Allerthorpe Common

Identifying Individual Adders (page 2)



	Head scale pattern on F56

METHODS

Within the author's records, each Adder previously found in the field is represented by one or more photographs together with a record card. The record card information consists of two types of coded information, diagrams of head markings (pigmentation and scales) and field notes.

Photographs are used as an obvious first reference and are used in the field. On finding a new individual the head marking and scale pattern are drawn onto blank templates using photographs of that specimen. A standard 8 times magnifying lupe is useful for this exercise. The head marking is drawn out only where the level of contrast against the background is sufficient to allow recognition, at some small distance from the snake e.g. 1 to 2 m . In Figure 1 a typical head marking is shown and for each Adder the apex of the dorsal zig-zag, inverted 'V', eye-lines and continuous area over the parietal, superocular, frontal, prefrontal and internasal scales are subject to individual variation. Figure 2 shows examples of head marking taken from record cards. In addition, coloured arrows are used to highlight unique features. For example, F5/SM/140598 has a ring of lighter pigmentation surrounding a darker centre on the frontal scale and a small patch of orange pigmentation arranged centrally invading both parietals. Figure 3 shows examples of head scale patterns, again taken from record cards, for the same individuals shown in Figure 2.

Field notes are added to each record when Adders are seen again. Information on when and where they were observed, general condition, evidence of sloughing etc. are transferred from a note pad to the cards after each visit.

The first piece of information consists of the letter M, F or U and a number and is intended for filing purposes only. The letter indicates whether the Adder is a male, female or unknown and the number is simply a file number. U or unknown sex is required when the shape of the Adder's tail has not been observed because it has covered its tail with its body, it has moved off too quickly or the Adder is immature. Next comes the place code, which is where and when first seen. Examples from record cards include F5/SM/140598 - that is a female, number 5, first seen on the small mound in the reserve on 14th May 1998 and F16/PT/080898 - a female, number 16, first seen adjacent to the picnic table along a forest ride on 8th August 1998.



Plate 1 - F56/GB/160803

A second piece of coded information allows rapid analysis and is an aid to finally confirming identification or a new listing. It is also listed in a file using a computer word processing facility which allows a match to be quickly obtained to confirm whether the snake is already known. Once again this data is a mixture of abbreviations and numbers that code for several visual features that can be observed on every snake, whether in the field or from photographs later. The first 7 number code refers to the number of head scales, which have proved to be very variable for the study group. Although there are several snakes, within the study group, that have the same number of scales within each scale group they are still different in size, shape and arrangement on the head.

In Figure 4 (a typical example) the 7 scale groups are shown. In the unusual circumstance where scales number more than 9, the number is underlined. In the case of the typical example, the 7 number code would be 6231332. From Figure 3 the head scale codes would be for F5/SM/140598-4231442 and for F15/OA/080898-62312332. Once again, it is certainly far easier and more accurate to collate this data from a photograph.



	Plate 2 - M23/OASM/010499

The following two letters refer to the main body colour of the Adders e.g. DB - dark brown, LG - light grey etc. and the next variable number of letters refer to the type of dorsal body marking (see Figure 5). Although the scale number should remain constant throughout life, the body colour can change depending on rate of maturity and sloughing. The names for the dorsal body markings are idiosyncratic and suggested by their shape and form. It may be that a particular Adder has an apex zig-zag that then turns into a mirror wave, which breaks up into ovals and then becomes diamonds in the tail, then the code would be ZZMWOD. The order is not relevant as the zig-zag can often break up into 'Ms' and 'Ws' in several places, being indispersed with oval markings a number of times. A large majority of the Adders have a distinct body stripe, where the characteristic zig-zag or parallel wave pattern has been lost. The body stripe may be solid - SS or have a lighter middle band - LS. Dorsal body marking may also be subject to change, as suggested above and for the same reasons. In which case, both pieces of information will be updated as the study continues.

To summarise the above, the Adder in Plate 1 is filed as F56/GB/160803 and F56/6331312/GB/ZZ and Plate 2 is filed as M23/OASM/010499 and M23/6251322/LG/ZZ

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