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Om luftfuktighet

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Några citat från Andy Highfield om luftfuktighet:

One of the moderators on a French site insists juveniles must have 70% humidity.

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Don't you just love it when people get all dogmatic and "insisting" on things?

It's more complicated than that. There is a big difference between the environments juveniles experience in sub-surface microclimates and those they experience when active and grazing, for example. A general air humidity level of 70% is very high and could easily cause other problems. That is closer to the air humidity levels suitable for a tropical species, such as a Redfoot or even a Green iguana. This might explain the microclimate issue:

http://www.tortoiset...croclimates.htm

I have measured the actual RH experienced by Testudo hermanni in both France and Spain myself, incidentally. When buried (or partially so), humidity next to the animal can range from 50-70%. From what I could tell, they only experienced that when innactive (except when dictated otherwise by weather conditions). Above ground, moving around, I measured RH from 25-40% which is pretty "dry".

It could be argued they need to self select between the two. Forcing them to be in one or the other would not be advisable.

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As far as I'm aware, the air humidity in the wild would only be around the 30% mark, however, under bushes and in the ground, the humidity would increase as these are shaded areas and any water would take much longer to dry out than it does in the open.

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The measurements I've made are very clear that when buried (or partly buried), yes - the humidity around the tortoise is higher. No doubt at all.

Moving on from that to "under bushes", I'd have to say there was zero measurable difference between what is found there and in fully exposed areas.

There may have been a one or two percentage points difference (possibly) but that was not accurately measurable and was within the room for error of the equipment used.

The plants in these areas are typically of a type designed NOT to give off moisture from their leaves in any great amount... if they did, they'd dry up.

So, they tend to be of thorny/oily herbaceous drought resistant variety.

Being under vegetation cover certainly provides shade, which is important, but in the typical habitats and climates in question, it does not appear to convey much benefit in terms of extra humidity.

Andy

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It is critically important to address one very common piece of misinformation in this context. It has been claimed that juvenile tortoises (for example, Testudo graeca) spend most of their time in the wild in “humid” microclimates where ambient conditions are in the range of 90-100% RH. This is completely false. One part of our study involved taking many thousands of measurements in the natural habitat to establish the actual conditions experienced. Our methodology involved the use of miniature automatic data loggers that recorded both temperature and humidity with a very high degree of precision. We took recordings over a complete 12-month cycle in several key habitats. We also attached loggers to tortoises and recovered them later to collect the data. In total, we collected 18,000 data points detailing humidity alone. What we found - in brief - was that juvenile tortoises were not experiencing substantially different levels of humidity than adults. While it is perfectly true that tortoises make extensive use of selected microclimates, the levels recorded in these were in the range of 34-60% RH. The sole occasions when levels in excess of 90% were recorded were during thunderstorms and episodes of rain. In the semi-arid environments of Ameria and Murcia (which are very similar to those found in most of North Africa) rainfall is not a regular occurrence, even during peak periods of tortoise activity. In total, we found that tortoises were only exposed to levels of humidity that could reasonably be described at “high” (80%>) for 2% of the total time recorded. While foraging humidity could be as low as 20%, but this was followed by retreat into vegetative microclimates where typical levels average around 45-50%.

(Andy Highfield)

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Regarding humidity. There are (mostly on some American tortoise forums) some absolutely crazy people who continue to insist that arid habitat species should be kept at near 100% humidity 24/7. This is completely insane and bears no relation at all to how these animals really live or what they need. A humidity increase for a brief period overnight, however, is much closer to what is experienced in nature and is potentially beneficial. It depends what your "starting point" is, however. If you are in an already semi-humid environment it is not necessary and could (in some circumstances) still cause a problem, because they also need some "dry time" (in simple terms). However, if your humidity during the day is below about 40%, then an overnight increase can help to "counter balance" this.

The levels we see are typically:

Outside, daytime, open air at 10cm above ground in full sun: <25% RH
Outside, daytime, under vegetation or in shallow scrape: <40% RH
Outside, daytime, buried in ground: <55% RH

Over night, there is usually an increase in RH that may cross the dew point as temperatures drop, with maximum levels seen from 3-6 am, so just a couple of hours. During this period there may be dew formation and RH in free air can be 80% or so. As soon as the sun rises, these levels return to the low figures given above. This does not occur every night, or at all times of year, but is quite common.

(Andy Highfield)

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