ABSTRACT

During the past three years the author has regularly visited a small nature reserve in East Yorkshire to see the colony of Adders Vipera Berus living there. In order to monitor the behaviour and movement of individual Adders during the year, a procedure has been developed which facilitates identification without handling or significantly disturbing the snakes. So that each Adder is correctly recognised, with some degree of certainty, whether from a fleeting glimpse or from photographs, several working aids to identification have been used so far. Work is in progress and record keeping has involved the use of codes using abbreviations and numbers. Other workers have used the distinct head markings of adders to identify individual snakes; this study uses the same technique, together with the arrangement, shape and number of head scales, body colour and dorsal markings.

INTRODUCTION

It is well known that Adders are highly variable in their markings and no two Adders are identical (Smith, 1951; Frazer, 1983; Arnold & Burton, 1978; Sheldon & Bradley, 1989; Evans, 1992). Head markings can be diverse and have been used previously by workers identifying Adders in the field (Sheldon & Bradley, 1992). Head scale number and arrangement can also be highly variable and extremely useful as identification guides (Sheldon, pers. corres. 1998). Body colour and dorsal markings can also be variable.

Although head markings can be the most obvious and 'easy to view' feature between two individuals, they do not always appear grossly different in the field. Body colour and dorsal markings can be useful identification aids 'in the field', but only for a few unique individuals. The shape, arrangement and number of head scales can be significantly different from Adder to Adder, but require the observer to be close to the Adder. It is usually more convenient to examine these features on photographs after a visit. Using scale counts, dorsal marking type and colour code a simple reference system has been developed to improve recording and as a check against previously recorded individuals.

STUDY AREA

The main area consists of 5.7 hectares of open heathland, surrounded by coniferous forestry on three sides and turf-growing land on the fourth. The reserve is managed by Yorkshire Wildlife Trust. It consists of mixed areas of vegetation with several areas of Heather, Calluna vulgaris and Cross-Leaved Heath, Erica tetralix, separated by Tufted Hair-Grass, Deschampsia caespitosa. There are also areas of Bracken, Pteridium aquilinum, which are kept under control. Silver Birch, Betula pendula, and Gorse, Ulex europaeus, grow in small stands with Scots Pine, Pinus sylvestris, being represented by single maturing specimens. The birch has been greatly reduced within the reserve and the cut branches and twigs have been stacked as habitat piles of various heights. Adders are frequently found together in two small areas, a small raised mound surrounded by heather and an open area containing a low habitat pile of birch branches surrounded by Tufted Hair-Grass. Individual Adders are found throughout the reserve, either basking in open areas or in the front of vegetation e.g. adjacent to dense groups of birch saplings or gorse. Juvenile Adders are frequently found away from the communal areas sitting on grass tussocks, tree stumps or supported in old heather. Away from the reserve Adders can be found along the transecting forest rides. A particularly good area is along the line of high-voltage electrical cables, supported by pylons, which runs parallel to the pine forest. In order to maintain access to the pylons the area is kept clear of potentially tall vegetation and Adders are found basking in open areas or on grass tussocks.

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