Why did the toad cross the road?
You may have read online or in a newspaper last month that common toads (Bufo bufo) have declined in Britain by nearly 70% in the past 30 years. This decline is unprecedented with such a widespread and ubiquitous species within the industrialised world. There are a number of reasons for the declines observed of which I shall delve into more detail later. When I first heard the news I was in Malaysia and the news took be aback slightly. I’m heavily involved with the monitoring of amphibians (and reptiles) in Cambridgeshire, we’ve observed declines in recent years but nothing as drastic as 70%.
A major cause for declines of common toads is habitat loss. Their breeding ponds (which are also used by other amphibians) are drained to build houses, improve infrastructure or to expand agriculture. The associated terrestrial habitat they also rely on to forage is also converted, despite it being important for the survival of adults and juveniles. If roads are built through prime toad habitat, this may lead to fragmentation between the terrestrial habitat and breeding pond. Here toads will encounter an obstacle which has also been attributed to major declines, cars. Thousands of toads die each year when they migrate to or from their breeding ponds and are faced by roads. Thankfully there are volunteers such as myself to help toads cross these roads safely. Despite this huge national effort, roads are still causing huge declines in toads. Maybe it’s time we change how we build and design roads, taking wildlife such as toads into account.
Common toads spawn in their natal ponds and lakes, meaning that the same toads return to the same ponds year after year (assuming they don’t perish between breeding seasons). Even if the pond disappears, toads will still migrate to where the pond used to be. If the pond isn’t removed, then it may become polluted with farm run off such as pesticides and fertilisers which will have different effects on the ecosystem. Pesticides will poison the amphibians and other life, whilst the fertilisers will promote the growth of algae causing eutrophication. Both of these are additional factors that can lead to small localised declines. Localised declines and extinctions soon add up to those observed nationally.
There are another smaller impacts affecting toad populations such as disease, road salting and spawn failure. Climate change is expected to only make the declines worse. Evidence suggests that milder winters leads toads coming out of hibernation in a less vigorous state. Some winters toads won’t hibernate as the environmental cues needed aren’t there – they therefore use up their fat reserves as food is scarce. There are other effects that we are only just beginning to understand. It’s clear that without intervention toads are set to decline further – perhaps they’re a species that will be restricted to only a handful of sites in 20-30 years time similar to the natterjack toad? This speculation is assuming a worst case scenario, I’d be heartbroken if they were lost from the majority of the British landscape. Now is the time to act!
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