By Alice Pawlik, PhD student studying the links between skin microbiomes and disease in UK common frogs, lead supervisor Dr Xavier Harrison at the University of Exeter.
From their smallest (1 square m) to largest (2 ha) size, freshwater ponds can support a huge range of wildlife including insects, birds, and mammals! Across the UK, Freshwater Habitats Trust estimates that ponds are home to a whopping two-thirds of all freshwater species. Ponds used to occur in large numbers in the countryside, but hundreds of thousands, around 50%, were lost in the twentieth century. Causes of loss include neglect or agriculture-related land drainage, but fortunately, an astonishing three million ponds have been created in gardens! And these can conserve associated freshwater species by providing food, water and shelter throughout the year.
An astonishing three million ponds have been created in gardens
In addition to supporting wildlife, ponds provide wider ecosystem services by storing carbon and mitigating floods, and I feel lucky to regularly spend time at these habitats in both research and non-academic roles. For my PhD, I study amphibian disease and the microbes living on the skin of common frogs (Rana temporaria). This is a native species to the UK whose habitat now largely consists of ponds in urban or suburban areas. In my spare time, I also volunteer as trustee for Amphibian and Reptile Groups UK (ARG UK) as Amphibian officer for two of their regional groups in Devon and Cornwall, and am the current herpetological rep for the University of Exeter’s Ecological Society.
In these roles, I regularly find myself meeting people who have ponds, would like to create them, or want to know more about the flora and fauna within them. I’m often blown away by people's passion for and knowledge of their own ponds (e.g. one owner's observation that newts arrive two weeks after the full moon every February!). Additionally, I’m often asked similar questions about pond creation, management and associated creatures. In the Southwest of England where I’m based, amphibians start breeding very early in the year, as early as November at some locations! Now that the ponds nearby are full of spawn, and ponds around the country are following this trend, I thought it timely to write this Q&A.
We have seven native amphibians in the UK, and in the following blog I answer questions about pond creation and management, and the amphibians that often occur in garden ponds. For spawn, I am referring to common frogs and common toads (Bufo bufo), and when mentioning newts I’m referring to our three native newts; the palmate newt (Lissotriton helveticus), the smooth newt (Lissotriton vulgaris) and the great crested newt (Triturus cristatus), though the likelihood of each occurring in a garden depends on geographic location (see image 1 for pictures of each species). I am answering in my own words, not on behalf of the organisations I work with, and also provide links to resources for those keen to learn more!
Image 1: UK pond amphibians (Images: frog by John Baker, toad by Steve Langham, newts author's own).
1. I’ve found spawn (frog) in a drying puddle/my friend has a lot of spawn, can I move it to my pond?
Opinions differ on this, but I always advise against moving spawn due to the pathogens and invasive plant species that can be present on spawn, but not visible. For example, the Chytrid fungus (Batrachochytrium dendrobatidis) and ranaviruses have decimated amphibian populations around the world, and both are present in wild amphibians in parts of the UK. However, these pathogens often cannot be detected (without molecular techniques) until you see dead or dying amphibians. We also have various other pathogens, parasites, and invasive animals impacting our native amphibians, so I tend to think of it this way; amphibians do migrate between their terrestrial habitats to a pond in the breeding season, but humans have the ability to move spawn over much greater distances than amphibians can travel on foot. In doing so, humans are risking the movement of disease and invasive plants to locations they might never naturally reach.
There’s also no need to take spawn home, or into classrooms, to watch it grow. The chance of the spawn not developing here can be high, and you can watch development by simply revisiting the spawn in the wild or in your own pond instead (the Gosner staging chart is a great way to follow development stages). Amphibians also have habitat preferences, and if they have laid spawn in a shallow pool, but not in your garden, there might well be a reason why. For your own pond, frogs may not have reached your area on foot yet, or your pond may not be suitable (more on the latter in question 2). In general, common frogs prefer to lay in shallow water so that these egg masses warm and young are encouraged to feed, grow and metamorphose, and receding water levels can even spur on this growth.
As common frog adults do not tend to their young, they themselves will not know whether their spawn has survived or not, or maybe even to avoid a pond that regularly dries. This style of breeding is why many amphibians lay many eggs at once, rather than spending similar energy caring for a small amount of young. Finding spawn in low water levels can understandably cause distress for those who worry about the spawn or hatching tadpoles dying, but a drying pool may not spell disaster for all the eggs in each spawn clump. Developing tadpoles might survive within the safety of the moist surrounding spawn due to varying developmental rates. Each spawn clump also represents one female frog, so the loss of one clump laid in a very shallow spot does not mean the loss of an entire frog population in a geographical area.
When finding spawn in dried pools (see Image 2), I often check the weather forecast for upcoming rain to calm any nerves about drying! However, if things are critical, for example; the pond is nearly dry, the water is being polluted, and there is a suitable waterbody incredibly close by (say within 100 feet) where the spawn could naturally occur, human intervention could mimic natural amphibian movement, and would fall within any associated disease spread range.
Image 2: Spawn in a nearly dry pond, Cornwall (Image: author's own). It’s been a dry start to the year here, but fingers crossed the moisture remaining around/in/under this frogspawn will allow the tadpoles to develop as it’s looking like a healthy bunch.
2. I would like amphibians in my pond, why are they not here yet?
This is a very regular question and can be answered with this concept; build it and they will come, and if they don’t they may require more time, or something might need adjusting. For the latter, there are some main questions to ask to help explain why amphibians might not have reached your pond yet, or might not currently find it suitable, and how you can encourage them in:
Does your pond have multiple “microhabitats”?
The insects, birds, small mammals, plants, and amphibians that dwell in ponds each have habitat preferences, and it can be difficult to create or maintain a pond which is suitable for all. However, where possible, including multiple “microhabitats” such as a shallow-sloping pebbled beach area, an area of deeper water, and letting vegetation grow in and around pond edges can help to cater for many species. Frogs, newts and small birds will enjoy the shallow areas, a sloping beach will allow amphibians and small mammals to enter and leave the water safely, and deep areas will be suitable for toads. Areas of vegetation will help invertebrates such as dragonflies to land and emerge, provide egg-laying sites for amphibians, and can shelter all from predators. Creating terrestrial garden features such as refuge sites known as “refugia” and areas of tall vegetation can also provide shelter and foraging sites for amphibians and other wildlife (see resources at end of the blog for habitat creation ideas).
Is your pond/garden accessible?
Amphibians spend time on land and water, and often travel a good distance to reach breeding ponds in the spring from terrestrial refuge areas such as woodlands or rockeries. For example, frogs and newts are thought to cover up to five hundred metres, whereas toads can traverse a few kilometres to reach their ponds! Toads in particular return to their ancestral ponds every year, no matter how dangerous the journey is (to help them reach these ponds safely, see Toads on Roads project). Raised ponds also benefit from stone steps or heaped soil to aid wildlife entering and leaving the pond, but the surrounding area must also be accessible. For example, ponds in built-up areas may be inaccessible to amphibians unable to cross roads, train tracks, or get past wooden fences. And these barriers can change each year, e.g. with new development. Ponds in built-up areas may simply be inaccessible for amphibians or mammals but can still be invaluable for plant and insect life! If amphibians are near, then cutting holes in the bottom of your fence or leaving good-sized gaps under gates can allow ponds and terrestrial refuge “islands” in urban or suburban areas to be linked up and encourage them into your garden.
Do you have fish or ducks in your pond?
Native frogs and newts tend to shy away from fish ponds as the fish can reduce their prey and eat their young. Ducks and fish can also cause changes in pond water turbidity by stirring up sediment to eat and through defecation, this can influence the ability of plants to grow which can in turn impact water quality and the available shelter for amphibians and their invertebrate prey. Some amphibians, such as newts, also wrap their eggs in plant leaves, and so reduced plants mean a lack of laying materials (newt egg information/images available here). However, ponds with fish can still be suitable for common toads, as this species coats its spawn in a toxin that deters predation. Toads do tend to prefer deeper ponds where they can wrap their spawn around sunken vegetation, so if you’d like amphibians and fish, deep ponds are best. Netting a pond, with space underneath for amphibians, small mammals, and small birds to enter and escape, can help to discourage larger feathered friends such as ducks and herons.
If space, time, and funds allow, making smaller wildlife ponds alongside larger fish or wildfowl ponds can help to increase the overall pond biodiversity in your garden or greenspace (see resources at the end for guidance). And don’t lose hope! It can simply take time for amphibians to find your pond. In my experience, amphibians can also occur in the most unlikely of places, and some ponds buck the aforementioned trends completely (see Image 3). For example, whilst surveying ponds in Devon for my PhD I found common toads, common frogs, and palmate newts, all living alongside Koi fish in a large, deep pond! I believe the pond’s deep main basin, coupled with a shallow shelf around its edge allowed the species to co-exist.
Image 3: A multi-species pond in Cornwall (Image: authors own). Common frog spawn (left of image), common toads (top middle), toad spawn (top right, wrapped around vegetation), and a male palmate newt (bottom middle), all occurring at the same time in one pond located in Cornwall. Image captured during frog surveys in 2022 for my PhD
3. Why has the frog spawn in my pond become discoloured/sunk/not developed?
For common frogs, when spawn is first laid, it is formed of small eggs tightly packed together (spot the very fresh clump of spawn directly above the leaf near the top of Image 2). As it absorbs water the eggs swell and the spawn can sink below the water surface. The best place for spawn to develop is in warm areas, so sinking just below the surface isn't bad, but at greater depths it may develop more slowly. This is why it's best to have shallow areas in your pond or to allow vegetation to grow to cradle the spawn and keep it warm. For common toads, toad spawn is laid in long strings around vegetation, and can often be found below the surface or at the bottom of the pond, this is normal and nothing to worry about.
Discoloration, on the other hand, can be due to many things, if the spawn is laid in a sediment or algae rich pond then it may simply be coated in this. You can also tell if spawn is relatively healthy by looking at the dark dot in the centre of each jelly egg, the embryo. This should be dark brown or black, and if they have turned white or grey the eggs are likely dead, or in a very rare event these could lead to albino amphibians. You might also see no embryos at all, this is likely unfertilised spawn that a female has laid. When this is found on land it is often called “star jelly” and can be a sign of amphibian predation. If spawn appears to be white, cloudy, and fluffy in appearance then this can be a sign of the naturally occurring Saprolegnia fungus which can infect both dead and live spawn. If you see signs of the latter, it’s best to report it to Garden Wildlife Health so they can monitor its occurrence.
Additionally, spawn may not develop due to changes in environmental conditions. For example, high temperatures, changes in pH, over shading, ultraviolet-B radiation, or pollutants entering the water can all cause spawn to die. Leaving ponds to mature naturally, allowing vegetation to grow around them, and not using garden management chemicals near them can reduce the chances of drastic water chemistry changes, or pollutants entering the waterbody.
4. I used to have newts/frogs/toads in my pond, why don’t I this year?
Amphibian populations will naturally fluctuate from year to year, and it takes time for young amphibians to mature and return to ponds to breed. So, if you have a quiet year, this may be due to natural age range differences including young amphibians not being back at the pond yet, or losses of older amphibians from the population. Frogs and toads also tend to return to the same pond every year, but if a new pond is found on route by young adults breeding for the first time, this could become their new breeding site. Amphibian species numbers may also change due to predation and competition. For example, if a heron, or domestic animal has taken a fancy to your pond's amphibians, numbers may drop.
The differences in pond inhabitants might also be due to a change in species suitability, e.g. if the pond is now shallow due to vegetation succession it might now be preferred by frogs. The rate of amphibian predation or species diversity might also change year on year and have impacts years later. For example, other amphibians and invertebrates may have made it to the pond at the same time as spawn or newt eggs were being laid a few years previously, this might have reduced the number of juveniles recruited to the population that year, and combined with general population fluctuation (e.g. death from predation or road accidents), you may see the knock-on effects of this when fewer, now mature, amphibians make it to your pond this year. Furthermore, if a new road has been built in your area, the amphibians may struggle to reach your garden. If you have space, building terrestrial refugia and hibernation sites (hibernacula), such as log piles, tall grass, and wildflower patches can attract invertebrates into your garden and encourage amphibians to stay closer to your pond year-round by providing shelter and food near to the pond (habitat creation resources at end of blog).
5. I don’t have a pond! Why do frogs/toads keep coming to my garden?
Frogs and toads often return to the same pond year on year, even if the pond is removed, or dried up (a la Image 1). And may spawn even if there is no water for them to lay it in. If they keep turning up in your garden in the spring months, it may be time to build a pond! A new pond can be created at any time of year, but if you can’t install a full one right away, or a permanent one at all, consider popping out a paddling pool or washing up bowl with rainwater and access and exit points to help the desperate adult amphibians (see pond creation resources at end of blog).
6. My pond has frozen, what should I do?
With changing rainfall and temperature levels in recent years, amphibians now often begin breeding in ponds before the last frosts of winter. Freezing temperatures can cause frost damage to parts of frogspawn directly exposed to it and kill these developing eggs, but might not spell disaster for the rest of the submerged spawn clump/s. You can clear snow from the top of iced over ponds to allow light to penetrate the water for plant growth, but adult and young amphibians can survive below the ice. Amphibians often overwinter in ponds, and low temperatures mean that less oxygen is being used by resulting slow-moving animals. So sudden drops in temperature during a breeding season do not mean that your pond inhabitants immediately need oxygen (see Image 4). If you are worried, add a ball to the water surface before frosts so that this can be removed to open up an air hole during periods of ice cover without breaking the whole ice sheet, as this can stress animals beneath the surface.
Image 4: Action under the ice! Common frogs in amplexus, the breeding position of frogs and toads, under an ice-covered pond in early 2023 (Image: Dr Silviu Petrovan).
Thank you for reading this pond Q&A! Hopefully the answers will help you encourage amphibians into your pond, or inspire you to create a pond in your garden or green space! Please use the resources below for more information about pond or terrestrial habitat creation, amphibian disease, how to report your amphibian observation, and how to get involved in amphibian conservation! And if you have further questions, please contact your local ARG group, or me at ap853@exeter.ac.uk.
To find out about your local amphibian and reptile group, visit: www.arguk.org/get-involved/local-groups
For (free) amphibian identification information go to: www.arguk.org/info-advice/id-guides
To record sightings of amphibians and reptiles, visit ARG UK and Amphibian and Reptile Conservation Trust’s amphibian and reptile recording site: www.recordpool.org.uk/
Add your observations of spawn to Freshwater Habitats Trust’s 2023 spawn survey here: freshwaterhabitats.org.uk/projects/pondnet/pondnet-spawn-survey-2023/
To learn more about the diseases afflicting amphibians in the UK, including Chytridiomycosis and ranavirus, visit: www.gardenwildlifehealth.org/garden-wildlife
To report dead or dying amphibians/other wildlife, visit: www.gardenwildlifehealth.org/
Additionally, you can watch the video I created on this as part of my PhD: https://youtu.be/MUygyi6Jt0k
The Be Plant Wise campaign: www.nonnativespecies.org/what-can-i-do/be-plant-wise/
And finally, for aquatic and terrestrial amphibian habitat creation/maintenance, I suggest Amphibian and Reptile Conservation Trust’s Habitat Management Handbooks (online PDF’s), an online help guide like this one by RSPB, or a pond creation book such as “The Wildlife Pond Book: Create Your Own Pond Paradise for Wildlife”, by Jules Howard.