4. With regard to overall numbers it is possible that the development may have temporarily helped increase the local population. We have no data on the amphibian population before the development started but a substantial area to the north of the pond has been temporarily allowed to revert to scrub thereby improving terrestrial habitat and the pond itself has nearly doubled in size.

To sum up although the figures show large numbers of amphibia caught in drains this may be partly the result of their being forced to head for a single, unfamiliar, site which has been surrounded with every obstacle, hazard and pit fall imaginable. One has to admire the animals' persistence in getting there at all!

It would require more intensive monitoring than we were able to conduct to gain a precise figure for the percentage of migrating toads that were being trapped. It was certainly far more significant than the numbers being run over. We never saw more than five road casualties and usually less on any one evening. On March 18, however, although all the drains were cleared at dusk and all visible toads moved, 5 had fallen into drain B by 2130 hrs though what proportion that represented of the total on the move is difficult to say. Our guess is at least 10% of the toads trying to cross the roundabout were caught.

Drain B and the most productive drain in the car park were all next to kerbs too high for toads to climb. The road to the car park from the roundabout, however, had a number of ramps flush with the top of the kerb but plenty of toads managed to fall down a drain directly adjacent to a ramp. Likewise there is no kerb at all by the drains on the Kennel Farm road and yet frogs and toads seemed to fall down them with monotonous regularity. The road is little used and the toads, may be, were in the habit of walking along it or alternatively the drains happened to be at a preferred crossing point. At all events making it easier for amphibia to negotiate kerbs may mitigate but not eliminate the drain problem.

The same applies to devices placed in the drain to enable amphibia to climb out. As already mentioned toads were often in amplexus and mating balls of three or more were not uncommon. It seems that trapping animals together in the drains increases the likelihood of these clusters forming. Females are unable to climb out under such circumstances and the males hang on long after the female is dead.

CONCLUSION

Balancing ponds are, we gather, increasingly being constructed in new housing developments. It would be interesting to know if similar ponds have generated comparable amphibia colonies. If there is any likelihood of their doing so then various design features could easily be incorporated to overcome at least some of the problems detailed above.

The new road will greatly increase traffic and much of the present terrestrial habitat will disappear. Approaches are being made to the County Planning authorities via the IVCP to see if tunnels, or other measures, can be constructed under or beside the road. By coincidence one firm dealing with such items, ACO Wildlife, Shefford, is local to the area. There is also the possibility of constructing a pond in the proposed linear wood. Next year there will be time to organise proper toad patrols if there is sufficient response.

AFTERWORD

The April rain brought out plenty of small frogs and a number were observed in the drains particularly in the opening of the side pipe. Removing them was tricky and we wondered if it was worthwhile. The Telegraph Magazine of 11 April 1998 has an interview with a sewer Operations Assistant responsible for the North East London area which mentions large colonies of frogs in some sewers. Are the frogs happy to live there?

ACKNOWLEDGEMENTS

We would like to thank the unknown lorry driver mentioned above; the receptionist and staff at the District Council offices in Biggleswade for their courtesy in answering our questions; and the manager of the swimming pool for facilitating our access to the pond.