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What our animals are doing this month….

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May is an excellent time of year to look out for our native legless lizard, the slow-worm. Breeding takes place in May and this can be a dramatic process to witness. Not only do males compete aggressively over mates, but during courtship they will grasp the female roughly by the neck, and mating can then last for up to 10 hours! Courtship is easily mistaken for fighting, so being able to tell males and females apart can be helpful. Male slow-worms are grey or brown all over, and some have bright blue spots along the back. Females are usually brown on top with dark sides and belly, and a dark line down the back.

Slow-worms are a common garden species and the perfect gardener’s friend, as they love to eat garden pests such as slugs. They are particularly fond of compost heaps and warm hiding places such as log piles or under tin roofing, so these are good places to look for them. Despite their snake-like appearance, slow-worms can be distinguished from snakes by their shiny appearance, bullet-shaped heads, and blinking abilities (snakes lack eyelids!)

 

A pair of courting slow-worms (Photo: Lin Wenlock)

Ponds Against Climate Change

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From Antarctica to the tropics, ponds are widespread habitats found in nearly all terrestrial biomes (Jeffries, 2016). Research estimates that there are 304 million natural lakes and ponds worldwide, covering a total area of approximately 4.2 million km2 (Downing et al., 2006). This article will focus on ponds: according to limnologists, the difference between ponds and lakes is that ponds are shallow enough that plants could grow across the entire surface meaning that it has a photic zone where sun can reach the bottom. By contrast, lakes have an aphotic zone meaning there are sections deep enough that sunlight cannot reach the bottom. Ponds are biodiversity hotspots for both aquatic and terrestrial species, providing habitat for rare specialists such as fairy and tadpole shrimp. Not only are they vital for these species, but they are also vital in managing landscapes from threats such as flooding and climate change. It is known that aquatic ecosystems have a large role in managing greenhouse gases, with oceans among the most well-known of carbon sinks. However, with lakes and ponds covering such a vast expanse of area, is it possible that they are the climate’s unsung heroes?

Carbon sinks are reservoirs that absorb and store atmospheric carbon through physical and biological processes. One study concludes that ponds may be more active in nearly all of these processes than large lakes, marine ecosystems and terrestrial ecosystems (Downing, 2010). Carbon burial rates between ponds can vary depending on composition. Ponds are not ubiquitous, thus the effectiveness of carbon sequestration varies per site depending on factors such as substrate type and vegetation. Gilbert et al., (2014) found that permanent and naturally vegetated ponds were the most efficient at sequestering carbon dioxide, particularly those dominated by thick moss swards and aquatic grasses. These form a thick, moist blanket when the pond dries out, minimising the release of stored carbon into the atmosphere. The least efficient ponds were temporary, shallow arable ponds which lacked vegetation and were regularly disturbed. When discussing the value of ponds in carbon sequestration, it may be unhelpful to group all ponds together as their importance can vary considerably based on their composition. Furthermore, it is important to note that ponds can serve a variety of purposes. Whilst ponds capturing excess fertilisers and pesticides are useful in the fight against climate change, they may not make good wildlife ponds or facilitate biodiversity.

This diversity of ponds is reflected in the range of carbon sequestration rates found across the literature. One study found that small ponds sequester 79-247g of organic carbon per square meter annually, a rate 20-30 times higher than woodlands, grasslands and other habitat types (Taylor et al., 2019). Céréghino et al., (2014) suggested that some 500m2 ponds may even be capable of sequestering up to 1000kg of carbon per year, as much as a car would produce in that time. Although ponds only take up 0.0006% of land area in the UK, a tiny proportion compared to the 36% of grasslands (Carey et al., 2008), their high rates of carbon burial suggest that their overall contribution is significant – even when compared to much larger habitats. Thus their role in tackling climate change should not be overlooked.

Biological processes carried out by aquatic vegetation are pivotal in carbon sequestration in ponds. Photosynthesis contributes to the sequestration of carbon dioxide by turning it into oxygen and biomass. One kilogram of algae uses an average of 1.87 kilograms of carbon dioxide a day (Anguselvi et al., 2019). Algae in ponds also contribute to reducing additional greenhouse gases such as nitrous oxide (N2O). Nitrogen is a key component in chlorophyll and thus used in farm fertiliser. Excess nitrogen could react with oxygen in the air to become N2O. The presence of algae in farm ponds to capture this excess can prevent this reaction from occuring and limit emission of the greenhouse gas. A study has found that two thirds of farm ponds act as N2O sinks (Webb et al., 2019), making them an important contributor to combating climate change, particularly as N2O traps heat at 300x the rate of CO2. 

Ponds play an important role in mitigating climate change, however, there is evidence to suggest that they can also act as carbon sources. Does this offset their sequestering benefits? Take for instance, permafrost thaw ponds. Permafrost thaw ponds in northern regions can be particularly prominent sources of carbon. As permafrosts thaw, vast amounts of carbon dioxide and methane are released, resulting in the formation of small ponds which become carbon emission hotspots (Kuhn, 2018). Although they are releasing carbon, it is not the pond itself creating these gases. Global warming is causing the permafrosts to thaw out and release the stored carbon. Although the ponds facilitate the emissions, it is perhaps misleading to label them as a carbon source in these instances. 

Large habitats such as oceans and woodlands are well-known for their role in reducing greenhouse gasses and mitigating the effects of climate change, but ponds may play an equally important and largely underappreciated role. Ponds are also a fantastic tool against climate change because they give people a way in which to take action. People can easily create ponds in their own gardens and community spaces, and in this way play a part in reducing greenhouse gas emissions and contribute to the global fight against climate change.

Written by Mirran Trimble & Emily Robinson

 

References

Anguselvi, V., Masto, RE., Mukherjee, A., & Singh, PK. (2019) CO2  Capture for industries by algae, Algae, Yee Keung Wong, IntechOpen, DOI: 10.5772/intechopen.81800. Available from: https://www.intechopen.com/books/algae/co-sub-2-sub-capture-for-industries-by-algae

Carey, PD., Wallis, S., Chamberlain, PM., et al. (2008) Countryside Survey: UK results from 2007. Swindon, UK: Natural Environment Research Council.

Céréghino, R., Boix, D., Cauchie, HM., et al. (2014) The ecological role of ponds in a changing world. Hydrobiologia. 723, 1–6.

Downing, JA. (2010) Emerging global role of small lakes and ponds: little things mean a lot. Limnetica. 29(1), 9-24.

Downing, JA., Prairie, YT., Cole, et al. (2006) The global abundance and size distribution of lakes, ponds, and impoundments. American Society of Limnology and Oceanography. 51(5), 2388-2397.

Gilbert, PJ., Taylor, S., Cooke, DA., et al. (2014) Variations in sediment organic carbon among different types of small natural ponds along Druridge Bay, Northumberland, UK. Inland Waters. 4(1), 57-64.

Jeffries, MJ. (2016) Flood, drought and the inter-annual variation to the number and size of ponds and small wetlands in an English lowland landscape over three years of weather extremes. Hydrobiologia. 768, 255–272.

Kuhn, M., Lundin, EJ., Giesler, R., et al. (2018) Emissions from thaw ponds largely offset the carbon sink of northern permafrost wetlands. Scientific Reports. 8, 9535.

Taylor, S., Gilbert, PJ., Cooke, DA., et al. (2019) High carbon burial rates by small ponds in the landscape. Frontiers in Ecology and the Environment. 17(1), 25-31.

Webb, JR., Hayes, NM., Simpson, GL. et al. (2019) Widespread nitrous oxide undersaturation in farm waterbodies creates an unexpected greenhouse gas sink. PNAS. 116(20), 9814-9819.

 

Should we count marine turtles as members of the British fauna?

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In August 2020, the media outlet Wales On-line reported that a five-foot long marine turtle had surfaced beside a small fishing boat off the north coast and swum alongside it for an extended period before diving out of sight. The excited boat owner said that he had fished those waters for over 20 years, and never seen a turtle before. Was this an exceptional sighting? The fisherman was certainly lucky. Over the last century or so, the average number of leatherback turtles (the species observed) seen in British waters each year is around 15. However, this is bound to be a vast underestimate of the turtle numbers actually present in British waters. This is due to them being incredibly difficult to locate as they rarely emerge from the depths to breath, nor do they nest on British beaches; so the chances of actually spotting one in the huge expanses of our coastal waters are very slim.

Botterell et al. (2020) have published an analysis of marine turtle sightings, strandings (usually found dead washed up on shore) and captures (by-catch in fishing nets) since 1910. Of 1997 records, 84% are of leatherbacks; 12% of loggerheads, and 3% of Kemp’s ridleys. The remaining 13 records concern tiny numbers of three more species. Until 1980, records were small in number for all species, with substantial increases from the 1990s onwards. Mapping of the records shows that most are predominantly from the western side, including the English Channel, all around Ireland and north to the Orkneys and Shetlands. Leatherbacks and loggerheads have been recorded at all times of the year, with peaks in June-October (leatherbacks) and November-March (loggerheads). Kemp’s ridleys have only been seen from October-February. Measurements on body size, mostly from strandings and captures, suggest that most leatherbacks in British waters are adults, while loggerheads and Kemp’s ridleys are juveniles.

Although they may seem like an exotic species, these data clearly show that we should regard leatherback turtles as normal members of the migratory fauna that inhabits our surrounding seas. Adult leatherbacks manage this by generating enough heat that their body temperature is above ambient, allowing them to remain active in the cold waters of the North Atlantic; even juveniles can raise their body temperature above cold water temperatures by activity and reduction of heat loss (Bostrom et al., 2010).  For loggerheads and Kemp’s ridleys, the majority of records in British waters are strandings of juveniles in winter: these are most likely animals cold-stunned as water temperature declines. What is unknown is the number which venture into our waters, but manage to travel south and survive.

Marine turtles display what are known as cosmopolitan ranges, meaning that they are near-ubiquitous in waters globally. This has led to their incorporation into indigenous cultures around the world, with their size and habits having led to mythological status in many places. In an ecological context, the extensive migrations they undertake between foraging and nesting grounds (which often span entire oceans) are important for connecting ecosystems globally. The three species commonly found in British waters have distinct breeding and foraging grounds, with much information recently derived from satellite tracking of tagged adult females following capture at nesting sites (Fossette et al., 2014). For example, Atlantic leatherbacks consist of two separate populations. South Atlantic turtles breed either along the coast of Brazil or of West Africa, especially Gabon. Foraging takes them across the ocean and southwards, but not into the North Atlantic. The North Atlantic population breeds on the beaches of southern Florida, the islands of the Caribbean and the Guianas. They forage east and north, as far as British waters, as we have seen. Adult females return to nesting beaches every 2-4 years and lay up to 7 clutches, each 60 – 110 eggs, over several months.

Female leatherback turtle nesting on a beach in Tobago.

The males wait near the approaches to the beaches and attempt to mate with any females that turn up; however, they do not come onto land and instead spend their entire lives at sea. Leatherback females show moderately high nesting site fidelity, with all their nests in a season being laid on the same beach which they were born on or ones in close proximity. Hatchlings disperse into the sea and travel east towards open ocean to develop into juveniles. Kemp’s ridleys nest in the Caribbean, nearly all on one 16- mile Mexican beach; juveniles extend across the North Atlantic. Loggerheads are highly cosmopolitan with three distinct Atlantic populations. In the West Atlantic, they nest on beaches as far north as New Jersey and south to Parana in Brazil. Juveniles forage very widely. The Gulf Stream (also called the North Atlantic Gyre) was thought to be the primary determinant of juvenile distribution, as it carries developing individuals into east Atlantic waters. However, active dispersal has been recently documented in loggerhead, green and Kemp’s ridley turtles which suggests a more selective use of habitat than previously thought (Mansfield et al., 2014).

Sources of nutrition are a key determinant of marine turtle distribution. In other words, they go where the food is. The abundance of jellyfish in eastern Atlantic waters brings adult turtles, including loggerhead and Kemp ridley’s, but especially leatherbacks to UK and Irish coasts. As well as helping to predict the position of leatherbacks, the presence of jellyfish affects the depth at which the turtles swim. Jellyfish display a diurnal pattern of vertical migration, following their plankton prey up and down the water column. Plankton move to the water’s surface at night, when they are less visible to potential predators, and are closely followed by the jellyfish and, in turn, the turtles. Leatherbacks are so committed to pursuing their translucent prey that one intrepid individual was found swimming over 1000 metres underneath the surface during a foraging mission. This feat put leatherbacks into the top three diving animals on the planet alongside beaked whales and sperm whales. Their dedication to pursuing cnidarians was also shown by a 12,000 mile foraging journey from Indonesia to the US, which shows the determination present in their feeding habits.

It is these same feeding habits that have become a source of harm in recent times. Ingestion of marine litter, especially plastic bags, is a leading cause of turtle mortality. Particularly affected are leatherback turtles, due to their specialised diet of jellyfish which closely resemble partially degraded plastic bags hanging in the water column. One study analysed historical autopsy records spanning 123 years (1885-2007) and found plastic to be present in the digestive tracts of 34% of the dissected turtles (Mrosovsky et al., 2009). Plastic ingestion has a range of detrimental consequences, including reduced nutritional intake and asphyxiation.

There is a considerable worldwide effort to conserve marine turtle populations. One measure of this is the regularly updated IUCN Red List.  Since the 1980s, there has been a large reduction in leatherback numbers which has led to a ‘vulnerable’ classification by the IUCN. However, there are subpopulations that are doing even worse, such as those of the northwest Atlantic subpopulation who were reclassified from Least Concern to Endangered in 2019. Another case was a subpopulation based in the South China Sea that produced 10,000 yearly nests on the beaches of Malaysia. However, from the 1960s the population dwindled to the point where only two nests were laid in 2008, both of which were infertile (WWF, on-line). This decrease in numbers was partly made worse by misled conservation efforts, which collected and artificially incubated eggs at excessive temperatures, scrambling the sex determination process. As in many other reptile species, sex is determined by the temperature of incubation of the eggs. This shows the need for in depth research when developing conservation measures to deal with anthropogenic threats.

There is a wide range of barriers to the recovery of turtle numbers, with pressures both natural and anthropogenic. Among the natural threats faced by marine turtles is the impact of climate change on temperature-dependent sex determination, which disrupts reproduction and has knock-on effects on population demographics and dynamics. Another prominent challenge to successful reproduction is the predation of eggs and juveniles, which make for easy pickings for a diverse array of coastal predators.

A group of black vultures patrol a nesting beach looking for hatchlings to prey on.

Conservation efforts and scientific surveys are often based around these issues, when the turtles are onshore and accessible for data collection. Studies focused on the reproductive stage of turtle life are very valuable to the implementation of management strategies and can provide a range of insights into their life histories. The Exploration Society operating out of the University of Glasgow has run many research projects along these lines, based in the Caribbean islands of Trinidad and Tobago. These studies have contributed analyses of egg temperatures, tagging efforts to track distribution and last year uncovered a novel female behaviour for nest protection: after burying the eggs, females create a ‘decoy trail’ aimed at misleading predators over the location of the nest (Burns et al., 2020). All of these contributions are helpful to maintaining healthy populations of turtles, but there is still a large gap in the knowledge of turtle life out in the open ocean.

Leatherback hatchlings burst from a concealed nest, heading to the sea to begin their life of roaming the oceans of the world.

Marine turtles spend most of their lives navigating the oceans, across a massive geographic range and at various depths. This makes them pretty tough to track throughout their development from hatchling to mature adult, and even between nesting events. However, as we have seen, the use of satellite tracking has revealed much about adult migrations. In addition to this, the missing pieces of the puzzle can be cleared up with the help of sighting and stranding data collected from coastlines within their range, which can be acquired through citizen science projects and compiled into databases to map distributions at different stages of development. Stranded carcasses can also be inspected to gain an insight into the causes of death, and the larger scale threats to their survival. For example, carcasses with scars on their shells can show the impact of high densities of fishing vessels. The number of sightings can also be used as an indicator of population trends, as was shown by Botterell et al. (2020), summarised above. Tracking sightings and strandings off the British and Irish coasts, the study was able to attribute dips in numbers to major environmental events such as the Deepwater Horizon oil spill in 2010 and link population increases to successful conservation programmes. This shows that despite the challenges facing this fascinating group of reptiles, we can make use of the full range of analysis tools available to more fully understand their life history; from hatching through juvenile to nesting adult. From this, effective conservation strategies can be developed to protect marine turtles throughout their cosmopolitan range.

References

Bostrom, B.L. et al. (2010). Behaviour and physiology: the thermal strategy of leatherback turtles. PLoS ONE 5(11), e13925.

Botterell, Z.R.L. et al. (2020). Long-term insights into marine turtle sightings, strandings and captures around the UK and Ireland (1910-2018). Journal of the Marine Biological Association of the United Kingdom 100, 869-877.

Burns, T.J. et al. (2020). Buried treasure- marine turtles do not ‘disguise’ or ‘camouflage’ their nests but avoid them and create a decoy trail. Royal Society Open Science 7, 200327.

Fossette, S. et al. (2014). Pan-Atlantic analysis of the overlap of a highly migratory species, the leatherback turtle, with pelagic long-line fisheries. Proceedings of the Royal Society B 281, 20133065.

Mrosovsky, N. et al. (2009) Leatherback turtles: The menace of plastic. Marine Pollution Bulletin 58, 287-289.

Mansfield, K.L. et al. (2014) First satellite tracks of neonate sea turtles redefine the ‘lost years’ oceanic niche. Proceedings of the Royal Society B: Biological Sciences 281, 20133039.

WWF on-line. Search at https://www.wwf.org.my/?25625/Marine-Turtles-Malaysias-National-Heritage

Cameron Boyle, Roger Downie and Jack Rawlinson

Photos generously provided by Jack Rawlinson

University of Glasgow

What our animals are doing this month….

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Adders emerge from brumation in March and April and begin breeding shortly after. Rival males compete for females by performing a dance-like duel where they rise up and wrestle each other to the ground. Although this is an aggressive behaviour between two males, it can look very elegant and is sometimes mistaken for a courtship ritual.

Females incubate eggs internally and ‘give birth’ to live young. They will sometimes mate with multiple males in a breeding season, and some years will not breed at all if conditions are not right.

Adders are venomous, but their bites are rare and generally not serious. They are shy and will only bite as a last resort if threatened. Saying that, adder bites are most common at this time of year. This is because they can be particularly sluggish as they emerge from brumation, and if they are approached by a person or animal and unable to escape quickly enough, they may resort to biting. This can be avoided, however, if we don’t try to approach or handle them.

Male adders are grey or silver along their sides, unlike females which are brown (Photo: Matt Wilson).

 

The Road to Success? Experts share research at our Wildlife Road Mortality Conference.

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The Road to Success? Experts map route to try and safeguard wildlife in the future (written by Jules Robinson). 

The UK’s planned transformative infrastructure developments must not be at the expense of the countries wildlife, concluded experts at Froglife’s Widlife Road Mortality Webinar. Wildlife conservationists from around the world came together online at 1pm on 10th March 2021 to discuss their work in relation to mitigating the death of wildlife on our roads.

Froglife’s CEO, Kathy Wormald, introduced the webinar by sharing the work of Froglife over the past 30 years, particularly with regards to Froglife’s ‘Toads on Roads Campaign’ where thousands of volunteers take part each year to help toads and frogs successfully navigate roads on the way back to their spawning ponds to breed. Froglife is also currently running a Wildlife Tunnel Campaign, having undertaken research at a number of highway crossings for smaller wildlife including toads, demonstrating that for relatively small costs, tunnels and grids can be included in road schemes which provide a safe crossing for many other species.  Common Toad populations have declined by an estimated 68% in the last 30 years, and roads are a key factor. Research has also recently shown that in addition to the death of the adults, going to spawn, a few months later there are thousands of small toadlets, migrating from their spawning ponds into the countryside which are killed and not seen. The creation of balancing ponds and drainage ditches next to roads only exacerbates the situation.

Did you know that 1/5 of the Earth’s terrestrial surface is located within 1km of roads and that up to 100million animals die on roads around the world each year?  Badgers and pheasants top the list for the most common mammal and bird species in the UK, according to figures provided by Dr Sarah Perkins, co-ordinator of Project Splatter, a citizen-science monitoring scheme for wildlife vehicle collisions across the UK. Their research has also shown that 95% of the public are interacting with wildlife more by seeing it dead on the roads, than seeing it alive in the wild.

Citizen science proved to be a strong theme throughout. Debobroto Sircar (aka Debo), Head of Species Recovery and Wildlife Crime Control Division, Wildlife Trust of India spoke of the successful launch of RoadWatch, a user-friendly smartphone app that they’ve encouraged members of the public to use, which gathers necessary data such as photographic records, GPS location, type of animal, date of record etc. The app can transmit the data in less than a minute, with minimal effort and has helped them successfully map roadkill hotspots, identifying India’s most affected species so they can instigate mitigation measures, including signs, fencing and road closures at different times of the year. Their ‘#I brake for wildlife’ social media and car sticker campaign has also created awareness and is gradually reducing the incidence of wildlife road kills across the country and signs put up at rail crossings notifying train drivers of elephant corridor areas has also had a huge effect in reducing speed and the number of elephants being hit.

Dr Sean Boyle, a postdoctoral researcher at the Memorial University of Newfoundland, also recognised the importance of engagement and outreach activities, particularly involving youth, and he too mentioned a range of mitigation measures including the closure of roads such as one in Ontario for salamanders to make their yearly migration. He also spoke of recognising road mortality, as not just the roadkill itself seen on the surface of a road, but the ‘Road Effect Zone’ which is the area surrounding the road that an animal won’t approach or go near because of a combination of factors including pollution, light or sound and the fragmentation of habitat. His research has indicated this can be between 2-5km for some species. He also reminded us that we should include the effects of railways on wildlife mortality and the area around the tracks. Following on from his surveys into reducing the harmful impacts of roads and evaluation on the success of fences and crossing structures, he summarised that to best avoid wildlife road mortality humans need to modify their behaviour. Whilst he recommended the use of signage and putting up fencing directing wildlife to tunnels, he also recognised that people who regularly use the same route, initially reacted to the road awareness signs but then became less receptive as they got used to them.  Tunnels are costly and mitigation should be thought of at the time of construction.

Fragmentation was a key concern of both Froglife’s Reptile Project Officer, Ben Harris and author and ecologist Hugh Warwick. Ben spoke of the lack of desperately needed reptile road mortality research in the UK but that European data has indicated that despite the noise and ground vibrations from traffic, reptiles are still susceptible to road collisions, especially on smaller roads when adjacent to their preferred habitat and they may be attracted to the warm tarmac to bask. In the UK adders exist in small numbers so even if 1 or 2 are killed this could lead to a genetic imbalance. He suggested that we may need to adapt and install tunnels that reptiles will use it like the ‘Herpetoduct’ in the Netherlands, to reduce reptile road mortality and help stop fragmentation.

Hugh Warwick, a spokesperson for the British Hedgehog Protection Society, continued with this theme – as he told us that habitat fragmentation is one of the most serious threats to face hedgehogs. Whilst 167-335,000 hedgehogs were killed on the roads in a study undertaken in 2004, the current road kill estimate is 100,000 a year because of the hedgehog populations overall decline. He told us that with a starting population of 32 hedgehogs they would need 90km of unrestricted landscape not fragmented by fences, roads, lakes or ditches (created alongside roads to stop flooding, which can act as pitfalls). He called for all new infrastructure to have eco-ducts built in such as in the Netherlands, the A556 near Knutsford in the UK or the tunnels built over the A3 near Hindhead. “We need to start making our case for the value of nature and how life-giving it is”, he summarised at the end of his presentation which was the final talk.

Professor Roger Downie, Froglife Trustee who hosted the event agreed, “A big message coming loud and clear from to-day’s timely Froglife webinar on ‘Wildlife Mortality on Roads’ was that the UK’s planned transformative infrastructure developments must not be at the expense of the country’s wildlife. Wildlife needs safe routes to travel through our landscapes, and these must be built into all developments.”

Kathy Wormald, Froglife CEO concluded by saying, “We are extremely pleased with how the webinar went today, it has certainly raised the bar for action to be taken to stop the carnage of wildlife death on the worlds roads. Let’s collectively take positive action to bring this matter to a halt.  We know that it is impacting on the sustainability of wildlife across the globe resulting in population declines and in some instances extinction.  Governments need to take this matter seriously and help conservationists to address this issue.”

You can watch a recording of the webinar here: www.froglife.org/webinars

To sign Froglife’s Wildlife Tunnel Campaign please click here. 

The effect of the climate crisis on UK reptile populations

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Back in 2018 we discussed some of the impacts of climate change on amphibians worldwide (Froglife 2018). Since then, climate change has continued to accelerate, with global average temperatures in 2020 more than 1oC warmer relative to pre-industrial levels. The 2015 Paris Agreement has not, so far, caused nations to reduce their emissions anywhere near fast enough (Global Carbon Project 2020). The extent of future warming is projected to reach somewhere between 2 – 4oC or above, dependent upon a range of scenarios (IPCC 2014). The magnitude and speed of this change is unprecedented, and the impacts upon wildlife are already being seen.
We know that wildlife and their habitats – collectively termed the ‘biosphere’ – are in a fine, dynamic and interconnected balance. Unpicking the exact drivers of population changes is not straightforward, because they themselves are interacting in complex ways. What’s clear is that climate change is an additional stress factor for wildlife worldwide, on top of (and often accelerating) habitat loss and fragmentation, pollution and the impact of invasive species. In the UK climate change is predicted to cause hotter, drier summers and warmer, wetter winters. There will be greater extremes of weather, as well as sea level rise (Met Office 2019).


So how might the UK’s terrestrial reptiles be affected by climate change?
To begin to answer this, we can consider the direct effects of climate change on reptile physiology and behaviour, and indirect impacts from changing trophic interactions (populations of predators and prey), and from changes to reptile habitats (Le Galliard et al. 2012).


UK reptiles are more or less at the northernmost edge of the range for their species, although the adder, common lizard and slow worm have Scandinavian populations at higher latitudes. These three species are viviparous, meaning embryos develop within the body of the adult and born live. The smooth snake is ovoviviparous, which can be described as a more primitive form of viviparity, where the eggs develop within the mothers body. Sand lizards and grass snake are oviparous, meaning they lay their eggs externally, and embryos are therefore more reliant on environmental factors for their development. 

All UK reptiles however, have cousins residing in the warmer southerly climes of Iberia and Central Europe and the Balkans. So, we could assume that warmer climate here will improve survival in existing reptile populations, while enabling a northward shift of their distributions. Unfortunately, the reality is not that simple. Dunford and Berry (2012) modelled UK reptile population changes under low and high emissions scenarios for 2050 and 2080. Grass snakes appeared to be the only species consistently predicted to shift northward while maintaining the majority of their present distribution (see Cathrine, 2014 for tantalising evidence of Scottish grass snake populations), while slow worms showed a mixed northward shift with a contraction of southern populations. For all other species modelling predicted widespread population decline, greater under a higher emissions scenario (Dunford and Berry 2012).

Being ectothermic, reptiles are highly sensitive to their environment, with a tight bell curve describing their optimal climatic conditions (Le Galliard et al. 2012). Temperature and rainfall strongly influence reptile behaviour, and a changing climate has great potential to create mismatches – for example if temperature and rainfall is suboptimal either for reptiles or their prey species, especially at key points in the year such as hibernation emergence. Climate change is already affecting reptile prey populations and will continue to do so. For example Ewald et al. (2015) identified numerous invertebrate groups demonstrating sensitivity to extreme climate events over the last four decades. These trends must be considered alongside the ongoing impact of other pressures, particularly pesticide use (van Klink et al. 2020), all of which creates a complex picture. Climate impacts will vary between species groups and depend upon other biogeographical factors, meaning that impacts will not be the same everywhere for a given species.

In the UK, warming should increase reptile growth and maturation rates, due to longer periods of activity. Milder winters will likely reduce hibernation lengths for our reptiles. Earlier spring emergence, and activity extending further into the autumn and winter months would likely bring reproduction forward in the year, as gestation and incubation length is generally shorter in warmer climates. Larger body sizes in warmer climates may result in greater reproductive success (Le Galliard et al. 2012). Warm temperatures also enable a greater number of number of broods per year, observed in slow worms (Smith 1990), and common lizards (Bestion et al. 2015). However, life cycle changes may have additional impacts on population demographics and survival. Bestion et al. (2015) created experimental common lizard populations in climate-controlled chambers, with populations either subject to current average temperatures or those matching IPCC predictions for the coming century. Warming increased growth rates, brought reproduction forward, and resulted in a higher number of broods per season. However, this life cycle acceleration was coupled with a reduction in adult survival rates. Of several possible causes, the authors proposed the most likely to be greater metabolic requirements for larger individuals, with warmer temperatures increasing energetic requirements which could not be met fully by increased foraging, particularly when warm weather restricted their activity.


Our fragmented UK landscape creates major barriers for all wildlife. Reptile species are generally philopatric (tending to return to or remain near the same particular area), and so are especially sensitive to habitat loss, with populations often centred around relatively small habitat pockets or managed reserves. So even if a warmer climate could result in populations expanding northward, whether this will occur in reality depends on whether there are routes and habitats for them to do so. Araujo et al. (2006) simulated climate change driven UK reptile population dynamics under assumptions of unlimited and zero dispersal ability. Unlimited dispersal resulted in population expansion, with some local extinctions in southerly locations. Zero dispersal resulted in population contractions for all UK species, indicating climate change driven population collapse. This demonstrates the importance of considering all factors influencing population viability and dispersal in combination with climate change pressures.

Adders are usually reliant on specific habitat patches and are highly sensitive to habitat destruction and hibernation area disturbance due to their low recolonization abilities, even relative to other reptile species. On a local level, given typically small population sizes and low mobility, climate change driven habitat quality declines could result in local extinctions particularly as they may not have suitable adjacent habitat, nor the inclination to move (Gleed-Owen and Langham 2012). Although McInerny (2018) indicates that implementing appropriate mitigation can enable adder populations to persist alongside human modifications to local habitats, the adders ongoing decline nationwide is concerning (Baker et al. 2002, Gardner et al. 2019), which even a low emissions climate change scenario is likely to exacerbate (Dunford and Berry 2012).

adder


The dual pressures of habitat loss and climate change are even more apparent for our two most limited reptiles, the sand lizard and the smooth snake. Sand lizards can be found on lowland heath as well as coastal sand dunes. Smooth snakes are only known to be present on lowland heath in the south of England. Populations are generally isolated with little capacity for dispersal, creating a barrier to adaptation to changing conditions. Climate change could threaten habitat quality, for example increased frequency of heavy rainfall events could destroy sand lizard nests and reduce juvenile survival rates (Edgar and Bird 2006), while increased fire prevalence and sea level rise could destroy important habitat features. Dunford and Berry (2012) paint a particularly dire picture for the sand lizard, as its reliance upon highly specific landscape features such as south facing slopes and complex habitat mosaics makes the species highly sensitive to habitat loss. A small population of sand lizards has persisted on the Scottish Isle of Coll, since their introduction for research in the 1970s. Comparing the climate change resilience of this northern and relatively isolated population with that of other UK populations will be an interesting topic for study over the next few decades.

Heathland habitats are one of our most heavily impacted by urbanisation in the UK. Although direct loss through land-use change is now controlled by planning and environmental legislation, development in surrounding areas continues to increase pressure on remaining isolated heathland patches, through increased fire risk, predation by domestic animals and disturbance (Hayhow et al. 2019). Fagundez (2013) describes further pressures facing heathlands under climate change, including fires, and shifts in vegetation composition. We are used to a static conservation model for our heaths. As climate change progresses, the ideal climatic conditions for heath will likely expand in Britain (Thomas et al. 1999), and Loidi et al. (2010) point out that extensive lowland heaths throughout southern Europe support a greater diversity of reptiles than we see here. However, whether habitats will be able to expand is an entirely human choice (Coll et al. 2016, Hayhow et al. 2019).

All of the pressures we have presented here are anthropogenic in origin, born from human choices, and our expectations of how we can and should manage the land and its resources. The enormity of shifting these practices cannot be underestimated, but at least it is within our abilities to do it!

Written by Zak Mather-Gratton 

References
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Baker, J., Suckling, J. and Carey, R., 2002. Status of the adder Vipera berus and the slow-worm Anguis fragilis in England. English Nature.

Bestion, E., Teyssier, A., Richard, M., Clobert, J. and Cote, J., 2015. Live fast, die young: experimental evidence of population extinction risk due to climate change. PLoS Biol, 13(10), p.e1002281.

Cathrine, C., 2014. Grass Snakes (Natrix natrix) in Scotland. Glasgow Naturalist, 26(Part 1), pp.36-40.

Coll, J., Bourke, D., Hodd, R.L., Skeffington, M.S., Gormally, M. and Sweeney, J., 2016. Projected climate change impacts on upland heaths in Ireland. Climate Research, 69(2), pp.177-191.

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van Klink, R., Bowler, D.E., Gongalsky, K.B., Swengel, A.B., Gentile, A. and Chase, J.M., 2020. Meta-analysis reveals declines in terrestrial but increases in freshwater insect abundances. Science, 368(6489), pp.417-420.

Le Galliard, J.F., Massot, M., Baron, J.P. and Clobert, J., 2012. Ecological effects of climate change on European reptiles. Wildlife conservation in a changing climate, pp.179-203.

Loidi, J., Biurrun, I., Campos, J.A., García‐Mijangos, I. and Herrera, M., 2010. A biogeographical analysis of the European Atlantic lowland heathlands. Journal of Vegetation Science, 21(5), pp.832-842.

McInerny, C.J., 2019. The study and conservation of adders in Scotland. The Glasgow Naturalist Volume 27, p.67.

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