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Frogs and toads are a frequent visitor to UK garden ponds. If you are lucky enough to have a pond of your own, you may have noticed that it is full of spawn come the springtime, but when do the amphibians arrive, and where have they been during the cold winter months? Here’s a look at what they do and where they go.
The frog, and all amphibians such as toads and newts, are ectothermic. This means that they are cold blooded animals that have no ability to generate internal body heat and rely on external heat sources such as the sunlight to maintain their body temperature.
Therefore to avoid freezing to death during the winter, they need to hibernate in a sheltered place that protects them from the most extreme temperatures. They will begin to hibernate during November, typically emerging some time in February. During this time, their metabolism slows down and they are largely inactive.
Frogs have permeable skin, which means that they need moisture to cross the skin barrier in order to avoid drying out. This means that they will seek out a damp environment to spend the winter, usually on land. They may burrow into a compost heap or find an old animal burrow, or even soft soil.
Other usual places that amphibians tend to hibernate are among fallen piles of leaves and other debris, so leave a corner of your garden deliberately untidy during autumn and winter to allow for this, especially if you have a pond. They will also overwinter under logs or within the small crevices in piles of logs.
However, adult males may occasionally bury themselves in the mud and leaves at the bottom of a pond. The danger of this is that if the pond freezes over completely, the frog might become starved of oxygen and die. Should they survive, they are well placed for being the first to mate when the females arrive in the spring.
If you have a garden pond, prepare it for winter by removing excess leaves, because these can leach toxic chemicals and gases into the water. If the pond is covered by a layer of ice for a number of days, these can build up and cause frogs and other wildlife to die. Clear the snow off the surface of a frozen pond to allow the sunlight to reach the plants.
You can give frogs and other wildlife the best chance of survival during the winter by making sure that your pond is well stocked with oxygenating plants.
Willow moss is a particularly useful species to stock up on for the winter months because it is hardy and can cope well with cold temperatures. It is a dense-growing plant with feathery green leaves that provides good cover for newts and tadpoles, so come springtime it will help to support the breeding season.
Leave a light object such as a rubber ball floating on the surface of a pond in winter to prevent the entire surface from freezing over. Should the pond completely freeze, do not attempt to defrost it with hot water, chemicals, salt, or by smashing it with a hammer, as this can cause serious damage to the wildlife or structure of the pond.
Remember that frogs are very hardy and have evolved to cope with freezing winter conditions, and most of the time they will manage very well without interference. Sometimes amphibians will die during the winter because they have simply reached the natural end of their lifespan, rather than because they have perished in harsh conditions.
Some species of frog that are not native to the UK such as the wood frog, have adapted to the extreme cold climate of Alaska and the Arctic Circle by producing a special antifreeze substance in their bodies. This prevents ice from freezing in their cells, although it does freeze between the cells, so the frog is effectively in a semi-frozen state.
When the weather warms up in the springtime, the wood frog will defrost and be ready to begin the mating season.
During milder winter spells in the UK, you may notice that amphibians will have periods of brief activity before re-hibernating. Newts will sometimes not hibernate at all in a mild winter, but maintain a low level of activity.
You can help amphibians to overwinter in your garden by following the previously mentioned steps of making sure you have oxygenating plants in your pond, and by clearing off lying snow and creating a hole in the ice with a floating rubber ball during cold snaps.
Furthermore, deliberately leaving some piles of leaves and other garden debris will provide amphibians with places to hibernate. They will also seek out rockeries, so consider building one if you have a suitable spot in your garden. These are attractive features that will support a range of alpine plants and herbs.
You can also make a purpose-built hibernaculum that will attract amphibians and reptiles. To do this, you will need a spade, log and branches, rocks and bricks, and two or three drainpipe cutoffs (with roughened insides so they are not too slippery for creatures to climb out of. Use sandpaper to create a rough grippy texture, or alternatively use cement pipes).
Pick a sunny spot in your garden, and dig a hole about half a metre deep and one and a half metres wide. Fill it in with the logs, branches, bricks and rocks, making sure there are plenty of gaps and crevices in between. Insert the pipes at ground level into the hole to provide entrance and exit points, and loosely cover up the hole with soil.
If you wish, you can also sow flower meadow seeds and grasses over the top of the mound. This will not only look attractive but also attract bees and butterflies in the summertime.