RAUK - Archived Forum - Refugia Survey

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Refugia Survey:

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Vicar
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Posted: 14 Oct 2004

Does anybody have any guidance on the appropriate spacing of refugia on uniform heathland ?

Aim of the survey is to determine the presence of species, not population densities.

Each site would be approx 25 hectares with a perimeter of around 2000m.

Apart from the usual issues of placement, permissions and situation away from the public gaze, I can't find any work on 'optimal' spacing of tins on uniform terrain.

16 tins over this area would give me about 100m separation - roughly.

All comments gladly received.

Vicar38274.050775463
Steve Langham - Chairman    
Surrey Amphibian & Reptile Group (SARG).
calumma
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Posted: 14 Oct 2004
If all you are trying to achieve is assess likely presence, I don't think that spacing really matters. Current Froglife guidelines recommend no more than 10 tins per ha. What really matters is placing each cover object in such a position that you maximise the chances of recording all of the species that are likely to occupy the site.

Lee
Lee Brady
Kent Herpetofauna Recorder | Independent Ecological Consultant

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GemmaJF
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Posted: 14 Oct 2004

Steve,

16 tins would be a little low in my guestimation for a 60 acre site even for presence absence. I would suggest 30 would be nearer the mark. Multiples of five also make analysis easier later on. In particular if you have a fairly featureless area it is more difficult to optimise a presence/absence study, compared to a site with obvious margins, banks, etc so you may want to compensate by going for even more tins.

Lee,

Doesn't the Froglife guidline of no more than 10 tins per hectare relate to relative population estimates, not presence/likely absence studies?

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Gemma Fairchild, Independent Ecological Consultant
calumma
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Posted: 14 Oct 2004
Gemma, it does - but it's still an attempt at standardising effort. The point I was trying to make was that if the site is 25 ha and you are following Froglife's guidelines there really should be 25 x 10 = 250 tins. So I agree that 16 tins is somewhat low. If a small number of refugia are to be used then spacing between tins simply isn't relevant. Far more important to place each cover object in an optimum position.
Lee Brady
Kent Herpetofauna Recorder | Independent Ecological Consultant

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GemmaJF
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Posted: 14 Oct 2004

Yep see your point Lee.

Steve, I think what Lee and I are both getting at is that one wouldn't evenly distribute the tins across the site with uniform spacing but would be more likely to bunch them in likely positions.

With a density of 10 per hectare you could reasonable cover the entire site with tins at even spacing. With a much lower density you have to optimise to where animals are 'likely' to use the refugia.

Lee pretty much taught me how to place refugia and I would recommend it is worth getting out to a site with an experienced recorded and seeing how refugia survey is set-up before going it alone. It takes a little experience to realise that what appears to be fairly uniform habitat to our eyes is featured to a reptile sometimes!

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Gemma Fairchild, Independent Ecological Consultant
Vicar
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Posted: 14 Oct 2004
Fair enough, I'll base the proposal for numbers on an estimate of the time taken to combine checking the refugia with a belt-transect visual encounter survey (walking between tins :P) for a 2-hour site visit.
Steve Langham - Chairman    
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Vicar
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Posted: 14 Oct 2004

OOps, I must have been typing as Gemma was :P

Basically I'm writing up a proposal/plan over the winter, with an aim of having a final draft by Xmas, which gives me the new year to co-ordinate with the various bodies/orgs.

Having started to write it up, its already looking quite the daunting prospect !, but there is a logic to the scale, driven by the goals. Having said that, even if nothing comes of the plan, I'm already finding it of vital experience.

Part of the process would involve what I call IPB, but basically inteligence preparation, site survey, identifying likely micro-habitat, extant records etc.

What would be REALLY helpful, would be a look over of what I am proposing (plan review) by persons far more experienced than myself (not too hard to find :P). Doubt I'll have a first draft ready until the end of the month tho.


Steve Langham - Chairman    
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frogworlduk
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Posted: 11 Mar 2011
what was the outcome of this? looking to place down some tins for presence/absence. was thinking some where along the lines of 30-40 on a 70 hectare site. sound about right?
Vicar
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Posted: 11 Mar 2011
OOh...

Lots of research on this since the original post!

Depends upon your habitat assessment. We've settled on a grid matrix of 1 tin per hectare for large area survey. Draft tin position is the middle of each hectare grid that has habitat suitable for reptile occupancy. Final position is the best assessed micro-habitat within 10m of that location (or a bit further if the micro-habitat is really bad).

The only trouble with bunching tins is that you tend to cluster tins on where you consider the best reptile habitat is. Unfortunately, even with lots of experience, the reptiles' view of what is the best habitat varies from ours! - The reason why people get so confident about 'good' reptile habitat is that few look hard in areas they consider poor habitat, so they re-inforce their intuition.

Having adopted the grid approach, we regularly find animals in habitat that amazes me. Smooth snakes regularly turning up in 2-inch heather!

Also, the grid system gives you  a much more efficient means of determining site-wide distribution.

So, for a 70 Ha site with all good reptile habitat, I'd say 70 tins. If half of the habitat is clearly unsuitable (whatever that means!), then half the number of tins.

If you end up with 70 tins, I'd suggest divide the site into 2 sub-sites. At those densities, with good visual survey effort between tins, I'd allow 1hr survey per 10 tins. 7 hours is a bit of a stint, even for me, so divide into zones and survey separately would be my advice.

Steve
Vicar40613.9484375
Steve Langham - Chairman    
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frogworlduk
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Posted: 12 Mar 2011
cheers steve. well it looks like i've got some fun ahead of me. sadly it's a berkshire site though! lol
Vicar
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Posted: 12 Mar 2011
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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GemmaJF
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Posted: 12 Mar 2011
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.
Gemma Fairchild, Independent Ecological Consultant
Vicar
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Posted: 17 Mar 2011
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 !



Steve Langham - Chairman    
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Suzi
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Posted: 17 Mar 2011
Content deleted by poster
Suzi40620.4561226852
Suz
GemmaJF
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Posted: 17 Mar 2011

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.


Gemma Fairchild, Independent Ecological Consultant
sussexecology
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Posted: 19 Mar 2011
[QUOTE=Vicar] OOh...

Lots of research on this since the original post!

Depends upon your habitat assessment. We've settled on a grid matrix of 1 tin per hectare for large area survey. Draft tin position is the middle of each hectare grid that has habitat suitable for reptile occupancy. Final position is the best assessed micro-habitat within 10m of that location (or a bit further if the micro-habitat is really bad).

The only trouble with bunching tins is that you tend to cluster tins on where you consider the best reptile habitat is. Unfortunately, even with lots of experience, the reptiles' view of what is the best habitat varies from ours! - The reason why people get so confident about 'good' reptile habitat is that few look hard in areas they consider poor habitat, so they re-inforce their intuition.

Having adopted the grid approach, we regularly find animals in habitat that amazes me. Smooth snakes regularly turning up in 2-inch heather!

Also, the grid system gives you  a much more efficient means of determining site-wide distribution.

So, for a 70 Ha site with all good reptile habitat, I'd say 70 tins. If half of the habitat is clearly unsuitable (whatever that means!), then half the number of tins.

If you end up with 70 tins, I'd suggest divide the site into 2 sub-sites. At those densities, with good visual survey effort between tins, I'd allow 1hr survey per 10 tins. 7 hours is a bit of a stint, even for me, so divide into zones and survey separately would be my advice.

Steve
[/QUOTE]

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.

GemmaJF
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Posted: 19 Mar 2011

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.

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Gemma Fairchild, Independent Ecological Consultant
Vicar
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Posted: 20 Mar 2011
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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GemmaJF
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Posted: 20 Mar 2011
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.GemmaJF40622.4069328704
Gemma Fairchild, Independent Ecological Consultant

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