The common frog Rana temporaria is a familiar sight across the UK. In any shallow standing water you are likely to come across tell-tale clumps of spawn, and tadpoles and froglets vying for survival, not above eating their siblings if needs must!
But just when can you expect to find frogspawn and tadpoles in your local pond? The simple answer might be spring for spawn, and summer for tadpoles, but delve deeper and this doesn’t quite stand up to scrutiny.
|Early frogspawn on The Lizard|
|Frogspawn on Predannack Airfield Nov 14|
Thanks to the long history of phenology in the UK, in which the date of first frog spawn features strongly, records like this from the Lizard can be put to good use. The UK phenology network has morphed in recent years into the website www.naturescalendar.org.uk , hosted by the Woodland Trust, and supported by a huge network of enthusiastic amateurs submitting records ranging from first bluebell of the year, to first redwing and last swallow. This website has some excellent time lapse maps showing frogspawn’s march north and eastwards in any given Spring. 70,000 first frog spawn UK dates 1998-2007 were analysed and this revealed that, starting in the far south west, spawn took 7.5 days to ‘march’ 100km eastwards, and 5 days to advance 100km northwards. Comparison with data from 60 years before showed spawning to be 10 days earlier, a symptom of global warming, as early spring temperatures are a critical control on spawning dates.
And for tadpoles? Don’t be surprised if you find them in December too! Reports of tadpoles overwintering in ponds have been reported from Cornwall and Kent in the south, to Aberdeen in the north (see www.theguardian.com/theguardian/2010/nov/17/tadpoles-over-winter-in-pond). Research from Edinburgh and Glasgow Universities suggests this isn’t, as was once thought, a case of tadpoles failing to make the grade, but more a strategy chosen to allow the individuals to get ahead as, when they finally become frogs in Spring, they are a larger size. Some individuals may be taking advantage of the milder winter temperatures, from global warming, to become bigger tadpoles, and hence larger frogs.
So keep your eyes peeled, and records flowing in. You never know quite what time of year you may find frogspawn and tadpoles!