hindlimbs) and convulsions. Most of the later cases of death occurred under similar conditions, and in old animals there was also copious secre- tion from the parotoid glands. It is possible that overcrowding caused auto-intoxication.

Fig. 2. Proportion of BU$J blombvrgi originally hatched at Krefeld Zoo surviving the first year. Arrow indicates metamorphosis.

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Fig. 3- Stages in the development of Bufo blombeqi. a. IZ days, b. 25 days, c. 30 days, d. 4 months, e. 6 months.

The fast-growing individuals developed nor- mally without a vitamin supplement. From the eighth month the smaller individuals showed rachitic malformation of the hindlimbs, which

could be improved by giving a multi-vitamin preparation.

Manuscript submitted 26 March 1973

Breeding the Harpy eagle Harpia harpyja

at the Los Angeles Zoo FRANK S . TODD' & TOM MEACHAN2

'Corporate Curator ofBirds, Sea World, Sun Diego, CaliJbrnin gzrog, arid aKeeper, Los Aizgeles Zoo , Ca\$mia 90027, USA

Although birds of prey have been kept in captivity for hundreds of years, accounts of their breeding are comparatively rare, and it is only in the past decade that some of the more common species have begun to reproduce regularly. The failure to breed is usually the combined result of improper facilities and lack of patience. Indeed, many aviary designs make nesting impos- sible, while the majority of zoos are not willing to make the long-term commitment required to

carry out a captive raptor breeding programme. Patience and planning are vital because, with

birds of prey, all phases of the nesting process, from nest building to care of the young, have to be learned. Each successive nesting attempt should progress a stage further than the previous one until success is ultimately achieved. Evcn in the wild, the learning process is a long one, often with the first nesting attempt ending in failure. It is unlikely that two first-year breeding birds

lFrank Todd was formerly Curator of Birds a t the Los Angelcs Zoo.