Tuesday 03 February 2009

Help frogs through the cold snap

By Phil Bowles

With freezing temperatures again holding Britain in their grasp, spare a thought for the amphibians riding out the cold snap at the bottom of your garden pond.

As ponds are being lost and amphibian populations decline in rural areas throughout the country, urban ponds are becoming increasingly important for the survival of several species. In particular, they may provide critical overwintering habitat for common frogs (Rana temporaria), which often seek shelter at the bottom of ponds to avoid freezing during the colder months.

During prolonged cold spells, however, ice cover at the pond’s surface results in the build-up of waste gases and a shortage of oxygen in the water below. The resulting anoxia is fatal to pond wildlife including frogs and fish, leading to a phenomenon known as ‘winterkill’.

Fortunately, there’s a simple way to help the frogs in your garden avoid winterkill events. Lucy Benyon, Wildlife Information Officer at the amphibian and reptile charity Froglife, explains: “To stop winterkill happening in your pond simply ensure that there is a hole in the ice for pond gases to escape.” However, she emphasises that some common methods for keeping ponds ice-free – the use of salt or other chemicals, pouring hot water over the surface, or physically breaking the ice – are all potentially damaging to pond life, and so should be avoided.

Instead, Froglife recommends placing a plastic ball in the pond overnight as a wildlife-friendly alternative. As ice freezes around the object, it will leave a ready-made hole when you remove the ball in the morning. If the pond is already iced over, another solution is to place a pan of hot water on the surface and allow the hot base of the pan to melt the ice beneath.