In all seven landscape spaces in Northrhine-Westphalia, the grass snake (Natrix natrix) is classified as in danger of
extinction [Feldmann & Geiger 1986].
The sensitization by the movements for the protection of the environment resulted in a larger tolerance towards the grass snake; nevertheless, this hardly has a positive effect on its population due to the continuing destruction of its habitat. Since the turn of the century, 'dozens of mating grass snakes' and 'tangles of snakes' have rarely been observed, as former authors described.
1. The destruction and change of (grass snake) habitats
Today, many plant and animal populations in areas of industrial concentration, among them the grass snake, are forced to survive in ever smaller, more or less natural areas.
In order to realise to which extent landscapes are build up, it is worth the effort to read the statistical yearbooks of districts and municipalities. The Statistical Annual Reports of the city of Wuppertal (1975 abd 1989/90) reveal that between 1975 and 1990 the area of a soccer field (62 ha annually) has been build up every third day on average. Therefore, the remaining habitats in congested areas are more and more important.
2. The importance of streets for grass snake populations
Streets cutting through the habitat of grass snake are of twofold danger to the population:
a. When located in river valleys, even streets with heavy traffic are crossed by the grass snake during seasonal migrations [Völkl 1991]. In Wuppertal, mainly young animals and male snakes are run over [Eckstein unpublished.].
b. As a second group the animals which are affected are those which rest on less frequented streets for thermoregulation. The dark surface of the street absorbs heat rapidly and maintains it. These streets become dangerous for the grass snake mainly during morning and evening traffic [Völkl 1991, Eckstein unpublished.].
A growing knowledge about habitats and habits of the grass snake enable a limited compensation of negative effects.
Since the destruction of natural habitats (a major problem in congested areas due to the continuing concentration of cities) advances constantly and a change of the situation in the near future cannot be expected, the only remaining possibility from a realistic point of view is to change (shape) the "remaining" habitat in such a way that a high diversity of authochtonus plant and animal populations is created.
The radius of action of the grass snake consists of a variety of biotic and abiotic factors which have a different importance for the population. The knowledge of these elements make it possible (within limits) to draw conclusions as to the "improvement" of existing habitats.
Water bodies play an important role for the success of procreation of amphibious animal populations. Since amphibious animals are the main nutrition of local grass snakes [e.g. Eckstein 1993, Hemmer 1955, Mertens 1992], their spawning waters and land habitats form an important part of grass snake habitats.
The banks of water bodies should show natural vegetation as well as submerse vegetation [Mertens 1992]. The author also underlines that the grass snake uses the water body for thermoregulation. During summer, some animals could be found in the water during cooler temperatures in the evening or at night, since the water was warmer than the ground.
Juvenile grass snakes need areas of shallow
water and pools with a depth of approx. 5 – 20 cm for hunting salamander
larvae and tadpoles.
It is important that the banks should be shaped in a large variety offering sunny spots as well as places to hide. Anthropic disturbances should only be minimal (no hiking trails on the banks, reducing disturbances (destructions) by fishermen to small areas).
Summer habitat: The summer habitat of the grass snake are humid meadows, extensively used grassland, hillsides exposed to the sun and open deciduous forests which are normally close to ponds, pools, ditches, slowly flowing brooks or rivers with areas of stack water.
As resting and sunning places the grass snake often uses spots with little vegetation, dead wood, stones and dead vegetation as well as dung, compost and mowing heaps in which fermentation heat has created a humid and warm climate. The grass snake avoids areas without vegetation [Eckstein 1993, Mertens 1992].
Bush lines have an important function as migration routes and hiding spots; the role of thorny blackberries (Rubus fructicosus agg.) and raspberries (Rubus ideaus) is especially important [Mertens 1992].
The home ranges of several animals can overlap to a smaller or larger degree [Eckstein 1993, Madsen 1984, Mertens 1992], and it was also not possible to observe any intraspecific aggressions or comment fights [Eckstein 1993, Kabisch 1978]. The factors for a limitation of population size must still be studied further.
Does the Grass snake hide from civilisation
Obviously, it is not any problem for the grass snake to adopt to partially or completely anthropic formed habitats [Mertens 1992, Eckstein 1990 u. 1993]. For example, a population in Marburg lived in an artificially laid out part of the Botanical Garden [Mertens 1992]. As already described above, the grass snake often uses possibilities created by men for hibernation and egg deposition. Therefore, it is in my opinion not appropriate to speak of a hiding of the grass snake from civilisation, although the snake often reacts negatively towards frequent disturbances of its habitat [Ritter in writing. mid 1990, Eckstein 1990 and 1993].
Changes of the grass snake habitat
After the last glacial period the grass snake probably lived mainly in large and extended river valleys and in swamps, but only a few swamps existed in the Bergisches Land.
From the 6t to the 13th century, the grass snake might have experienced a strong expansion of the areas in which the snake can live due to extensive clearing.
Literature between 1830 and 1900 shows that the grass snake used anthropic created possibilities such as dung heaps, stables and farms etc. for the deposition of eggs and hibernation in spite of a still existing wilderness.
Today, we can observe a decrease of the grass snake populations in extended areas.
In my opinion, due to agriculture and pasture farming until the beginning/middle of the present century and the corresponding creation of a variety of structures and habitat types, the grass snake has been able to use a larger area, not only in the Bergisches Land, than before colonisation by men. Nevertheless, because of the building up of large areas, the change of working methods in agriculture, the consolidation of arable land, and the canalisation and poisoning of rivers and the environment, the grass snake has suffered great damage.
During the beginning, the grass snake probably lived in and next to river valleys. Due to the extinction of nomadism, the end of migrations approximately in the 6th century and the clearing of forests for crop and stock farming the habitat increased enormously.
In the 19th century, the grass snake is found still frequently in spite of regional persecution and during this period it already uses farms, cellars, stables and dung heaps for egg deposition and hibernation.
Since approximately the middle of the present century, strong negative changes took place due to constructions on large areas, changes of working methods in agriculture, consolidation of arable land, regulation and poisoning of rivers.
The only remaining possibility, at least for congested areas, is to shape and equip the habitats of the grass snake. This must be done according to its necessities, as far as they are known, in order to compensate negative influences.Extracts from: Eckstein, H.-P. . Lebensraumveränderungen und Schutz der Ringelnatter im Bergischen Land - In: Gruschwitz, Kornacker, Podloucky,Völkl & Waitzmann (Hrsg): Mertensiella, Bd. 3, Verbreitung, Ökologie und Schutz der Schlangen Deutschlands und angrenzender Gebiete, S.199-210, Bonn.