Toads much in evidence

Even though I have had little time to spend working in the garden this summer, I seem to have seen the resident toads more frequently than in previous years. Last thing at night I have often come across one on the gravel path that snakes its way up the garden. Sometimes one can be seen on the patio, where it attracts the passing interest of the dogs and, occasionally, one appears outside the back door causing my heart to skip a beat as I almost tread on its vulnerable form.

The toads have never bred in the garden, the pond perhaps too small and dominated by other amphibians, whose tadpoles would out-compete those of a toad, but they have been ever-present since we moved in here more than a decade ago. There are larger ponds in nearby gardens and these may be the source of the smaller toads that are seen from time to time in the garden, for it is the larger individuals that are most often encountered. The largest of these may well be females, the bigger of the two sexes. The two sexes are fairly similar in appearance, though the warts are less prominent on the female and the toes of the front legs more delicate. Mature males develop characteristic pads on their inner toes during the breeding season, these being used to grip the female.

Common toads are terrestrial in habits for most of the year and seem well adapted to life on land. The garden almost certainly holds sufficient prey to support several toads and I suspect that our resident population is, judging by the sizes encountered, a mixture of immature and mature individuals – maturity is reached three or more years of age in females and two or more in the males. One particular individual must hide up near the shed, for it is often seen here during early evening. Although the background colour of her skin (I think of this particular toad as a female) changes with the light, from dull olive green to a warmer green-brown, she has a characteristically-shaped black splodge behind her right eye. The most colourful feature is the eye, a black horizontal pupil bordered by a yellow-orange iris, which darkens where it meets the horizontal to create a three-dimensional effect and the illusion that the top part of the iris is jutting out like a baseball cap.

Seen close-up, best accomplished by lying prone on the ground next to the toad, the delicate pattern of the warts can also be seen, as can the paratoid glands, positioned behind the eyes. It is from these that the toad can release its foul-tasting toxin. Little wonder the dogs leave them well alone.

Unexpected visitor raises a question or two

It came as something of a shock the other morning to discover a toad sat in the middle of the kitchen floor sporting a look of passive acquiescence. I was still bleary-eyed, roused from sleep by two dogs intent on their morning walk, and there it was, sat on the carpet, raising the question of how it had made its Houdini-like appearance in my kitchen. Needless to say the dogs were decidedly non-plussed, having developed a grudging respect for toads at a young age. Anything that can inflate itself and exude an unpleasant chemical when approached by an overly-inquisitive puppy soon earns respect. I picked up the toad and deposited it in the garden. The toad was a youngster, not a toadlet but a two-inch long juvenile from last year. I suspect that it had clambered up the pipe that links the outlet from the washing machine to the outside drain but while this answered the question of how it had got into the kitchen it did raise the question of where it had come from.

Like our other amphibian species, the common toad is dependent upon water for breeding but at other times of the year it can be found in gardens, woodland and even grassland. Research into the ecology of the common toad has revealed that individuals typically overwinter within a 1,000 metres or so of their breeding pond. Since our small wildlife pond only ever has frogspawn, it seems likely that there is a suitable breeding pond nearby, and that this individual came from there. Toads favour larger-sized ponds than frogs, with an optimal size being about 1,000 square metres, with plenty of marginal cover. They also seem to prefer ponds containing fish, perhaps because fish find their tadpoles unpalatable but will feed on the newt and frog tadpoles with which the toads compete. Deliberate attempts to introduce common toads into garden ponds invariably fail so competition with other amphibians may not be the only reason why we see adult toads in our gardens but not breeding in our ponds.

There is an interesting footnote to this episode. Last year, our new neighbours were figuring how to convert a rather large and overly deep pond into something more wildlife friendly. The previous owner had dug the pond in the expectation of populating it with carp but never did. He only managed to fill it with water just prior selling the house. Before the pond could be adapted several strings of toad spawn appeared followed by a number of tadpoles. With no vegetation within the pond these soon perished and that was that. Perhaps a new and bigger wildlife pond might tempt them to breed again.

Roads take heavy toll on toads

Heading out of Thetford on Sunday I came across the sad sight of a dozen or so common toads squashed on the road. The corpses were all concentrated along one twenty-foot stretch, a crossing point used by the toads on their annual migration to a local breeding pond. Over the coming nights it seems inevitable that other corpses will be added to the sickening toll, as more toads reach the road and attempt to cross. One of the reasons why common toads seem so susceptible to motor traffic is their habit of crawling a few feet and then resting for several minutes before continuing. Although the scene will be repeated on other stretches of road close to breeding ponds, there have been efforts to reduce mortality levels through the erection of warning signs and the designation of registered toad crossings. It is hard to estimate the impact of traffic-related mortality on the toad population but, from the handful of studies that have been carried out, it appears that many populations can compensate for the annual losses since the populations remain stable over time.

We have our ‘own’ toad that frequents the patio and borders on warm summer nights and frightens our over-inquisitive dogs by adopting a defensive posture. I do not know where this particular individual breeds but it may use the pond next door, where toad spawn was in evidence last year. Our own smaller pond is deemed unsuitable and just supports the local frogs (spawn first appeared on 26^th March).

Common toads are only dependent on water for breeding and outside the breeding season spend little time in the water. Instead, they search for prey in gardens, rough grassland and even woodland. This means that your best chance of viewing these creatures is during late March and early April when they gather at the breeding ponds. The smaller males outnumber females at these gatherings because not only do they mature at a younger age but they arrive first and remain longer at the ponds. Sometimes there may be ten males to each female, which means that competition for a mate can be intense. Males attempt to grasp a female and position themselves so that they can fertilise her spawn. Other males try to break the embrace and manoeuvre themselves into position so it can all get rather chaotic, with over-enthusiastic individuals grasping at other objects including goldfish, vegetation and other males. Unlike frog spawn, toad spawn is formed in strings and is wrapped around the vegetation. The emerging tadpoles, like their parents, use toxins to deter would-be predators and this may be why they are successful in ponds containing fish, where frogs usually fail.