ECOS 40(4): Postgraduate winner: Great crested newts: the modern canary in the coal mine

In recent years great crested newts have declined rapidly across the UK despite measures in place to conserve them. The loss of great crested newts is a warning sign of larger scale wildlife loss. If we act now we can help to reverse the trends we have so far observed across taxa.

Many people will be familiar with the great crested newt (Triturus cristatus). Some may be familiar with it through interactions in their garden ponds or through ecological surveys through its range in the UK. As a European Protected Species (EPS) it has special protection under both the Habitat’s Directive and the 1981 Wildlife and Countryside Act, with a licence needed to disturb or harm the animals. With this protection and a widespread distribution, comes a price and so the great crested newt has become the ‘nemesis’ for building developers who wish to take parcels of land and turn them into housing estates. At present we are witnessing a change in the licencing system that governs this process and the protection of newts. The system is moving away from one that regards every newt as precious to a system where ponds and large populations are regarded more important than smaller, less viable ones. This of course has struck a chord with many but there are deeper problems that go far beyond that of the newts.

Agricultural intensification, house-building pressures, and pond loss

Since the 1950s, the number of ponds in the UK has dropped dramatically [1]. Once a commonplace feature on agricultural land, these ponds were filled in as a means of increasing yields in post-war Britain. As agriculture intensified and habitat was lost, species that were previously common started to become rarer. The humble great crested newt was one of these species. Their initial protection under the 1981 Wildlife and Countryside Act was a result of an effort to save ponds, with the newts acting as an umbrella species. If you were able to save a population of newts, then you were able to save the dragonflies, damselflies and other aquatic life that it contained. Umbrella species are still an important part of modern day conservation, especially when they are large and charismatic and can therefore attract sizeable donations [2]. In terms of the newts, this was seen as a brilliant ethos but unfortunately it too may be seen as flawed. Growing pressure from government to meet housing targets has seen prime newt habitat destroyed as a consequence. So what went wrong and how can we try to fix things?

Breaking newts

Like all native amphibians, great crested newts only come to ponds to breed. This occurs once a year at the start of spring. Outside of the breeding season you are less likely to see mature individuals swimming around in ponds, instead they are hunting in the terrestrial environment. Now, picture this… You’ve got a landscape dotted with ponds, some small and some large. A high density of ponds is ideal for newts but what happens when some are filled in or the connecting habitat between them is lost? The dynamics of that metapopulation shift with some ponds becoming sinks (effectively removing animals from the breeding population) and others remain sources (driving recruitment in that population). It’s these sources that need to conserved as they are the areas where newts can successfully breed and colonise new ponds from [3]. The ponds within a metapopulation complex like this will be in a constant flux of sink and source. Sinks may be having too much of a negative effect on the population unless intervention successfully transforms them back into sources. This may be completed by the simple act of reconnecting the ponds back up to the rest of the metapopulation through sensitive land management for wildlife. Even without touching the ponds the number of great crested newts in a given area can be dramatically altered by removing their ability to disperse and forage within the terrestrial environment.

A pond near Wittenham Clumps, UK – home to one of the country’s most significant populations of great crested newts.

Occasionally the destruction of all the ponds as part of a development project leads to the newts being moved to a receptor site as part of the mitigation. Under normal circumstances, this isn’t usually appropriate due to factors such as the potential spread of disease, but it does still occur. When newts are translocated they often don’t stay where they have been introduced, due to the fact that newts are hardwired to return to their natal ponds. If the receptor site is close by to the translocation site, it’s likely that the newts will try to return to what they perceive as their home [4]. Unfortunately the carrying capacity of a number of potential receptor sites isn’t considered in the planning stage of a translocation and so when the ponds get too crowded, newts wonder off and are likely to be never seen again. Translocations of newts are often long and complicated, which is why developers fear them so much, however their success rate differs from project to project [4].

Frog friendly childhoods

If you ask anyone who was a child in the 1970s or 80s about the number of frogs and toads in the local area where they grew up, they will tell you that the ponds used to be heaving. Nowadays, the opposite seems to be true, so where did all the frogs and toads go? Research conducted in 2016 showed that common toads have declined in the UK by 68% over a 30 year period [5]. What has caused such a drastic decline and how did we miss such a dramatic event? The loss of ponds is a leading cause, as is the threat of mortality that roads pose to migrating toads and other amphibians. Over this time, the number of garden ponds has decreased as homeowners lean towards concreting over greenspace, perceiving it as easier to maintain and safer for young children or pets. As with the toads, the newts and the frogs, the number of invertebrates and other pond life have also declined. When was the last time you went for a long drive and had to remove any number of squished insects from the exterior of your car? It’s probably been a long time as insects numbers have been in freefall for a while [6]. What we’ve accidentally done is create a disturbance in food webs and the top predators, the great crested newts, declined rapidly as a response and the significance of this wasn’t recognised.

Ponds in context – caring for the hinterland 

So what does this decline mean and what can we do about it? Back to the newts and the new district licencing scheme which is being rolled out across England as you read this. The system is based on the Habitat Suitability Index first described by Oldham et al. (2000) [7], which gives a score of the potential for great crested newts to be present in a pond. This score is based on 10 different factors but doesn’t take the terrestrial environment into account. The score itself isn’t completely accurate as the newts haven’t exactly read the rulebook. The wider landscape linking to ponds and wetlands isn’t only important for newts but also for insects, birds and other taxa too. In order to reverse the declines we have seen across the board in recent years, we need to recognise the issues and address them – using the great crested newt as a biological indicator. The terrestrial habitat around ponds needs to be protected as much as the ponds themselves are from damage. This requires legislation and guidance to recognise that ponds aren’t the only important habitat for newts. Long grass, hedgerows and other such features are just as vital for the survival of nature across the landscape.  

References

1. Heath, D. J. & Whitehead, A. (1992). A survey of pond loss in Essex, South-east England. Aquatic Conservation: Marine and Freshwater Ecosystems, 2(3), 267–273.

2. Bennett, J. R., Maloney, R. & Possingham, H. P. (2015). Biodiversity gains from efficient use of private sponsorship for flagship species conservation. Proceedings of the Royal Society B: Biological Sciences, 282(1805), 20142693.

3. Griffiths, R. A. & Williams, C. (2000). Modelling population dynamics of great crested newts (Triturus cristatus): a population viability analysis. Herpetological Journal10(4), 157-163.

4. Edgar, P. W., Griffiths, R. A. & Foster, J. P. (2005). Evaluation of translocation as a tool for mitigating development threats to great crested newts (Triturus cristatus) in England, 1990–2001. Biological Conservation, 122(1), 45-52.

5. Petrovan, S. O. & Schmidt, B. R. (2016). Volunteer conservation action data reveals large-scale and long-term negative population trends of a widespread amphibian, the common toad (Bufo bufo). PLoS One, 11(10), e0161943.

6. Hallmann, C. A., Sorg, M., Jongejans, E., Siepel, H., Hofland, N., Schwan, H., Stenmans, W., Müller, A., Sumser, H., Hörren, T., Goulson, D. & de Kroon, H. (2017). More than 75 percent decline over 27 years in total flying insect biomass in protected areas. PloS One, 12(10), e0185809.

7. Oldham, R. S., Keeble, J., Swan, M. J. S. & Jeffcote, M. (2000). Evaluating the suitability of habitat for the great crested newt (Triturus cristatus). Herpetological Journal, 10(4), 143-156.

Cite:

Allain, Steven “ECOS 40(4): Postgraduate winner: Great crested newts: the modern canary in the coal mine” ECOS vol. 40(4), 2019, British Association of Nature Conservationists, www.ecos.org.uk/great-crested-newts-the-modern-canary-in-the-coal-mine/.

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