Sand Lizard

Each spring, male sand lizards turn bright green along their flanks, brightest in April and May, then fade by late summer. The colour attracts females and warns rivals, and in one study the brightest males did best in competing for nesting sites. Females stay brown or grey for camouflage. Males become highly aggressive a few weeks after leaving hibernation, because the mating season lasts only about 17 days a year. Mating itself takes just 2 to 4 minutes, but a male then guards the female for hours or even several days, which can use up to 18 percent of the season. A male mates with at most six females in a season. It is a short, tense race, and only the boldest and brightest get to finish it. Timing matters in so short a season.

When a predator grabs a sand lizard, the tail can break off and keep wriggling while the lizard escapes. This is called autotomy. Lizards able to drop their tails run faster and get away more often. In one study, about 63 percent of adult males and 59 percent of adult females had lost a tail, and researchers recorded 180 loss events in a single season. The trade-off is lasting, because a regrown tail never reaches 80 percent of its original length. Escape through tail loss was estimated to raise survival by only about 5 percent, so it is a helpful trick, not a guarantee. Some animals even lose the tail twice. Nine in that study did. A sand lizard that keeps its tail has usually simply had luck, or speed, on its side.

A sand lizard eats insects and spiders, including grasshoppers, beetles and caterpillars, and because it is cold-blooded it needs little food for the energy it uses. Yet the hunter is hunted all season. Kestrels, buzzards, falcons, shrikes, crows, pheasants, foxes, badgers, weasels, smooth snakes and domestic cats all take sand lizards. A study at one site found that females carrying eggs often failed to escape predators, with estimated survival of under 1 percent during the early active season, compared with about 29 percent later on. Egg-laying is the most dangerous part of the year. Adult length is only about 20 cm (8 in) including the tail, so almost every bird and mammal nearby can handle it. Dense cover and burrows are its best defence against so many enemies. Staying hidden is a daily job.

Sand lizards dig their own shelters. Their burrows can reach 1 m (3.3 ft) deep but stay narrow, with a hidden entrance that bends sharply after a few centimetres (about 1 to 2 in). Some lizards even dig winter burrows into the walls of rabbit warrens. They use burrows for sleeping at night and for hibernating through winter. Males usually start hibernating in late August or early September, and females follow about a month later, in September or early October. Hatchlings dig in during October. The lizards emerge again in April and May, and adults are usually seen between April and October. Released young lizards may also shelter in small mammal burrows. Winter shelter is vital. Sandy, sunny ground matters all year, because it gives them somewhere to dig, to bask and to rest safely.

In June, a female digs an egg burrow in open, bare ground, then lays 6 to 12 eggs in the wild and buries them in warm sand. Captive females have laid up to 18. The sun heats the ground, and that warmth, not the mother, incubates the eggs. Wild eggs usually hatch after 2 to 3 months, in late August or early September, while artificially incubated eggs can hatch within about six weeks. The sand lizard is the only native British lizard that lays eggs, since common lizards and slow worms give birth to live young. Larger clutches tend to produce smaller hatchlings, and early clutches tend to produce larger, more successful young. In Great Britain, the species survives mainly where coastal sand allows incubation. That makes sand essential for every new generation.

In Britain, the sand lizard has lost most of its home. Losses of suitable habitat in the remaining native areas are given as about 97 percent in Merseyside, 95 percent in Surrey and 90 percent in Dorset. A captive breeding programme now runs at ten centres, and Marwell Zoo, a partner since 1989, helped re-establish 26 populations on heathland and coastal dunes in southern England. Young lizards are released in early September, so they can settle in before hibernating in October. More than 10,000 have been released in England and Wales. The species is strictly protected by law, and the plan has three parts: protect existing sites, manage them well, and reintroduce lizards to places where they once lived. Juveniles are reared outdoors until release, in cohorts of 80 per year over three years.