Humid Microclimates - some actual field data

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Humid Microclimates - some actual field data

Postby Tortoise Trust » Tue Apr 06, 2010 3:47 pm

There has been endless dispute on this subject, with some authors arguing that “faster growing hatchlings live under the cover of grass... providing a higher level of ambient humidity" and concluding that "areas with a humidity of nearly 100% for hiding should be provided to the tortoises at all times”.

Firstly, it is quite true that directly in the vegetation there is a somewhat raised ambient humidity compared to the humidity measured at, say 75 cm above ground in free air. Typically, free air humidity is <30% in most of these habitats and the humidity measured in vegetation at ground level is between 32-37%. It is not, however, anywhere near 100%. These photographs were taken yesterday, 05 April after the wettest winter in this region for more than 50 years. Rainfall was many times the average. The vegetation growth is also the best for many, many years. It is therefore the case that if extremely humid conditions were to be found in the micro-habitats used by juvenile Testudo graeca, you would certainly find them this year of all years.

This is the habitat. The yellow meter indicates the exact site of a juvenile Testudo graeca graeca overnight scrape/retreat under a clump of Esparto grass:

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Here's a close-up view of the tortoise in its scrape. It is 80% buried. The head and limbs are covered with earth, but the carapace is mostly exposed. This type of position is very typical. During hibernation or estivation they simply dig down deeper.

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We took precision measurements of the air humidity measured:

1) At the carapace
2) In the surrounding soil
3) In the ambient free air

As you can see here, this tortoise is in a faster growth phase.

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We have now measured many such tortoises in exactly these habitats, and can report that the average figures to date reveal:

Ambient Relative Humidity above ground: <30%
Relative Humidity in grassy microclimate: Circa 33-35%%
Subsurface Relative Humidity in substrate surrounding the juvenile: 55%

We are continuing to gather and collate this data, but so far the results are absolutely conclusive in that the claimed "100% humid microclimate" conditions supposedly essential to the avoidance of shell deformities quite simply do not exist in the natural habitat. The true figures are not even close. There is nothing remotely like a "damp sphagnum" microclimate anywhere in these habitats. This should be fairly obvious from the above photographs. Here's a few more examples of this habitat, Typical of Testudo graeca graeca in Almeria, Spain:

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The above shows a typical grazing area used by tortoises in Spring. This year the vegetation is exceptionally abundant. Tortoises will visit these areas to graze, but do not necessarily spend all of their time there.

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Snail shells are everywhere, and discarded shells are regularly eaten as a source of additional calcium.
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Re: Humid Microclimates - some actual field data

Postby Sue_Hardy » Tue Apr 06, 2010 4:42 pm

Interesting findings! Am I right in thinking that any air-breathing animal would find it nigh on impossible to breathe in 100% humidity anyway? I've been in 60% and that was pretty uncomfortable. Of course we feel it because we loose heat by sweating, which becomes more difficult with higher humidity but we also loose water when breathing.

This is making me feel better about the conditions I provide for the torts in my care, however I may have some way to go - I imagine the humidity would be greatly increased during the wet season in a monsoon area?

How did you spot that little tort in that environment? That must be down to experience! Brilliant!
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Re: Humid Microclimates - some actual field data

Postby Tortoise Trust » Tue Apr 06, 2010 5:22 pm

Graham got that one! :lol:

We don't have monsoons, here of course. It is a temperate zone arid habitat. It does go up during episodes of rain, but that is pretty infrequent!

Andy
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Re: Humid Microclimates - some actual field data

Postby Sue_Hardy » Tue Apr 06, 2010 5:54 pm

We don't have monsoons, here of course


:lol: well, not yet anyway...!

I was thinking of more of where G. elegans originate. A lot of the care advice written for that species suggests providing a high humidity environment most of the time. My feeling is that they will get increased humidity for 3 months or so every year and immediately following rain but it must evapourate off quite quickly. The rest of the year I would guess is quite dry.
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Re: Humid Microclimates - some actual field data

Postby Tortoise Trust » Tue Apr 13, 2010 7:55 am

Rainfall figures this year:

December 85.5
January 100.5
February 55.5
March 75.5

Total in 4 months : 317 mm which is about 12½ inches. Average annual rainfall is 285mm.

Average for this 4 month period is 138mm so it was 226% of the average.

Spectacular wildflowers this year as a result.
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Re: Humid Microclimates - some actual field data

Postby Dave K » Tue Jun 29, 2010 4:01 pm

May I ask if the relative humidity averages above are averages for a 24 hour period? Here in the UK I'm recording 30-40% increases between full sun and evening shade at ground level with light plant and grass cover. I haven't the accurate tools to take a sub surface readings but I'd be interested if sub strata, relative humidity remains at a stable percentage or increases at night.

Thanks
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Re: Humid Microclimates - some actual field data

Postby Tortoise Trust » Tue Jun 29, 2010 9:54 pm

Those are actual, typical readings measured around tortoises in daytime.

I do have both overnight substrate and free air measurements taken with data-loggers. I

Speaking generally (and this varies according to the time of year), in late spring to summer you will see an increase in humidity overnight, usually from about 9.00 pm until around 3.30 am, when it begins to decrease again. At the same time, temperatures reduce, then begin to rise again. This is basically the result of water vapour condensing out with falling temperatures, sometimes resulting in a light mist/dew. As I said, though - very weather dependent with strong seasonal shifts.

Right now, I am recording carapace temperatures on tortoises up to 40C between 12.00 pm and 6.00 pm, falling to around 17C at 3.00 am.

I have some new data recording at the moment, with humidity. I'll post the results.
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Re: Humid Microclimates - some actual field data

Postby Tortoise Trust » Tue Jun 29, 2010 10:21 pm

PS: Dave, you have a heck of a lot more moisture in the air in the UK than we do out here!

Even at 30C in the shade here, it is quite comfortable because the moisture in the air is so low.... the same temperature in the UK can be quite "sticky" and "close" feeling,, and in Florida, it feels like a steam bath.
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Re: Humid Microclimates - some actual field data

Postby Dave K » Tue Jun 29, 2010 10:46 pm

Oh absolutely agree. Just this morning it all decided to fall out of the sky at once. Tortoises enjoyed it though. Thanks for the info, it's great seeing this kind of data from the field.
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Re: Humid Microclimates - some actual field data

Postby Daryn » Sat Jul 07, 2012 4:42 pm

What a great read, thanks for the info all very interesting. Makes you wonder where these other people get there info from 100% humidity
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