Toads in the city

- 9:15 pm - July 18th, 2016


On 1st July 2016 a group of Novatech delegates were taken to a series of developments in Villeurbanne, Lyons, where innovative green infrastructure was being used to achieve multiple objectives including stormwater management.  One of the most unusual was a new housing development which had been stopped 9 years earlier when a population of the midwife toad (Alytes obstetricans) was discovered there.  This small toad is unusual in that the males carry the fertilised eggs entwined around the hind legs until ready to hatch, when he drops in a pond or slow-moving water and they are released as tadpoles.  At the housing development, the plans had to be re-assessed and a mitigation plan developed in conjunction with the developers and nature conservation experts.  A grass swale through the development replaced a conventional stormwater sewer, and use of open grill gully traps was minimised.  Natural vegetation replaced the original planting plan, with oak trees and grass meadow features.  The toads naturally frequent stony loose soils and river margins, so banks of stone filled refuges have been provided around the development, alongside the swale but also within green space elsewhere for the terrestrial phase of the toads’ lives, to provide protection from predators such as domestic cats, and places to escape the glare of the sun.  Where the main swale is crossed by a road through the housing estate, a ‘crapauduc’ has been built (a toad tunnel) to allow safe movement of the toads and other amphibians.  It is hoped that the quality of runoff should be mitigated by the grass and gravels in the drainage features.

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Toadlets metamorphosed from tadpoles translocated from original breeding pond, the crapaud tunnel beneath the main road in the housing development, and Olivier Montavon explaining the toad shelters alongside the swale


Reference:  Montavon O and D’Arcy BJ, Saving the midwife toad in Lyon, The Geographer, Royal Scottish Geographic Society, RSGS, autumn 2016 (in press)