SPACE HOPPERS

Captive breeding the starry night reed frogs

by Tim Baker, LVI Lead Keeper at Drayton Manor

The starry night reed frog (Heterixalus alboguttatus) is one of the larger species of Heterixalus with females growing up to around 40mm SVL and males a little smaller at 30mm SVL. They are quite variable in background colour from pale yellow/ white through to blueish hues or dark purple-black. Variation seems somewhat dependent on temperature, light levels and time of day. Throughout these variable colours, they retain the yellow and black dorsal speckles. The ventral colouration is white/cream and the feet and lower limbs are orange. They occur in the East and South-East of Madagascar in low-mid elevation savannah, grasslands, degraded habitat and agricultural areas. They can be found sunning themselves in the day on exposed leaves, and at night they use a multitude of perching to hunt and locomote in their environment. This species breeds in small water bodies such as ponds and paddy fields. Considering their body size, they are capable of laying a surprisingly large number of eggs amongst sunken twigs and leaves, the details of which I’ll revisit later.

At Drayton Manor Zoo over the past 6 years, we have been working towards diversifying our herpetofauna collection which now stands at 64 species, of which 23 species are Madagascan. We chose the Starry night reed frog at Drayton Manor Zoo to increase species diversity in one of our otherwise conservation-focussed Madagascan-themed exhibits, holding critically endangered Golden Mantella (Mantella aurantiaca) and endangered Yellow-headed day gecko (Phelsuma klemmeri). It has so far worked out well, providing a diverse mixed exhibit that works for the species housed and for the interested viewing public.

Creating the perfect reed frog setup

The Starry night reed frogs at Drayton Manor are housed with Golden Mantella (Mantella aurantiaca) and Yellow-headed day geckos (Phelsuma klemmeri). Since the exhibit was created over a year ago, there have been no apparent issues with this set-up. The exhibit is around 150cm3 with numerous microhabitats provided by Madagascan ferns and reeds. Complex rockwork and bamboo provide lots of crevices for refugia and egg-laying sites, and a deep substrate with lots of leaf litter helps regulate relative humidity within the exhibit. The substrate provides the frogs with an option to burrow away during the drier seasons too. Creating a successful mixed exhibit can come with its challenges and we are very careful in the decision-making process to avoid any potential issues such as predation or resource dominancy. Where we can, we like to create mixed exhibits that are accurate to the geographic region for the flora and fauna in them, so in this example, we have Malagasy flora and fauna mixed in a way that suits all the inhabitants but also is a great way of creating an informative biotope for guests when they visit. It allows them to learn about not only each species, but their natural history, ecology and relationships they share with other species from the natural habitat.

We have a mixture of plants in the exhibit, and we have tried choosing Madagascan plants where possible, to ensure they are relevant to the ecology and habitat of the species present. We have a fast-growing Madagascan sedge plant that the reed frogs like to rest on in the day, as well as some broader leaved plants like Madagascan stags horn ferns that act as daytime refugia and basking areas. There is lots of moss and low-lying ferns growing on the ground, which provides lay sites for the Mantella. The dead bamboo is what the Phelsuma klemmeri live on in the wild, and apparently are never found on the live bamboo so this was a consideration here too.

When we create mixed exhibits, we must ensure the presence of one species is not going to negatively impact another to make it successful. So, in doing this, we consider; useable space- is there enough space for all individuals to live, thermoregulate, feed, and locomote separately and all together? There needs to be a consideration for multiple, suitable, relevant microhabitat provisions for each species/individual and preferably each species within the enclosure occupies a separate niche to minimise resource competition/dominancy. Is there a size difference between species? Is there a predation risk? Are the climatic conditions suitable and relevant to all inhabitants, and not that conditions are optimum for one and ‘acceptable’ for another? We also consider the geographic accuracy of mixing species to make it informative for guests but also generally means if you are mixing sympatric species or species from similar habitats, in most cases, they require very similar climatic conditions and occupy different niches. Some of the other Malagasy mixed species exhibits we have done at Drayton include leaf-tailed geckos (Uroplatus henkeli) with tomato frogs (Dyscophus guineti), radiated tortoises (Astrochelys radiata) with spiny-tailed iguanas (Oplurus cyclurus), day geckos (Phelsuma kochi) with giant water skinks (Amphiglossus reticulatus), and ground geckos (Paroedura pictus) with three-eyed iguanas (Chalarodon madagascariensis) and girdled lizards (Tracheloptychus petersii), to name a few.

Environmental conditions

Reed frogs, geckos and Mantella all occupy different niches within the exhibit and therefore rarely interact with one another (aside from the odd time a reed frog bounces down in front of a Mantella to take the food it was about to eat…but providing enough food is provided, this has never been an issue over time). The geckos usually occupy pieces of dead bamboo, higher up in the enclosure, as they would in the wild. They live amongst the cracks and crevices within the bamboo and this is where the eggs are laid, basking sites are found, and where the refugia are. The gecko eggs have so far, been incubated in situ. The Mantella live and breed amongst the leaf litter and moss within the enclosure at ground level. The reed frogs utilise the whole enclosure but are most active at night. During the day they are resting and therefore rarely interfere with other cohabitants. At night they are awake, moving around the enclosure hunting. They are small enough to not pose a risk to the other species in the enclosure and seem to live alongside them without incident. There is also a densely planted pond at the rear, that allows the frogs to swim and hydrate, and also probably helps to maintain ambient humidity levels. Temperatures and relative humidity during the day and night vary throughout the year to replicate what occurs in the wild habitat in Madagascar. There is a drier, cooler season followed by a warmer wetter season which aids breeding stimulation. In summer, it can get to 30-35C in the upper levels of the exhibit and 25-27C in the lower areas, whereas in the cooler season it may drop to 12-17C in the lower areas and 20-30C in the higher areas. Humidity is always higher at night than during the day, as it would be naturally in the wild and this aids passive hydration. In the drier seasons, it can drop to 40-50% during the day and in the wetter seasons, it's usually 70-80% during the day. The Heterixalus appear to need this prolonged dry period to generate eggs, as with regular spraying/higher humidity, they tend not to generate eggs in my experience.

Stars in their eyes

Back when we initially acquired this species, we got 2.2 young adults (two males and two females). The enclosure was a simply designed Exo-terra glass terrarium measuring 45x45x60cm, with no substrate, potted plants and thin branches for perching. This design allowed us to maintain good hygiene levels and also the opportunity to periodically flood the base of the tank in future. We kept them like this off exhibit for an isolation period in line with our in-house biosecurity measures during which time they were kept quite dry, and I noticed the females were getting particularly ‘full’ with eggs, becoming visibly rotund. You could see the eggs through the skin laterally in front of the hindlimbs. At this point, they were out of isolation and I set up a simple closed-system rain chamber with a small pond pump, some piping and a spray bar mounted below the roof mesh and flooded the tank base. I mounted the spray bar to rain on around 50% of the furnishings and left the rain on constantly. By doing this, the frogs had a choice to avoid the rain and dry off if neededthis is something to consider because I have since noticed they are quite prone to bacterial skin issues if they are constantly wet in rain chambers for prolonged periods. Although we never observed any calling or amplexus, by the third morning of rain, the frogs had spawned. Based on the quantity of spawn, we assumed both females had spawned- until we found one female still very big and hadn’t spawned. We had 11 separate clumps of eggs sunken below water level, anchored to sunken twigs, leaves, and other décor. Each clump had around 20-30 eggs and we experienced an estimated >95% fertility rate. Eggs were mostly uniform black colour, and some were 50:50 white:black. Some of the white:black eggs developed, but some were infertile. All the black eggs developed. Development in this species is fast! Eggs hatch within 5-10 days and the tadpoles consume the remaining infertile egg and jelly mass. This immediate consumption of infertile eggs makes it difficult to calculate exactly how many were infertile, but in total, we hatched over 300 tadpoles. We set up water tanks with a temperature of around 20C but after some initial losses, we increased the temperature to 24C. We took a little bit of time experimenting with what the tadpoles enjoyed feeding on, and through this, we had some

Space Hoppers

husbandry. After around 6 months, the froglets were of a subadult size and some of the frogs we bred are now on exhibit with the rest of the adults. In total, we morphed around 200 froglets and they all survived to adulthood. We now have a nice group of 23 adults on exhibit, of mixed sexes and bloodlines, and the rest were moved to other zoological institutions in the UK. This species is rarely bred in both zoos and private collections, so it’s been really good to expand the holding in captivity.

Wild research

I travelled to Madagascar in 2017 and saw this species in Ranomafana village, which for any keen wildlife nerd, is awesome. The Heterixalus were found breeding in a reed-filled garden pond, with 4 - 5 other frog species. We also saw them on nearby fence railings, and in some dense riparian habitat that was just teeming with different species of frogs of different sizes, colours and ages. I took some temperature and UVI readings in the habitat, as well as habitat photographs to inform any future husbandry for various Malagasy species throughout the trip. All this data has been used to inform the husbandry decisions we have made at Drayton, alongside other published references and online data.

Advice for private keeepers

cannibalism of tadpoles by other, stronger tadpoles. We believe this should be avoidable in future with the correct food items available from hatching. In the end, they fed well on cucumber, natural algae growth in the tank, fish flake, spirulina, tree bark and magnolia leaves. Water parameters (NO2: 0, NO3: 0-50, GH: 14, KH: 6-10, pH 6.8-7.2, Cl:0) were maintained by regular daily water changes and waste removal, as well as feeding little and often up to 5x daily. The tadpoles were raised together in a 60L tub that was heated by fish tank heaters and maintained at 24C with a few degrees drop at night. Under these conditions, development was fast, the tadpole stage took around 70 days.

We were surprised at how much food the tadpoles ate, the appetite was seemingly insatiable. In comparison, a similar quantity of Red-eyed tree frog (Agalychis callidryas) tadpoles may consume 50-75% less food than the Heterixalus within a set time. It is impressive how many eggs come out of such a tiny frog species. The females are so swollen before spawning that they look more like tomato frogs than tree frogs.

Once the tadpoles had popped all four legs, they were removed from the main tank into smaller shallow dishes to morph out into small containment tanks. The containment tanks had damp paper towels and moss to aid in hydration retention. Once the froglets had absorbed all their tails, they were transferred into planted 45cm3 glass terraria with soil, leaf litter and moss. The froglets had large appetites just like the tadpoles and fed well on pinhead crickets and fruit flies within 24hrs of the tail being absorbed. I have heard of smaller metamorphs having to be started on springtails, but we did not have this issue and the variation may be due to differing tadpole

Starry night reed frogs can be described a bit like Flubber - they bounce from wall to wall with tireless energy and are very good runners too. This means the keeper must have their wits about them when entering the enclosure to avoid escapes. They also seem to benefit from a choice of microclimate. This way, they can choose to sit and bask in the open air on top of a leaf or other solid surface, but equally can reside in crevices or under leaf litter. Keepers must be extremely vigilant on the cleanliness of the tank, as bacterial issues can affect the frogs, especially in periods of higher humidity. I’d always recommend live plants over plastic. They are less of a harbour for bacteria and help maintain humid microclimates within the enclosure. Also, a nicely planted tank is very aesthetically pleasing but it does have to be functional for the animal before being pleasing for the keeper. We keep 25 in a large enclosure, but I’d say the highest density without affecting welfare and hygiene would be 10-15 adults in a well-planted 60x45x60cm glass terrarium. They certainly benefit from UVB exposure too. At Drayton Manor, we keep ours within 0-3UVI and this provision will also help the frogs stay on top of dermal bacterial issues.

About the Author

Tim Baker is the Lead Lower Vertebrates and Invertebrates (LVI) Keeper at Drayton Manor Zoo. He has been keeping reptiles and amphibians since 2013. He works closely with species from Madagascar, Pantanal, southern Africa and the deserts of southwestern USA to maintain a diverse collection of species with a conservation interest.