Refugia Survey

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.

Edited by Vicar

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?

Edited by administrator

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!

Edited by administrator

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.

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


Edited by Vicar