The urge to mate will bring frogs in from the cold

Picture: Sam Taylor
Picture: Sam Taylor
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Take a walk along a forest or other track at this time of year and it won’t be long before in adjacent ditches you’ll encounter freshly deposited frog spawn.

For many people it is the first true indication that spring has arrived and that hot days and long summer evenings are only just around the corner. But at the moment the nights are still cold and despite only recently having emerged from hibernation, the frogs frequently spawn even when there is broken ice covering the water’s surface. During mating, the smaller male clings to the back of the female and fertilises the eggs externally as they are passed into the water.

The familiar jelly-like mass of spawn helps provide insulation during freezing spells, protecting the black dots of eggs inside and also keeping them slightly above the ambient temperature so as to speed development. It is easy to miss the adult frogs during spawning, for the actual breeding period can be brief and may last only a few days.

The best time to see these mating congregations is in mid-morning when the sun is shining – the frogs love the warmth it brings which spurs them into activity, with there being much resonant croaking which can sometimes be heard from up to a hundred yards away if the air is still. Approach too close and the croaking stops. Closer still and there will be a swirl of water as the frogs dive for safety to the bottom of the pond or ditch.

The eggs develop quickly, the small black spheres turning into elongated mini-tadpoles, which eventually wriggle free after two or three weeks, the time taken being dependent upon the temperature. As spring turns into summer, numerous tadpoles succumb when some of the ditches and shallow puddles where they live dry up. But many more make it and by the end of August large numbers of fully developed froglets begin to leave the water, often timing their departure with heavy rainfall. At this time, the ground can be covered with tiny frogs as they move into the surrounding vegetation, and such large and sudden movements is the source of the long-held belief that frogs can rain from the sky.

During the spring and summer many adult frogs will have moved away from their breeding ponds, but will still generally be found in damp areas. Here they will feast on slugs and snails and other small invertebrates, making them the gardener’s friend. Frogs are particularly frequent in our upland areas, especially those that are clad in heather because of the shelter it provides, and it is not uncommon for a walker to come across several adults in the course of a day’s outing in the hills. I have even found them up to 3,000ft on the high plateau between Glen Clunie and Lochnagar.

These hill frogs often show great variation in colour, ranging from brick-red through to the more familiar tones of green and onto sombre grey-browns.

In many parts of Scotland frogs are localised, and as land is drained for development, their breeding sites disappear. In England, the disease ranavirus, or ‘red leg’ as it is sometimes known, has depleted numbers in some areas, but thankfully this does not seem to have been an issue in Scotland, so far. On the plus side, an upsurge in the number of ponds in people’s gardens has undoubtedly helped our frogs, especially in urban areas.

According to Sam Taylor of the national wildlife charity Froglife, there are all sorts of things that people can do to encourage frogs in their gardens, or in local parks and other outdoor areas.

“Digging a pond is a great help, as well as creating a log pile, leaving areas of long grass or gardening organically – all of which will create places for frogs to hide and look for food,” she says.

Froglife is also launching a smart phone app this spring asking people to go out and spot amphibians and reptiles and to record their sightings, thus enabling the organisation to identify key areas for the animals and plan effective conservation action for the future.

www.froglife.org