Considerations for Frog Ponds in the Tropics

As more and more people move to Far North Queensland, there is increasing pressure to remove habitat and replace it with houses. This is still one of the leading causes for frog decline in this region. It does help frogs if microhabitats can be provided for them so that they can still have places to live and breed whilst having to share that space with humans. This page covers the basics of setting up a frog pond in our tropical climate.

If you are outside Australia, please be aware that the suggested techniques and references to keeping toads out of ponds only pertains to areas where the introduced cane toad (Bufo marinus) is a pest. Australia has no naturally occuring toads so any and all attempts to exclude toads are against the cane toad. If you live in the US or Europe or Asia, you don't want to exclude your own local toad species from your ponds. In fact, many species of toads are endangered and these are species you would want to help - not exclude!

The pond itself:

• The larger in surface area the pond is, the wider variety of species that will use it for breeding. However, if all you can manage is a small pond - even one of those fiberglass kits available from the garden shops - this will still help the frogs because they need a reliable source of water during our dry season.
• It is best if the pond is at least 30cm deep and preferably 40cm or more because of evaporation and heat - especially if the pond receives more than a couple hours sun each day.
• The pond should receive shade for most of the day so that the water doesn't become too hot, but an hour or two of sunlight is needed for plant growth, tadpole development, and to warm up the water a bit.
• The pond can be dug into the ground or it can be a container sitting on top of the ground and surrounded by a decorative wall or stone, wood, tiles - whatever you like. If an above-ground pond is built and you want it to be used for breeding, the inside of one wall should have a sloping surface which will provide a shallower area for some tadpoles and a means for metamorphs to climb out.
• A small water fountain or pump will provide oxygen for tadpoles and fish in the water (as well as look lovely) but a fountain is not necessary for the frogs and should be shut off at night.
• Because of the arrival of contagious diseases which might require the draining of the pond during a certain time of year or disinfection when sick frogs have been in it, it is good if you have a ready-to-use easy system of draining the pond into the toilet or sink. This can be purpose built into the bottom of the pond when constructed or you can have a hose and pump available to direct the water into your household grey water system. If you live in an area which has experienced an outbreak of chytrid fungus or viruses, it might be advisable to drain your pond for disinfection or to drain your pond during the winter months (to control chytrid). If you are unsure whether either of these diseases has been a problem in your area, you can contact the nearest college or university with a biology program or a museum to find out. You can also check the list of verified chytrid cases from the Public Health and Tropical Medicine chytrid website.

Cane toads:

• Frog ponds are supposed to be for frogs but if you have one, the toads will happily use it. There are three ways to keep toads out of the pond: one is to make it an above-ground pond at least 50cm high with vertical walls (but some frogs don't favour these setups), and another is to dig in the pond but fence off around the pond or yard and remove the toads still inside. The disadvantage of the above-ground pond is that it will be used by the tree frogs only so the ground dwelling frogs miss out. The third (cheaper) way is not to barricade the toads out but to remove the toads and their eggs regularly.
• If you want to provide a physical barrier to toads with a dug-in pond, you merely need to provide a solid barrier which extends several inches down into the soil and reaches about 50cm above the ground. For example, a chain link or tubular pipe fence can have shade cloth attached and low shrubs or heliconias can be planted to hide the shadecloth. More information on this is in our Toad Exclusion page. If neither an above-ground pond nor a fence is possible, then a regular vigilence on the pond to remove toad eggs is the next best option. (See our pages on Toad Eggs and Humane Disposal)

Around the pond:

• There should be ample vegetation around the pond and throughout the yard. Combine plants with a variety of leaf shapes and densities so that shelter and perching spots can be used by frogs of various sizes.
• Having a source of water and shelter is only one part of the picture - another is a source of food. To encourage bugs into the yard, do not use any insecticides around the home or property, incorporate a compost pile into yard somewhere, and leave a small lamp/spotlight on in the yard for part of the night to attract moths. Planting natives which attract moth and butterfly caterpillars will also help.
• Having a lovely microhabitat for frogs isn't going to help much if predators pick off the frogs. Predators can be native species (which is a natural part of the food chain) but serious introduced predators are dogs and cats. Not only do cats attack frogs but they carry parasites which are deadly to frogs (read about this in our special threats page). If you are trying to keep out your neighbours' cats, you can add netting to the top of a fence. Smearing crushed chillies onto the fence is also supposed to have a repellant effect on cats. There may be other plants that can be planted along the perimeter of your yard to keep out other people's cats - check a companion planting gardening guide for any possibilities.
• If you have dogs or cats yourself, you can restrict their access to the area around the pond and allow the dogs run of another part of your property. Many people don't believe that dogs find frogs but they do - we see the results at the Cairns Frog Hospital. Dogs usually find the sleeping frogs during the day (we suspect they probably smell them). Cats are best kept indoors at night as frogs are not the only wildlife they prey upon. Cats hunt by instinct - not personality - so what might be a quiet, passive cat inside your home could easily become a successful hunter once let outside. One way to find out what your cat does away from home is to ask your neighbours!

Water quality issues:

• In the tropics, it is essential that mosquitoes are controlled. However, putting just any fish in the pond may completely negate the frogs' ability to breed there. Fish should be added but only use native fish which have a small mouth. Many species are suitable such as the smaller species of rainbowfish, Fly-speckled Hardyhead, Empire Gudgeon and any of the Blue-eyes. Only add two or three fish, preferably all the same sex - just enough to keep the mozzie larvae out or you'll create a food/droppings problem in the pond.
• We have started getting lab results (as of Dec 2003) of ciliated protozoa attacking tadpoles and metamorphs from some ponds where soil has washed into the pond. Please keep soil out of your pond and if you have a silt problem already, it would be best to drain the pond and clean it thoroughly and start again with fresh water.
• If you have tadpoles in the pond but not much algae or aquatic vegetation for them to eat, you will have to provide food for them or they will eat each other. Frozen lettuce (use greener varieties such as cos or butter or spinach) is a staple with a small helping of bottom dweller fish food tablets added once a week. As the tadpoles develop legs, then the fish food can be offered twice a week. Don't overfeed as the water will become fouled. If your pet shop has a product called 'algae discs', this will be easier for you and safer for the tadpoles (since commercial crops might have residues of chemicals on them).
• Also if you have tadpoles and not enough submerged, leafy vegetation, you will need to supplement their oxygen supply or they will suffocate. If you have seen tadpoles hanging vertically from the surface of the water, this is a sure sign that there is not enough oxygen in your pond. A pump or aerator running for a few hours a day should fix this problem.
• Sometimes pond owners report that everything in their pond dies suddenly (including the fish). This is often the result of a dead cane toad falling into the pond. Some native birds and rats have learned how to eat the toads without accessing their poison glands. They leave behind the head and skin at the edge of the pond and, if these body parts fall into the water, everything is poisoned. If this should happen, the entire pond needs to be drained, rinsed out and filled with fresh water which is allowed to sit for a few days before adding new fish and plants.
• Another cause of pond life dying is the use of chemicals in the yard. Avoid this around the pond and anywhere upwind/upstream of it. If chemicals should get into the pond, it will have to be drained and cleaned, as above.
• Sometimes diseases will kill tadpoles and they will die in large numbers although the fish seem fine. If this happens, the dead tadpoles should be collected right away and the Cairns Frog Hospital phoned. The tadpoles should be turned in so that they can be tested. If the tadpoles die but the fish don't, the pond might need to be drained and disinfected. Once drained, use 10% bleach to scrub all surfaces in the pond and rinse this very well two or three times. Then use 50% betadine sponged liberally over the pond liner for at least five minutes, then rinse thoroughly, disposing the rinse water in the sink or toilet. Let dry out completely for a day or so and then fill with clean water as above. The remaining live tadpoles can be dropped in to us so that we can document their symptoms and get them tested if they continue to expire. (Please note: if you are in Redlynch and have a frog pond, please read our Special Alerts page.)
• Snails should not be encouraged in ponds - they can carry the larval stage of a flatworm parasite which attacks tadpoles. If you are in the US, you should ensure that all snails are removed as soon as they are noticed and if you obtained your tadpoles from a petshop, please contact them to let them know that all snails should be removed from their tanks asap.

Frog ponds are one of the best ways to help restore frog populations in the Cairns area so we hope you'll want to put one on your property soon! Please contact us if you have any questions that haven't been covered in this page.