RAUK - Archived Forum - Individual ID technique advice

I have recently become involved with a grass snake project, hence I am seeking advice regarding the least intrusive method of recognising individual animals.  My aim is to do so by sight only on occasion and avoid uneccesary capture and stress to the animals wherever possible.  I have so far already benefited from Gemma`s experience who has given me some very interesting tips.  Thank you for that Gemma, it was both helpful and very much appreciated. 

I was asked to identify a safe and viable population of grass snakes in order for a doctor from the conservation ecology research team of a nearby university to begin a study of the animal`s diving behaviour.

I have since identified a total of six sites that are local to me that hold colonies of grass snakes of varying density.  Access permission has been granted to carry out the work on two of the sites so far with a third likely to be granted very shortly.  We are at the stage of laying down discretely placed refugia at two of the sites to begin the "getting to know individuals" stage of the project.

Due to the nature of the study, it is mandatory that individuals are recognized and recaptured on occasion.  To briefly explain, a small device is glued to the nape of a large female, (males are generally considered not large enough) which records the regularity at which the device has been submerged, the period of time that each dive endured, as well as the time of day, depth and temperature.  I have seen the results of a similar device when used in a study of mink diving behaviour and the information gained was both detailed and useful.

The device is lost with each slough cycle so as close an eye as possible must be kept on those individuals which have been "tagged" so to speak.  Obviously a milky female will not be chosen to have a device fitted, but a recently sloughed animal will be.  Then the animal must be monitored and a judgement made regarding when the device is best retrieved.  It is predicted that a percentage of the devices will be lost of course!

So all I am after really is an opinion from anyone with experience of N.natrix as to the best way to differentiate between individuals.  I was thinking of head and dorsal images perhaps?  Considering that the animals must be captured and recaptured to retrieve the information, I would like to minimize the amount of captures in between the fitting or removal of the device.  If I am able to recognize an animal by sight only in order to assess the stage of the sloughing cycle, then this would surely be better for the animal concerned as well as easing my conscience!

Peter

Peter,

I hope by now that you have my PM?

Further thought: How will you begin to record when sloughing begins? It may mean you will have to take a few females into temporary captivity until they shed, in order for you to kick the project off. I've listed the other difficulties. How enclosed are the sites (Pm the info if detailed). Is there likely to be overlap of one home range and another? Or is one group pretty much isolated from open fields, rivers, canals etc?

Here are a few examples of what youre looking for in a mug shot...... And what you will try to avoid.

Although these were taken mid-slough (which you are going to avoid anyway!)

You'll need both profiles and try to get in some neck and collar details at right angles to the camera. There is a knack to that.

Overhead shots are good as the scales differ quite a lot toward the back of the head.

And try not to get them too close so that the neck and scales come out of focus.

See what it mean? Not a lot of good for the records! Drop me a PM line if you want a hand down there.

Cheers

rob

Rob,

Thanks for the response.  The images and advice will no doubt be extremely helpful.

The sites so far identified do vary greatly as regards isolation from canals etc. Some are more suitable than others.  We are at the earliest stage imaginable with this project, and I expect to be spending years at it, maybe before any devices even get attached!

Your offer of help is greatly appreciated.  I shall now reply to your PM.

Here are some of our first attempts, courtesy of Mark B.  Some will prove more useful than others but not at all bad for a first attempt and considering how lively the animals were.

Peter,

great that you've started recording. First pic from top looks like a male, third, a young female, is that what you figured? Don't forget that you'll need both profiles left and right.

Good hunting

Rob

Hi Rob,  did get both profiles of 6 animals but didn`t want to flood the forum with pictures!

We lost count of the natrix at this site, a conservative estimate would be 18.  They ranged from the very young to a 30" animal but nothing bigger.  The big adults don`t seem to be using the refugia at this site.

Another tip for taking ID shots is not to take them against a very pale background. This causes the camera to darken the contrast on the snakes head, and can obscure some of the scalation detail. Taking the shots against a dark background (grass, wood, etc.) will prevent this problem.

Ax.

You need to take a section further down the snake on the ventral pattern say 15 to 20 scales to get a good number of markers for identification.

You could also use paint markers aswell which people use to reduce the amount of capture within a study - a dot or a number painted on the back of the snake will help you pinpoint individuals in the field without the need to photograph the animal you can id them from individual numbers rather than mugshots which would cause disturbance getting close to the animals for a shot - Paint marking is being used at a site in Hampshire with adders during the spring and it is very effective for volunteers to spot animals and can actually tell where animals have come from.

An italian study used this method to study snakes which was presented at the BHS snake scientific meeting. He got a rough ride from some of the audience - you shouldnt be doing that blah blah! but he countered the argument with the survivability of snakes in the study plus the reduced need to capture snakes is a major benefit

I have been studying grass snakes at my local nature reserve and my local farm - I have had my first recapture this year! see examples of ventral shots below

Firstly in answer to Axel, ordinarily i'd agree with your comments about pale background to darken the subject etc, but sometimes in the field in deep shade its so dark that to darken the subject would mean detail is lost.

Moving on to Jon's comments. Jon, I cannot believe you are still doing the ventral scale thingy! The point is that you HAVE to capture them repeatedly with the ventral technique just to find out which one it is you're holding!!

And look again at the way the snakes in the pics are stretched! I simply cannot agree that there is any merit with doing that. As for painting snakes - well i'd much rather go by natural facial markers, its not that difficult to achieve, but paint, ok until the snakes slough, then what, paint them again?

Rob

Firstly in answer to Axel, ordinarily i'd agree with your comments about pale background to darken the subject etc, but sometimes in the field in deep shade its so dark that to darken the subject would mean detail is lost.

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Hi, maybe I wasn't clear, but I the point I was trying to make was that pale backgrounds can darken the subject and obscure detail. This was found to be a problem when I was involved in surveying Z. longissima at the WMZ. When photos were taken against a white background details of head scalation patterns could not be seen clearly. When we switched to photographing snakes against a dark brown background the problem was rectified. Incidentaly, all photography was done indoors so shade or bright sunlight was not a problem.

Ax 

Yep I am still using ventral markings it is by far the best method (in my opinion) for identifying individual snakes as the number of markings are more distinct that facial markings which are not as numerous and so misidentifications can occur.

So I am sticking with ventral markings especially during translocation or relocation projects which I am involved in as you have to capture individual snakes in this work so I can identify animals in later monitoring surveys.

There are series of methods which are available to the field worker, using the facial markings may work but you would need to get a good close up shot of the head when identifying animals in the field - how often would a snake stay still enough for this id shot to be taken or viewed through binoculars?

Laying down tins in the summer helps to reveal snakes and you can safely capture them. I do not stretch the snake I hjold the head steady while supporting the rest of the body on my thigh or the ground in some cases.

No harm is done and you dont have to capture the snakes all the time to id them - you soon get your eye in o the different shape of collar  size, age, sex etc

The paint marking is a very useful tool as you dont have to capture the snake to mark it - well this works in adders not sure about grass snakes. You can use an extended paint brush to mark the dorsal surface of an adder while it is laying out basking - you can get quite close to an adder in the spring emergence. I am planning on tracking movements by marking snakes at their hibernation area and then spotting them when they have moved to surface dens in the local forest near here.

Grass snakes around the farms near my house are very flighty and so capture is necessary to look at each individual, process it SVL, weight etc and to see what food items it has consumed.

Before you start again about why do you do that well we need to know what amphibians frequent the diet as the local toad population has crashed according tot he toad crossing data - I have found that snakes are still finding toads very easily around the farm which is a good sign.

Still it is up to the original poster what he wants to use for his study I was merely jsut putting together ideas.

J 

We have to stay open minded and ventral scale counts (first 20) was one possible technique for ID I put in a PM to the OP, Jon has provided a very good illlustration of what is required.

Lets not get into right and wrongs but discuss the methods available.

We are all pretty experienced folks on here and know how to handle the animals without harm, if a better less obtrusive method comes up I'm sure each of us would give it consideration if it is practical in the circumstances of our study (i.e. some handling during mitigations cannot be avoided so it is good practise to collect the data then, if it will be of future use). Scanning neos in my garden has been going very well, minimal handling and it clearly isn't scaring them off or harming them though I'm sure 'squishing' them sounded a bit drastic to some people, it really is the best way to do it and unless you know the technique and how little restraint is actually involved it is hard to really criticise it.

Glad you`re getting some data from the neonates in your garden Gemma.  It certainly is something else to be able to do so literally on your doorstep.  You must be chuffed to pieces, I know I would be.

It`s been of great interest and benefit to me to be able to draw on everyone`s experience in this thread, and I am grateful to all concerned for taking the trouble to respond.  We have so far been taking head and neck shots and both profiles, and we did also take ventral shots  (vent to tail basically) before reading the suggestion to do so purely from the point of view that my lack of experience of recognising individual animals means that at this stage, I feel that I need as much to compare as possible to be sure of not making a mistaken ID.

I must admit we have been not bothering to do so with animals below a certain size.  Rightly or wrongly, this is just personal choice at this stage in the proceedings.  We have a few reasons not to do so at present, which may well change as time and experience increases.  One lazy reason right now is that at one of the sites at least, an estimated 80% of the animals that we have so far found are very young and delicate, and to collect data for these small animals would also be extremely time consuming, considering that last week we found 18 in a 30 minute period.

Thanks again for everyone`s comments and I hope that this interesting discussion continues with the theme of available methods so far used.

Ok, so we agree to disagree on that Jon and let Peter come to his own conclusions as to the most practical method.

R