Adders in the forest
An adder crossing a track in the forest
Adders in Rockingham Forest
by Alan Butler, County Recorder and Kevin Clarke
Chair and Vice Chair of Northants Amphibian and Reptile Group (N-ARG)
All photos on this webpage are copyright Alan
Butler and Kevin Clarke
Adders have been sparsely distributed in the midlands for more than a hundred years. For instance, in Gerald Rowley Leighton’s book of 1901, entitled “The Life History of British Serpents and Their Distribution in the Isles”, he stated that adders were even then scarce in Northamptonshire, but used to be common at Brampton Wood near Desborough. He went on to say that the keeper there often used to kill adders and none had been seen for the past six years. He added that J. A. Vipan of Stibbington Hall, Wansford mentioned that adders were plentiful in a nearby large wood in North Northamptonshire, and was still found there but in much reduced numbers.
The former continuous area of the ancient hunting forest of Rockingham, has today been reduced to much smaller and isolated woodlands. This has resulted in the loss of many of the very special and in some cases rare animals that once lived there. In the latter half of the 20th century the decline of adders across the country became of significant concern and in 1983 the Nature Conservancy Council recorded declines in 3 out of 12 regions of the UK. This trend continued and a follow up survey in 1991 found that adders were declining in half of those 12 regions! About 20 years ago another study revealed that the most significant decline in adder numbers was in the Midlands. In 2005 ARG (Amphibian and Reptile Groups) carried out a nationwide survey named “Make the Adder Count”. Experienced fieldworkers recorded numbers of adders emerging from their hibernacula in the spring over a period of more than 10 years. The results of the survey were published in 2019 and revealed that 90% of adder populations were in serious decline and that the number of sites supporting adders could be reduced to just a handful within 10-20 years!
Adult adder basking. The contrasting almost black zig-zag pattern on a pale background and the slender, gently tapering tail indicates that this is a male. Notice also the well-defined lateral spotting which is typical of males.
Another adder basking. The relatively thicker body with somewhat subdued brown markings and poorly defined lateral spotting are characteristic of adult female snakes. Also, whilst not visible here, relative to males the females have a shorter tail, tapering quickly beyond the vent.
Across the UK 90% of adder populations are thought to be in decline
Current status in Northamptonshire
Today our records indicate that in the Rockingham Forest area there are perhaps just two stable adder colonies present, one large and one smaller population, with smaller isolated populations in around five other sites spread over an area of about 90 square kilometres. The origin of these satellite populations isn’t known; they may be the isolated remnants of former larger populations or some may be attempts at recolonization from the stronger populations.
To evaluate the health of a snake colony two methods of surveying are used throught the season. Visual surveying is an excellent way of locating snakes and provides a great opportunity to cover larger areas and new ground, but it requires a good deal of patience and experience to acquire the required skills to be successful. It is however key to determining the distribution of animals on a site.
Another equally valuable survey method is surveying using "refugia", often lightweight corrugated roofing sheets or corrugated steel sheets. Several refugia are laid out in areas where adders are thought to occur and checking them regularly provides systematic data to indicate the health of the population.
Both techniques can also help to identify "hibernacula", where snakes spend the winter. They also provide information about the movement of snakes during the season, evidence of successful breeding and, very importantly, the dynamics of the population – is it stable, expanding or in decline? In the past five years N-ARG volunteers have undertaken more than 300 reptile and amphibian surveys with half of these being in 2022.
150 surveys from 2018-2021 ...
and then 150 more in 2022
Within Rockingham Forest we know there are two main adder populations. In the larger of the two, there may even be evidence of increasing numbers, especially into those areas where new habitat has been created. It is quite certain that snakes (and other reptiles) have colonised these new areas, but given the increased level of N-ARG activity in the past two years, the increased number of adder sightings might just be due to increased numbers of surveys. The smaller colony appears to be healthy, but given the size of this population there some are concerns about its viability. We fear that some snakes in one of the hibernacula may have drowned during winter flooding and with small populations there is always a concern about viability for a number of reasons including genetic isolation. However, conservation efforts made here by the local community, have been impressive, and with the creation of new hibernacula and improvement and expansion of suitable habitat generally, we hope that this population will have a healthy future.
The story regarding the satellite populations is a different matter. Some of these have declined significantly or even appear to have been lost, but it is possible these were only transitory locations anyway. In some areas populations are still present and one in particular appears to be healthy with evidence of breeding taking place.
In Rockingham Forest the two main populations seem stable and healthy
A juvenile adder where the cryptic camouflage provides a high degree of protection from aerial predators- look carefully for the zig-zag in the centre of the image
Adder distribution across the large of the two Rockingham Forest sites as recorded in 2020 and 2022. There is evidence that this population may be increasing, probably as a result of conservation work undertaken, but the increase in number of records is in part a reflection of the significant increase in survey effort.
Today, Northants-ARG, working in partnership with landowners, local communities and other bodies, undertake conservation work to improve existing habitats and, where appropriate, to create new habitats. This work is based largely on providing the animals with good basking opportunities whilst also ensuring adequate protection from predation. Other work includes identifying hibernation areas for protection, especially from other necessary land management work.
Traditional forestry management methods utilised pollarding and coppicing, but were replaced in the 20th century by larger-scale economic harvesting of valuable timber and replacement with rapidly growing coniferous species. These can quickly close the canopy resulting in rides with little sunlight.
More recently the adder was identified as a species of concern under the “Back from the Brink” project managed by Butterfly Conservation. This project was the driving force to create suitable and improved habitat for butterflies. Large-scale widening of forest rides and scalloping of narrow ones was carried out, allowing more light to penetrate and encourage nectar-rich plant species for butterflies. This was very beneficial for snakes too and in addition some large areas of dense woodland were extensively cleared to create open glades with the brash stacked to create "windrows" along east-westerly lines. These clearings are away from the main rides and consequently are less prone to disturbance, particularly from dog walkers, benefitting snakes and dogs alike. These windrows, carefully stacked up to 2 meters high, create good hibernacula for over-wintering snakes with protection from flooding and sub-zero temperatures that can prove fatal during the winter months. They also offer excellent summer refuge for adders, with protection from aerial predators and microclimates sheltered from the wind for basking and mating.
Natural hibernation sites are very important and these can be supplemented with creation of both “natural” and artificial hibernacula. Natural hibernacula can be created by leaving storm-felled trees in situ, complete with large root balls, or by stacking felled timber into log piles. Artificial hibernacula have been created by making shallow scrapes and stacking cut timber to a height of 2 meters or so. Ensuring good drainage in such structures is of paramount importance.
Other hibernacula have been created by stacking clay drainage pipes and covering with soil to provide access deep into the structure whilst providing good frost protection and drainage. In areas of Rockingham Forest there has been a long tradition of quarrying and over the years piles of scrap stone have been dumped along quarry boundaries and dry-stone walls have been created to delineate field boundaries. These structures provide excellent hibernation and summer refuge sites for adders and, particularly where accompanied with hedging, can provide excellent wildlife corridors which are so important to encourage snakes to disperse and colonize new areas.
Typical woodland habitat for adders in parts of Rockingham Forest. Notice the broad sunny ride.
Newly created area for reptiles in Forestry England woodland. The windrows can be seen crossing the cleared area
A natural hibernaculum
- a storm-felled tree with exposed roots
A natural hibernaculum - a pile of rocks
A man-made hibernaculum
- rocky debris piled over drainage pipes
A natural hibernaculum - a hole beneath a tree
A man-made hibernaculum - a pile of timber and brash
Engaging with people
Working with Butterfly Conservation, N-ARG have held joint public engagement days which have proved to be very popular, providing a platform to promote the plight of the adder which, whilst protected under the Wildlife and Countryside Act of 1981, is still persecuted to some extent today.
For example, last year we had reports of 4 adder fatalities of which at least 2 are believed to have been due to deliberate human action. Public engagement events are great fun and include activities specifically design to interest younger people, including nature walks to showcase some of our flora and fauna in their natural surroundings.
In 2022 a day for land owners and managers was held at Laxton Village Hall to discuss key practical conservation measures that can be taken for adders in particular. A key element of the meeting was to encourage networking between stakeholders. It was a great success, opening up lots of opportunities for habitat creation or improvement. The enthusiasm amongst the 30 or more delegates was really impressive and as a result N-ARG will be setting up surveys in at least three new locations in the coming season., Two of these are in the Rockingham Forest area where adders have been sighted.
Remains of a female adder apparently bludgeoned to death. Unfortunately this was a gravid female that had been observed mating earlier that spring. This snake was found near a lay-by on a major trunk road.
How to observe adders
Observing adders in the field can be very challenging but also very satisfying. However, it should be restricted to observation from a good distance to ensure the adders have the privacy they need and are not disturbed. Using binoculars is an excellent way to achieve this. Adders are venomous animals, but are also shy and non-aggressive. Bites to humans are rare in this country and those that occur are usually the result of someone getting too close or provoking the adders. Dogs are at higher risk of being bitten, probably as a result of their often-inquisitive nature combined with their speed of engagement. Under the statutory Countryside Code dogs should be kept under effective control and kept away from wildlife. The majority of dog walkers do just this and in practice adder bites to dogs are quite rare and most that are bitten do survive.
From about the middle to the end of October, depending on the season, adders enter their chosen hibernaculum for the duration of the winter. They frequently hibernate collectively and a single hibernaculum may house many individuals. The males emerge approximately 2 or 3 weeks before the females and this can be from late February to early March, depending on the weather. Males will emerge on sunny days and spend many hours basking in the full sunshine to raise their body temperature to develop their sperm. At this time of the year, before the foliage has become too invasive and particularly at times when the ambient temperature is not too high, the snakes will be somewhat torpid and easy to observe. For this reason this is also the time of year when dogs may be at higher risk of being bitten.
Adders are venomous but are also shy and non-aggressive
Visual surveying from a distance reveals a male adder basking in the grass at the base of a hedgerow. Spotting adders can be difficult and is best achieved with a slow and cautious approach with a pair of binoculars.
When the females emerge a few weeks later, the males will be waiting in anticipation of mating with a female or two. Both sexes are relatively easy to observe at this time. The males may be pre-occupied charming a female, or sparring and chasing away any rival male that approaches too close. Mature males take part in a sort of combat ritual during which each tries to rise up above the other. This ritual is often referred to as “the dance of the adders” and is a magnificent sight. Once engaged the snakes may be oblivious to events around them, offering you an excellent opportunity to witness the whole affair including, with luck, the copulation of the dominant male and his female.
After mating, the males (including those unlucky enough not to have mated) disperse and during the summer can be difficult to locate. They spend much of their time tucked away deep in the foliage or down a rodent burrow. The females however, and in particular the gravid ones, continue to bask in the sun to develop their young. As the average temperatures rise during the summer they no longer need to bask for prolonged periods and during higher temperatures they move to cooler areas to avoid overheating. They also tend to bask amongst the foliage, known as mosaic basking, taking advantage of their cryptic camouflage to avoid predation. Gravid females in particular often stay loyal to their favoured basking areas, moving just a few metres away before returning.
Females typically give birth to between 6 and 20 live young in late summer. The young are very small and pretty, being a brick red colour with contrasting patterning. They are born ready and equipped to deal with life, including the ability to hunt and envenomate their prey. As pretty and small as they are, like adult snakes they should never be picked up or handled.
As part of the monitoring process "refugia" are often used for part of the surveying. Occasionally you may find these while walking in the area but they should not be tampered with and only lifted by those trained to do so. Adders may sometimes be in close proximity to the refugium, but may not be seen by the casual observer. They may also be under the refugium itself close to the edge, which could pose a risk of your being bitten if you lift a refugium.
Well hidden female adder "mosaic basking"
Tiny neonate adder - compare the size of the fly just above it. Adders are born live in the amniotic sac which can be seen to the right of the picture
How to help
If you should notice any reptiles or amphibians, we are always keen to know about your sightings. Ideally records should include a photo of the animal (taken from a safe distance), the location (ideally a grid reference) and the date. If the gender and stage (new born, juvenile, adult) is known this is also good information. The records can be logged using recordpool or by emailing or texting (see below for details).
We are always looking for volunteers to help with our surveying of all herpetofauna. (reptiles and amphibians). Currently we have sites the length of the county so it is likely there may be an opportunity to get involved reasonably close to home, and training can be provided. Please get in touch if you are at all interested.
A male adder hunting
We acknowledge the work of all the volunteers who have given their time freely, and also the support of land owners, managers and teams who have helped with conservation work. Thank you to everyone who has helped in any way to promote the plight of adders in our area.
The season got off to a very early start in 2023 - see Kevin's blog article here: Rockingham Forest Adders in February!
About Alan Butler
A physicist by training, I have pursued a career in scientific research and development at various research centres, both in the UK and abroad, for most of my working life, but I developed my passion for reptiles and amphibians long before that. When my career took me into consultancy I found more time for the herps and when retirement finally caught up I was pleased to get more formally involved with Northants-ARG, having been a member of Surrey-ARG for many years. I am a keen amateur wildlife photographer focussed primarily on the herps but also the wider fauna and flora when the opportunity arises.
About Kevin Clarke
Kevin lives and works in Nottinghamshire and is the Chair of the Nottinghamshire Amphibian and Reptile Group. Adders do not occur in that county, so Kev spends much of his summer helping to monitor his favourite reptiles in Rockingham Forest. His uncanny ability to pick out adders hidden in thick vegetation has become legendary. If Kev can't see an adder then it almost certainly means there isn't one there!