Migration

Migration Season

Under the influence of hormonal changes the amorous toads start migrating towards water, where they mate and lay their long strings of spawn. We generally see the start of the spring migration on mild nights from about Valentine’s Day onwards. Very little activity is observed at temperatures below 6oC. Depending on weather conditions the migration can continue until mid May. After successfully mating the toads start their arduous return journey back to their permanent summer habitat, where they can be found from March through to September. Young toads will usually inhabit different summer territories to the adults, generally in dense vegetation. In the Autumn the toads will migrate to their winter hibernation sites.

Preparation

In the last few years several hundred metres of temporary polythene drift fencing (figure 1) have been used successfully in parts of the site. Animals can be found more easily and in most cases apprehended before they attempt to cross the roads. Where the fencing is used the casualty rate is virtually nil, but it is unsightly and its annual erection very time consuming. To be effective the base has to be dug into the ground for its entire length. Temporary fencing of this nature can easily be vandalised and is prone to wind damage which necessitates constant maintenance. Recently we have used fine mesh Netlon in localised areas which is proving to be more effective than the polythene, but is more costly.

Unfortunately it is only practical to have the fencing in position during the adult spring migration season, this leaves the summer migrating ‘toadlets’ and autumn migrating adults almost totally unprotected.

fence drain

Road drains can kill a large number of toads and other amphibians. Once the toads fall in, the only means of escape may be along the pipe leading from the drain chamber. Distances to the outside world can vary from a several metres up to several hundred. The dangers are made worse by the increasing use of kerb stones that channel amphibians towards grating covers. Temporary measures can help to protect amphibians. A fine mesh Netlon® placed under the grill to prevent entry with a simple raft and stake proves effective (figure 2).

The construction of an amphibian tunnel (completed December 1995) at one of the main crossing places has proved a success. The tunnel is not fully operational due to the lack of suitable funneling drift fencing, funds permitting this is something we hope to improve in the near future. The only practical way to reduce the high number of ‘toadlet’ fatalities is through a comprehensive system of tunnels, linked to permanent fencing. We envisage a further three tunnels in the future.

Collection

On evenings when the temperature is above 5.5oC from dusk onwards volunteers search for toads as they approach the roads, collect them and sort them into buckets depending on which direction they are moving. Toads are particularly sensitive to salts, so it is important that they are handled carefully and quickly placed into buckets. The search for toads is made easier by the use of powerful lamps and we recommend that all our volunteers wear reflective jackets. During the breeding season it is fairly easy to sort the males from the females. Males have black roughened pads on their inner two forefingers that help them to grasp the females, so their hands have two pale and two dark ‘fingers’. All the females ‘fingers’ are pale. Generally females tend to be larger than the males and their skin has a slightly different appearance.

Counting & Release

We try to keep a fairly accurate count of the number of toads and other amphibians collected to give an insight into the size of the population and the importance of the site. Also by counting them going to the ponds and comparing the returning numbers we get a fairly good indication when the spring migration is over and it is safe to remove the temporary fencing.

Confusion can arise mid season when there is a considerable overlap between the toads going to breed and those returning to their summer habitats. Females leave the breeding site immediately after laying their spawn. Unfortunately it is quite difficult to tell which females have bred and which have not, as bred females can puff themselves up with air giving the impression of being full of eggs. Apart from the ‘deflation technique‘ which should only be practiced by experts, bred females can be identified in two ways. Firstly, a bred female if examined in good light will often have a faint brown mark near each of her armpits where the male has grasped her. Secondly, when a gravid (pregnant) female is picked up, she will often sit quite still with her legs tucked in displaying a receptive posture to males. If we are unsure whether a female has bred or not we will return her to the lakes. Males tend to remain at the lakes until all or most of the females have returned.

We have release sites close to the lake sides where the toads are able to quickly re-orientate themselves to their surroundings. If a female is surrounded by males it is advisable not to place her in the water as she could drown. Extreme caution should be practiced when approaching the release sites as large numbers of males are often waiting in these areas.

Toads returning to their summer habitats are released at a safe point the other side of the road, near to their rescue points in the same area of the village. If the temperature is beginning to drop, it is important to release the toads near to some natural cover so that they are not exposed to frosts.

Importance

In a recent survey only eight British sites including Madingley were reported where more than 1000 animals were assisted in one season, thus highlighting the importance of this site. In addition to toads, other amphibians rescued include the protected great crested newt, smooth newts and frogs.

If managed properly Madingley’s important amphibian population has the potential to survive indefinitely. This can only happen with adequate support and funding, without which the region would lose an important part of it’s natural heritage.