In order to hide, to move about and to regulate their temperature they look for terrain provided with hedges, undergrowth, thickets, low walls, stacks of wood, stacks of stones, fissures, etc; which allow them to easily choose between shadow and sun, between underground and the surface, without being too exposed to danger. They also prefer less aesthetic hiding holes such as piles of broken bricks, tarpaulin or metal which are well exposed to the south. The vegetation must be varied, with both dense cover and small cleared open zones. Certain species, such as the grass snake, need ponds or wet zones in order to find their prey (frogs, etc.) but also piles of manure, compost or branches for their clutches of eggs. 

Why are they regressing?

This regression of populations has thus been confirmed by a study involving 24 years of the monitoring of a community of reptiles typical of northern Europe over a 19km stretch of railway: SNCB line 162, which links Namur to Luxemburg, in central-south Wallonia (2). Over the course of this study, Eric Graitson and his colleagues brought to light a steep regression of the populations of common European adders and, to a lesser extent, a regression in the populations of common wall lizards and grass snakes. On the other hand the populations of smooth snakes have strongly increased. The latter having probably colonised the habitats frequented by populations which are regressing through the effect of competition for the prey of the young and for sun exposure sites. This competition amongst species was probably caused by the climate changes which have taken place over the last two decades. ‘A railway line is a relatively stable milieu and yet two species out of six are undergoing regression, that’s a third of the species, it’s already a lot!’ states the researcher.

Besides climate changes, the main cause of the regression of populations is the loss or modifications of their habitats. Reptiles are in effect poor colonisers and thus do not often have the possibility of reaching habitats further away which could suit them. The populations thus become isolated from the others, even more threatened with extinction.

Thus the closing off of habitats due to the afforestation of agricultural zones, abandoned habitats such as the quarries or the grasslands undergoing agricultural land abandonment, heaths or the planting of spruces sentences a whole proportion of the territory which no longer offers any possibility of either thermoregulation or shelter.

The simplification of the milieus and the intensification of agricultural practices are other important causes of the loss of habitat for the reptiles. The conversion of certain grasslands into grasslands into cultivated land, close mowing alongside the hedges or grouping together land parcels into large scale farming zones reduce the refuge areas and do away with the connecting channels, such as hedges, between diverse habitats. The increase of livestock pressure on grasslands leads to a levelling of vegetation, a reduction of shelters and disturbs the lizards and the snakes.

(2) Synthèse de 24 années de suivi d’une communauté de reptiles typiques du nord de l’Europe, Graitson, Eric ; Hussin, José; Vacher, Jean-Pierre in Bulletin de la Société Herpétologique de France 141, 2012.