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Refugia Survey |
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Vicar
Senior Member Joined: 02 Sep 2004 Location: United Kingdom Status: Offline Points: 1184 |
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I should have mentioned that what we do is not pure absence/presence, although that is a key aspect.
It's about advice to the land manager, so site-wide distribution also matters. By gridding rather than clustering, we help reduce the bias of tin placement (a bit) in the final statistics, which helps when calculating the probable absence. And of course we cover more area in a consistent manner. |
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administrator
Admin Group Joined: 01 Jan 2007 Status: Offline Points: 10 |
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I like the take on 'good habitat'.
"We find smooth snake in two inch heather".. um that's only 'cos you put a tin there and now it's really quite good habitat (cover/warmth) when it used to be just OK for a quick forage now and then Just teasing, interesting read. I must admit I'm a cluster person myself, but would certainly consider this approach on large sites in future. |
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Vicar
Senior Member Joined: 02 Sep 2004 Location: United Kingdom Status: Offline Points: 1184 |
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20-30 refugia is exactly our guidance, through trial and error (for volunteer surveyors), but not from the logistical point of view, as our ARG handles the logistics, and most of our sites are set up for long-term monitoring.
20-30 tins (2-3 hours of survey at the densities discussed) seems to be the sweet-spot for volunteer surveyors. Enough to get stuck into and to provide value, but not so long as it takes up their whole day. Interesting convergence ! |
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Suzi
Senior Member Joined: 06 Apr 2005 Location: United Kingdom Status: Offline Points: 1025 |
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Content deleted by poster
Edited by Suzi |
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Suz
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administrator
Admin Group Joined: 01 Jan 2007 Status: Offline Points: 10 |
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Unfortunatley Steve 'Saliha's' post is nothing more than a very thin veil for the advertising in their signature.
The passage is a copy and paste from the NARRS site: http://www.narrs.org.uk/widespreadreptile.htm Now Saliha, do the right thing and waste somebody elses band width. |
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sussexecology
Senior Member Joined: 30 Sep 2010 Location: United Kingdom Status: Offline Points: 411 |
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Also the other point is that if you place the refugia in a grid and regularly spaced, rather than placing them just anywhere, they are much easier to find when you come to do the surveys. i tend to put refugia out in good habitats as well as poor habitats, and as many refugia as possible. |
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administrator
Admin Group Joined: 01 Jan 2007 Status: Offline Points: 10 |
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Steve do you have the data for how many animals per hectare are recorded on average for each of the widespread species using this survey protocol? It would be interesting to compare to a cluster survey based on the old 'I know it's good habitat because I've been doing this for years and have no trouble finding animals' approach. Having said that we survey at much higher density than 1 refuge per hectare usually, and few sites I've worked on were uniform enough for a simple grid. (too many woodland areas, roads in the way etc). To date what info I had on using grids indicates for reptiles the results were poor. One of the advantages I've found of say putting out a loose group of five refugia is that on any given day/time of day one may have the advantage over another. Where as one might be prone to shading for part of the day etc. (a simple example is a loose group of five refugia in our back garden, any one of the five will produce Zv, 2 produce Af, but only one ever produces juvenile grass snakes, the hottest one, on a low south facing bank). Note this is an area about 30ft x 20ft but still the placement is critical for one widespread species. It's also the one least often used by the Zv! I did figure once I could comfortably check 200 refugia in an hour, including stopping to record details, just trying to work this in the context of a consultancy style presence/absence exercise where to be honest the time put into visual suvey (other than for adder) tends to be far less productive (though none the less interesting) than checking refugia. Just to add, regarding the reinforcement of 'good habitat', I have data of site clearances (where regardless of initial survey the whole area was covered in a uniform grid five paces apart each way) clearly showing the highest density of animals came from the original survey positions. This gives me a dilema, either I actually am good at spotting good reptile habitat, or does placing refugia for initial surveys actually attract animals to, or compel them to stay in those areas I'm certainly now in the habit of concentrating presence/absence surveys around mitigation areas whenever possible (i.e. to survey in adjacent similar habitats) and also very reluctant to keep refugia down longer than needed to get my base data in an area that will eventually be subject to capture works. Edited by GemmaJF |
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Vicar
Senior Member Joined: 02 Sep 2004 Location: United Kingdom Status: Offline Points: 1184 |
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I certainly have the data to be able to extract mean animals per hectare, but it wouldn't be comparing like with like.
As I mentioned earlier, we are faced with much larger areas than what I expect is usual from a consultancy perspective (very large projects exempted). Also, our surveys are triple hatted: Presence/absence, Site-wide distribution and long term monitoring. Eg Frensham is about 400 Ha, similar for Hankley and Thursley, and Ash is the size of all three together! It's hard to predict where a habitat management plan will need to be tweaked in the future, such as a grazing regime or deforestation, so good coverage across the entire site is what we'd like to aim for. As we know, reptiles usually occupy foci, rather than exhibit homogeneous distribution, so having a combination of refugia and visual per hectare is a compromise, but it's about the maximum density we can resource. 5 tins in each hectare would be great...but then we'd need to lay and survey 5 times the number of tins! - let alone replace them as they rot, or cover just one fifth of the area. As said, it also has the benefit of challenging received knowledge with animals turning up in what I would consider unlikely places. The Ca I mentioned on Ash are so far from what one might consider suitable habitat, that you'd need binoculars to see the closest bush! It also minimises statistical bias when comparing sites. I am absolutely not suggesting this is appropriate for consultancy work. |
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administrator
Admin Group Joined: 01 Jan 2007 Status: Offline Points: 10 |
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Ah that's my point Steve, I know we're not talking the
same thing, I was just interested in the comparison. Particularly in terms of survey effort and numbers of animals recorded. For sure only putting tins in areas people perceive as good habitat is going to mean other areas get ignored though I guess from my view my definitions continue to broaden! Though sticking with a grid is a simple solution to remove any surveyor bias. My interest is more finding a workable protocol for volunteer surveys in Essex. I think few volunteers could work to the level that's 'normal' to me and I only have so many spare refugia I guess I'm also looking at what is more useful - intense detailed survey of particular sites, or a better understanding of where in the wider countryside reptiles exist in Essex. I think both have there uses, the first though is already covered in the county, the second, not at all as far as I know. Edited by GemmaJF |
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Suzy
Senior Member Joined: 06 Apr 2005 Location: United Kingdom Status: Offline Points: 1447 |
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I've searched the forum and can't find the bit I want where the pros and
cons of different materials are discussed for use as covers. Please can
someone enlighten me? Also the best sizes to use. I've noticed that
smallish pieces rarely have anything under them, although they are meant
for snake monitoring.
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Suz
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