Adder

Overall vulnerability

Feature assessed:

• Adder (Vipera berus)

Special qualities:

• Internationally important and locally distinctive wildlife and habitats

Feature description:

The adder is the UK’s only venomous snake. It is easily recognised by the distinctive dark zigzag pattern down its back. Found in open and mixed habitats such as grasslands, woodlands, and heathlands, adders occupy a limited range in the PDNP. Population estimates are difficult; but there remains a highly concentrated group of adders in the Eastern Moors area – now representing the stronghold for adders in the PDNP. In marked decline across the UK and northern Europe, every adder population is nationally and internationally important for the future survival of the species.

How vulnerable are adders?

Adders in the PDNP have been rated ‘high’ on our vulnerability scale. This score is due to high sensitivity and exposure to climate change variables, coupled with a poor and fragmented current condition, and a moderate adaptive capacity.

The PDNP adder population currently appears to be relatively stable despite its reduced and fragmented nature. Small adder populations are likely to be more vulnerable than larger, more stable populations. Adders have some scope for adapting to climate change, particularly if habitat management is continually improved. Translocation to new sites may also be an option for securing a larger population range within the PDNP.

Current condition:

The UK adder population and distribution has declined dramatically since the 1970s and 1980s. Continued decline has led to some experts predicting they could go nationally extinct at all but a few sites in the next few decades. The main population in the PDNP is in the Eastern Moors where the population, thought to number around 300, is currently stable or only in slight decline. Other adders in the PDNP are limited to single sightings where individuals or small populations are extremely vulnerable.

Public pressure and disturbance combined with habitat management and fragmentation are reported as the main drivers behind the marked decline in numbers. Historic land management such as burning, over-grazing, and predator control likely determined the current distribution of adder within the PDNP. Overgrazing is now considered low risk, but trampling of habitat by cattle is still an issue at some sites. Habitat fragmentation, inappropriate habitat management, and disturbance by people and dogs is still of concern. However, the main current risk factor is the destruction of habitat, especially by wildfire and erosion. Individuals may be killed by wildfire, inbreeding risks may increase, and populations may suffer due to increased exposure to predators and a loss of food sources. Erosion of peat and soils may create large bare patches that adder are unlikely to use as the peat can get too warm and lack the vegetation cover they need to hide.

Other risk factors for adders are predation and disease. Animals such as buzzards, pheasants and dogs are known predators of adders. While predation by these animals has been confirmed, there is no evidence that is a limiting factor for population sizes. Little is known about diseases affecting native reptiles but testing has confirmed instances of Snake Fungal Disease and salmonellosis in adders, though the level of risk to the species is currently unknown.

What are the potential impacts of climate change?

Overall potential impact rating

Direct impacts of climate change

As reptiles, adders are sensitive to changes in air and soil temperatures. During warmer winters and hotter summers, soil temperatures are expected to rise particularly in areas of bare ground that are exposed to more sunlight. Adders may benefit from the warmer climate in some areas, with improved growth rates, longer activity periods, and increased fecundity success. However, winter mortality rates may worsen if shorter hibernation periods are followed by cold snaps. Adders may be more vulnerable to extreme weather events or more at risk from human disturbance if they are active for more of the year. Data Certainty: Moderate

Changes to rainfall patterns could alter grassland and moorland habitats that adders rely on. As vegetation cover decreases in some areas and increases in others, the change in habitat structure could affect adders as well as their prey. Water and heat stress may negatively affect adders and their embryos. Other extremes such as flooding may drown some individuals but are less likely to have long-term effects. Data Certainty: Moderate

The growth rate of plants can be influenced by atmospheric composition and nutrient deposition. With a predicted rise in carbon dioxide, it is possible that increased vegetation cover will benefit adders. In areas with less vegetation management, they may gain extra protection from predators and disturbance. However, the benefits gained from this vegetation increase are limited, as adders still require some open spaces for basking. Data Certainty: Low

The climate space for a species can be estimated by modelling temperature and precipitation levels under different emissions scenarios, taking into account known species distributions. In both low and high emissions scenarios, modelling predicts that there will be huge losses of appropriate climate space for adders across the UK, especially in England. In the PDNP, climate space could increase under a low emissions scenario but it is likely to be lost or transient under a high emissions scenario. Data Certainty: Moderate

Other indirect climate change impacts

Wildfires are predicted to become more frequent with hotter, drier summers. The loss of large areas of moorland vegetation could be detrimental as moorland habitats provide cover for adders and their prey. The adder population may decrease as individuals and their prey are killed in fires. Given the relatively small extent of the PDNP left with adders present, the whole population could be at risk if wildfire is widespread. Data Certainty: Moderate

Human behaviour change

Adders are sensitive to disturbance, whether from passing visitors or land use changes. As tourist numbers in the PDNP are expected to increase on sunny days, basking adders are more likely to be disturbed by people and dogs as the numbers of these passing visitors increase.

Land use choices will also affect the extent of disturbance to adders within their habitats. In areas where grazing intensity decreases or management is reduced, adders may gain new habitat where they can thrive with lower levels of disturbance. Conversely, in areas with increased disturbance or dramatic habitat changes such as vegetation loss across a wide area, adders may lose some of their habitat and have an even more restricted range within the PDNP. Data Certainty: Moderate

Sedimentation or erosion

Vegetation cover is necessary for adders to hide. As extreme events such as flooding, landslides and drought become more common, some adder habitat could potentially be altered. Vegetation loss that leaves areas of ground exposed poses the biggest risk. Adders with less cover are more likely to be disturbed by humans and animals, are more vulnerable to predation, and may lose some of their foraging habitat. Populations may also be affected as some individuals are killed and there is increased fragmentation between existing groups. Data Certainty: Low

Invasive or other species interactions

Stressed animals are more susceptible to disease and predation. With warmer, wetter winters predicted, diseases such as Snake Fungal Disease may become more of an issue for adders. Other new snake diseases could also be introduced from Europe as the climate becomes more suitable. Predator numbers are likely to vary and some predators may gain an advantage if adder habitat is altered and adders are left with less cover. An increase in predation could negatively affect population size. Data Certainty: Low

What is the adaptive capacity of adders?

Overall adaptive capacity rating

Within the PDNP the adder has been confined to a small area of its previous range. Despite the highly fragmented population that remains, there is potentially viable habitat available further north. Within the PDNP, the main obstacles to their expansion are their small home range and the roads that separate habitats. However, population movement could be encouraged through translocation to other suitable sites. Structural diversity is a key habitat requirement that will enable adders to cope with thermal extremes. Data Certainty: High

Large population sites are vital for the future survival of the species. Adders are slow to recover from any losses of individuals, as they only reproduce every two to three years. Small populations are at a much greater risk of extinction from a single event such as flooding or wildfire. Where large areas of habitat are lost, it can be difficult for adders to recover if there is nowhere to disperse. Although adders are generalist species, a mix of plant species is needed to promote a diversity of prey species. A recent site survey has suggested that monoculture bracken may be a limiting factor and adders do better at sites that are more diverse. Data Certainty: Moderate

Adders are protected under the Wildlife and Countryside Act (1981), where killing, injury and trade are an offence. They are a biodiversity priority species under the Natural Environment and Rural Communities (NERC) Act 2006, which gives them further protection and encourages conservation action by relevant local authorities. The incorporation of habitat requirements into management plans is one way populations may be enhanced in the face of climate change. Data Certainty: High

Habitat management plays a significant role in the viability of adder populations. One study showed that appropriate management was a positive factor at more than 40% of UK adder sites. Management of adder habitat on the Eastern Moors is now carefully carried out to minimise disturbance. Burning has stopped completely and cutting is only done during hibernation. Continual management of PDNP adder sites is likely to help offset climate change stressors. Data Certainty: High

Funding opportunities may be available through Amphibian and Reptile Groups or Wildlife Trusts. Most work on adders is currently done by volunteers. Data Certainty: Moderate

Key adaptation recommendations for adders:

Improve current condition to increase resilience

The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations are aimed at improving the condition of the feature at present, therefore making it better able to withstand future changes to climate.

• Continue improving habitat condition: ensuring there are suitable sites for basking, hibernation, and breeding. This will help to make existing populations more resilient.
• Continue gathering sightings and creating photo database of individuals.
• Increase habitat connectivity: to aid dispersal and breeding.
• Investigate translocation to new sites. Further research is required.
• Encourage further uptake of environmental land management schemes by farmers within the PDNP.

Improve current condition to increase resilience: Targeted conservation efforts for important sites and at risk areas

The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations are conservation measures aimed at those sites that will have the biggest impact for this feature – either because they are particularly important for the feature or because they are most at risk from climate change.

• Limit disturbance at known sites (particularly at hibernaculum during winter).
• Develop fire contingency plans, and ensure management of habitats reduces fire risk e.g. rewetting and increasing species or structural diversity. Influence visitor and behaviour management plans and practices to minimise ignition risk.