The Common or Viviparous (live-bearing) Lizard Zootoca vivipara averages 12 cm in length, of which more than half is the tail. Lizards that have shed their tails as a response to predation are quite frequent and the tail may be absent or partially re-grown. It has very variable colours, mainly mid-brown with darker and lighter stripes. There are many colour variations, including strongly striped animals and quite dark-coloured individuals. Some males are yellowish or sufficiently green that they look like Sand Lizards. Young animals are plainer, dark grey or almost black. There are no consistent differences between the sexes on the upper side. The underside of the males is yellow or orange, with dark spots, brighter than the females, which are off-white, lemon or grey underneath with few or no spots (Beebee and Griffiths, 2000). There are echoes here of the sexual differences in the underside of Smooth Newts Lissotriton vulgaris. Inexperienced observers occasionally report picking up a lizard or several lizards by hand, but these are almost always just terrestrial newts.
They feed on a broad range of small invertebrates, alternating between basking in a favourite spot and hunting for prey. Log piles, dry stone walls and stone ruins are favourite basking spots. Dark-coloured substrates warm up more quickly in sunlight, so basking lizards are more likely to be seen on dark backgrounds in full sun. Hibernation may take place in the same locations, under log piles, in the footings of dry stone walls or in small mammal burrows.
Common Lizards emerge from hibernation as the weather warms up in April. Males moult after a few days of feeding and develop their brighter breeding colours. Mating takes place in late April/ early May, with females often mating with more than one male. Development of the embryos takes about three months, depending upon summer temperatures and the condition of the female. Pregnant females maintain a higher temperature to promote the growth of their young by basking more than other adults. An average of seven or eight young are in each brood. Technically, they are ovo-viviparous, as the young are born in a transparent membrane, from which they break out in a day or so. On emergence, the four cm long young lizards can immediately feed and look after themselves. If they have been born early enough to feed and build up reserves before hibernation, they reach seven or eight cm by the autumn. At the end of their second summer they are 10-11 cm long. Like most of our amphibians and reptiles, the males are sexually mature earlier than the females. Males can breed two years after they have been born, females three (Beebee and Griffiths, 2000).
Common Lizards have many predators, particularly Kestrels Falco tinnunculus and Buzzards Buteo buteo, Stoats Mustela erminea, Weasels Mustela nivalis and Hedgehogs Erinaceus europaeus. Adders Vipera berus, which are often found in the same locations, are also regular predators. The newborn young are particularly vulnerable, and mortality in the first year can be over 90%. After the first year life is safer and Common Lizards live to an average of five or six years.
Common Lizards need insect-rich habitats with open spaces for basking, cover for protection from predators and suitable hibernation sites. Their main habitat in our region is the moorland edge, where there is varied topography including rocky stream banks, disused quarries and dry stone walls. The higher heather moors are also occupied, except for the larger bogs and mires, which lack hibernation sites. A mix of wet and dry moor provides both rich insect prey and hibernation sites. As with the other reptile species, the burning of heather moors for the management of grouse is very detrimental. Some of the fragmented moors on the edges of the main Pennine area that are not managed for grouse are better for reptiles than the main moor.
The moorlands in the area south of the Derwent Reservoir and north of Tunstall Reservoir, bounded by the A68 road, provide one of the best areas of reptile habitat in the region. This area, called the “Heart of Durham” by the Durham Wildlife Trust, has low moorlands, small woodlands, disused quarries, disused railway lines and small stream valleys that seem to provide just the right mix of well-connected reptile habitat. There are similarly suitable, more localised areas at Kielder and Redesdale Forests, Fontburn and at Kyloe Hills in Northumberland and at Scaling Dam and Eston Moor on the edge of the North York Moors National Park (Durkin, 2012B).
At lower altitudes, lizards can be found in areas that provide the same mix of basking, feeding and hibernation features. These can be disused quarries, disused railway lines, stream valleys and open woodland. The main problem for lizards in these mid-county areas is that such habitats are mostly fragmented and isolated, so re-colonisation events are much rarer than local extinctions. There has been a considerable decline in the lowland distribution of Common Lizards in the North East.
The handful of places with remaining populations in these areas are mainly centred on disused railway lines and disused quarries. The Ashington/Linton area of Northumberland and the magnesian limestone quarries of County Durham are the main examples, though there may be others that have yet to be detected. Darlington, with its strong network of disused railway lines, is the only example of an urban population, though building developments in recent years have removed much of this habitat and fragmented what remains.
The coast, however, provides long stretches of continuous suitable habitat, with sand dunes, sea cliffs and coastal denes. Though this is interrupted by the Tyne, Wear and Tees conurbations, and also by the tidal rivers, the intervening stretches of suitable habitat remain intact and viable. Northumberland may have coastal populations from Seaton Sluice dunes to the Scottish Border, but is poorly recorded. There are no records from Lindisfarne, though there is suitable habitat there. There is a population in South Tyneside, where Lizards Farm still has lizards, and another between Hawthorn and Castle Eden Dene mouths. Suitable habitat continues southwards along the coast, where there are known populations between Crimdon Dene mouth and Hartlepool Headland. South of the Tees, there are populations at South Gare dunes and around Saltburn.
At Teesmouth, north of the river, the coastal population seems to extend into some of the large industrial areas, where there is a lot of suitable habitat behind security fences, undisturbed by walkers and dogs. Records from this area are all since 2005 and are increasing. There is some doubt as to whether this is natural colonisation or a possible deliberate introduction.
Lizards have been marked by one cluster of place names in the North East, at Lizards Farm and Lizard Lane on Cleadon Hills, and Lizard Point on the adjacent coast, where Common Lizards can still be found.
Just over half of our Common Lizard sightings that are on record are from casual encounters. Intentional surveyors use a combination of keen observation and quiet approach, trying to spot lizards basking on suitable rocks without disturbing them. Binoculars help the observer to see them from a distance. Sheets of corrugated iron or felt roofing material (called “tins”) can be placed at strategic, sunny spots, to encourage animals to come out into the open to bask on these tins at points where they can be seen from a safe distance. The surveys are usually done at a time of day when the lizards are just warming up and before other people can cause disturbance (Gent and Gibson, 1998).
Common Lizards are often found in the same upland habitats and locations as Adders and Slow Worms Anguis fragilis, and in the same coastal habitats as Slow Worms. Adders can be an important predator of Common Lizards. In the mid county lowland areas Common Lizards are usually the only reptile species present.
by John Durkin