night time lows.

Anyfoot

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One aspect of tortoising I've neglected to look at is lower temperatures at night.
I just don't bother with a drop in temps with my redfoots or homeana. Maybe this is an area I need to look at.
For my radiated I've got temps dropping at night.
For the last few weeks I've been watching the weather in Madagascar(Toliara). Basically at this time of year it's around 86f/91f and 60/70% in the day and 75/80f and 80/90% at night.
I'm curios of what impact having night time lows has on our tortoises.
Also would the micro climates that the babies live in be more stable through day and night?
 
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CharlieM

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I’ve used a temp gun in the early morning and my tortoises that dig into the mulch substrate under a hide are 10-15 degrees warmer than the nighttime low. My tortoises can go into a hide under a covered and enclosed area. If I add a tarp over the entire enclosure the tortoises stay even warmer. The ground holds heat during the rare and brief cold snaps we have in Florida.
 

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One aspect of tortoising I've neglected to look at is lower temperatures at night.
I just don't bother with a drop in temps with my redfoots or homeana. Maybe this is an area I need to look at.
For my radiated I've got temps dropping at night.
For the last few weeks I've been watching the weather in Madagascar(Toliara). Basically at this time of year it's around 86f/91f and 60/70% in the day and 75/80f and 80/90% at night.
I'm curios of what impact having night time lows has on our tortoises.
Also would the micro climates that the babies live in be more stable through day and night?
Craig,

The best data I've seen on this can be extrapolated from extensive studies made for passive heating/cooling systems using the thermal mass underground to more efficiently stabilize systems. Also lots of good agricultural reports on ground temps worldwide that I've read.

It has been established that the ground temperature just 0.5m below surface is quite stable even with very wide daily air temperature swings. At just 1m deep the temperature averages =/- 2° of the daily average air temperature. There is a lag of just over a month as the seasons and average day temperature changes. At just 0.2m below surface, the ground temp stays within about 5° of the daily average. So with your figures above, with a high of 88° and low of 77° we would see an average daily temp of about 83°. A tortoise in a shallow pallet under a bush would probably experience pretty stable temps overnight in the range of 80°-83°.

I've looked at data for areas for radiata, pardalis, sulcata, and platynota in the past. All are amazingly similar in what the average ground temps would stay. There is a difference in the width of air temp high/low swings, but the average temperatures and therefore ground temperatures are interestingly in the same ranges.

If you think about it... We have found almost all tortoise species eggs are best incubated at a quite narrow temperature band. And that would indicate optimal temperature for best metabolic function!!
 

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Craig,

The best data I've seen on this can be extrapolated from extensive studies made for passive heating/cooling systems using the thermal mass underground to more efficiently stabilize systems. Also lots of good agricultural reports on ground temps worldwide that I've read.

It has been established that the ground temperature just 0.5m below surface is quite stable even with very wide daily air temperature swings. At just 1m deep the temperature averages =/- 2° of the daily average air temperature. There is a lag of just over a month as the seasons and average day temperature changes. At just 0.2m below surface, the ground temp stays within about 5° of the daily average. So with your figures above, with a high of 88° and low of 77° we would see an average daily temp of about 83°. A tortoise in a shallow pallet under a bush would probably experience pretty stable temps overnight in the range of 80°-83°.

I've looked at data for areas for radiata, pardalis, sulcata, and platynota in the past. All are amazingly similar in what the average ground temps would stay. There is a difference in the width of air temp high/low swings, but the average temperatures and therefore ground temperatures are interestingly in the same ranges.

If you think about it... We have found almost all tortoise species eggs are best incubated at a quite narrow temperature band. And that would indicate optimal temperature for best metabolic function!!

You remember how when you were a little kid and a beloved family member (Mom, Dad, Grandparent, Aunt, Uncle, etc…) would read you your favorite bedtime story. Remember how good that felt?

That is how I feel about the story above. I just love it every time I read it.

When the cynics ask: "Why do you keep them 80 degrees at night? Its not 80 degrees in the wild every night…" I just remind myself of my favorite tortoise bedtime story where Mark explains the concept of ground temps vs. weather station readings from 2 meters above the ground in open areas with no kind of cover.
 

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One aspect of tortoising I've neglected to look at is lower temperatures at night.
I just don't bother with a drop in temps with my redfoots or homeana. Maybe this is an area I need to look at.
For my radiated I've got temps dropping at night.
For the last few weeks I've been watching the weather in Madagascar(Toliara). Basically at this time of year it's around 86f/91f and 60/70% in the day and 75/80f and 80/90% at night.
I'm curios of what impact having night time lows has on our tortoises.
Also would the micro climates that the babies live in be more stable through day and night?

I don't know RFs, but from what I have read of other people's experiences, they thrive without a big drop in night temps.

For all my tropical species (Sulcatas, leopards, stars, pancakes…) I always have a night drop, but usually not below 80 for little ones. In summer, I let ambient creep into the mid 90s in my enclosures, and in winter ambient will creep into the mid 80s during the day. At night, year round, temps drop to about 79 at night. I don't have a lot of radiata hatchling experience, but I just baby sat some for a month, and this worked well for them too.

I recently got to tour the facility of a friend who breeds radiata, and he told me that he lets the adults drop down in to the mid 60s at night and has been doing it that way for years.

To me, discussions of drops in night temps are most relevant in discussions of species that would experience these significant drops in the wild. Basically any species from a temperate Mediterranean climate. Testudo, Gopherus, SA leopards and Chersina. When indoors, I let Testudo species hatchlings drop into the high 60s or low 70s. Daytime ambient for them will be around 80 in winter and sometimes low 90s in summer. I like them to experience the seasonal variations that their species would be adapted to dealing with in the wild.

This discussion always seems to gravitate toward talking about what night temps tortoises can survive. People will come on to the thread and relate stories about how cold they let their tortoises get and how they are fine. There is no doubt that tortoises can survive some pretty cold temperatures. Even tropical species like sulcatas can survive cold temps. But my question is always: What temps are optimal for a given species, vs. what temps are survivable. It is a tough question to debate. If I keep mine one way, and they all seem fine, but another guy keeps his differently and they all seem fine, who is "right"? How do we measure this? Are mine more "fine" than his? Or vice versa? What is his definition of "fine" vs. mine?

Speaking only about sulcatas and leopards, I kept them much cooler at night in years past, and they all survived and seemed fine. As I studied more and more about their lives in the wild, I decided I didn't think they should be so cool at night, and I made a change in how I housed and heated them at night. They had always been "fine" for all those cold years, but when I started keeping them warmer at night I saw a huge change for the better. Appetite and activity were much better. Growth and reproduction improved. I liked the results I was getting. Everyone I know who used to keep their sulcatas colder at night, but switches to warmer nights, loves the results. No one I've come across ever wants to go back to the cold way. The only people I hear saying that they think its fine to let them be cold are people who don't want to spend the time, money or effort to keep them warmer, and have no idea what the difference is because they've never tried it.

Speaking about russians and CA desert torts, I found a big difference in their behavior, appetite and overall health when I started keeping them a little warmer too. We tend to have large temp swings from day to night here. 80 degree sunny days, are frequently followed by nights in the low 40s to high 30s. My tortoises did okay in their shelters where night temps would drop into the 50s during these cold nights, but they were usually lethargic and slow to get started the next day, with low appetite. Too many cold nights in a row, and they would stop eating entirely. I'm talking about spring and fall, not winter when they want to hibernate. I started heating their night boxes a little bit, keeping temps in the low to mid 60s, instead of low 50s, and I saw a huge improvement in their behavior and appetite. They still got a night temp drop, just not as much of a drop, and they did "better".
 

Anyfoot

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Interesting.

So we know that weather stations don't give out the reading we tortoise enthusiasts require for babies, for example their humidity readings are air humidity reading which are probably way off the micro climate reading we are after for baby tortoises. What it does give us are the extreme temps that occurs within that region, so we can get an average temp to work with. As for humidity, is it safe to assume the higher readings that weather stations give out are a good starting point.
For example in Bahia(SA) during the day at this time of yr the air humidity is around 40% and at night 80/90%. We all know that the micro climates are going to be way above the 40% air humidity readings and I would have said 80% would have been a good starting point.

What I'm trying to work out is in most parts of the world there are higher temps and lower humidity in the day than at night according to weather station readings. But these readings are kind of irrelevant with our microclimates.
In temperate climates where there can be bigger swings in temps for longer periods it's a different ball game.
So assuming the micro climates are more stable than weather station readings, I mean it's not going to be 92f down in the undergrowth in deep deep shade in the day and equally probably doesn't drop to 75f at night. You would expect this micro climate to be let's say 80/85f constantly within a tropical climate. Obviously humidity is higher down in the undergrowth than air readings.

Its all coming back around to my obsession on how they grow. We've all established that warm and humid is the best climate for smooth growth, But fir example does a baby Leo venture out into the sun in the day when it's 95/100f and not even 19% humidity. (Look at Juba weather readings) If they do venture into this hot dry climate in the day, how long for, is it 1hr just to warm up,but do they need to warm up if micro climates are more constant anyway.
Maybe they do come out in day, but there's no growth whilst they are active and growth commences at night when at rest in the warm humid climate. Or maybe they just stay in the warm humid micro climate for months, years maybe, but then where's D3 come from, has to be diet at the earlier months, years.
 

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I don't know if we know when growth occurs. I don't know.

I'm reminded of a TTPG presentation where the speaker related his experience looking for cuora in the vietnamese jungle. He said it was so hot and humid at 6 feet off the ground where they were walking and standing that a person could barely breathe or move. Temps were near 100 degrees F. He really emphasized how stifling it was and that walking just a few feet made them fell like heat stroke was eminent. He got down on hands and knees and was searching through the under brush and it felt cooler. He put his thermometer down there in some of the thicker brush near the bases of the trees and found temps in the high 60s. How is that even possible? Daytime temps were near 100 and night temps were in the 80s. But he had pics of the digital readout on his thermometer...
 

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Could it be Precipitation(dew) from each morning keeping temps down at ground level.
 

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I don't think it is an issue of what part of the day growth is occurring most. It would make sense that when core body temp is close to optimal, and nutritious food has been consumed - that is when growth is occurring.

(Here's my current theory on this...) However, pyramiding is when the newly formed keratin that is being formed at the expanding growth seams is dried too much and cannot rehydrate. As it dries, keratin hardens and becomes stiff and non-permeable. We all see the new growth seams with our tortoises. The keratin there is softer. Next time you bathe your tortoise watch as the carapace dries on one with an active growth seam. You can actually see the scute dry off and the seam remain wetter longer. As this occurs, the seam will look much darker and visibly wetter than the rest of the scute. That new keratin acts differently. It takes on water more readily. In this stage, keratin swells with hydration. The growing seam needs to remain long enough in this state to allow that seam to fill in evenly for smooth growth. If it dries prematurely, the top of the keratin at the seam will no longer take on moisture when available and remain stiff. Additional swelling occurs only at the bottom of the seam and pushes downward. So the seam grows lower than the previous seam. = pyramiding.

Day time humidity is lower than night time because we always refer to 'relative' humidity. The warmer the air, the more moisture it can hold. So the same amount of water molecules present in the air will result in a higher relative humidity the lower the temperature. Once temperatures go low enough - you reach the "dew point". that is where the amount of water molecules in the air is the maximum amount air can hold at that temperature = 100% humidity. Dew will form as water precipitates from the air. Any surface that is just a tiny bit cooler than air temperature at this stage will become wet with "dew". That is why you see morning dew - the ground is slower to heat than the air as the sun comes up. The air temp is still at or near dew point, so the air releases water onto the cooler surface = dew. The more the temperature differential, the more "dew" and the farther from dew point (lower relative humidity) is required to still precipitate moisture from the air. A cold drink on the table forms moisture on the side of the glass even in very low humidity when the differential between glass temperature and air temperature is great. The insides of our tortoise enclosures form condensation as the air temperature of our enclosure is warmer than the glass window cooled by the room temperature.

In areas where tortoises live, and in times of the year when they are most active and growing, dew point is reached most every morning. With high humidity, that condensation effect occurs with small temperature differentials throughout most of the evening and mornings. So not only do our tortoise keep their shell moist burrowing in under brush, leaf litter, and into burrows, but they also emerge from these protected places and their shells are cooler than air temperature throughout the warmer parts of the day. So although relative humidity has dropped some (But not much in their part of the world) that differential between their shell temperature and air temperature will cause moisture to form on their shells. Keeping that new keratin layer hydrated. (As warm blooded animals, we never notice that effect ourselves. But an ectotherm lives with that temperature differential.) That is very different than the environment we provide for our tortoises in captivity. Unless we provide a humid chamber, our homes and areas most of us live are far too dry (relative humidity) and the air is indeed too desiccating on that keratin growth.

Just look at how your skin feels if you've ever visited the tropics. Our skin (keratin) does not even need lotion applied to keep it from getting dry and scaly looking! While at home, without lotion, I can start looking fairly reptilian!!

So I don't think we need to look at when growth occurs on a daily basis. Instead, it is that period when the new keratin expanding and we see active growth seams, when our tortoises are exposed to pyramiding. In captivity, that is year-round. In the wild, that is the times of year when the way they live in their environment takes care of hydration.
 

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Could it be Precipitation(dew) from each morning keeping temps down at ground level.

You mean in the tropical rain forest jungles of Vietnam? Its certainly wet down in the brush. I don't know how much evaporative cooling there would be with humidity already so high.

I'm reminded of a job I did in New Orleans in June a few years ago… Daytime highs were 100-105 night time lows were mid 90s. Fahrenheit. The lows. Mid 90s. Humidity was 95-100%. Anyway… We were filming nights and my dog had to wear a bunch of special effects make-up, so every night after filming I had to bathe him. One morning as the sun was coming up, I did his usual bath, dried him off and I draped the towel over a barbed wire fence to dry. Weather was sunny, 100+ degrees and no rain or clouds at all. We went back to the hotel and slept, then came back in the early evening for another night of filming. I went to retrieve the towel and it was still sopping wet after sitting in the sun all day. It was right where I left it and no one had touched it or gotten it wet. The water just couldn't evaporate out of the towel, even in full sun all day, because there was already so much water already in the air. I would imagine the air in the shadows of the canopy of the Vietnamese tropical rainforest would be even worse.
 

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When we go on holiday to Mainland Spain, Spanish islands or Greek islands during July August or September time its blazing hot 30/40c and dry during the day, when the sun goes down it cools to a 25/30c and you sweat like a pig. The humidity is off the scale, it's literally like sticking your head in the vivarium, harder to breath. Mind you mines probably exaggerated with beer :D.
Point is, even in the med it is super humid at night and up to sunrise. What I don't know is what is it like outside the 3 months I've mentioned.
 

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From what your both saying, night time lows are more important than we think, because the very nature of lower temps at night increase humidity as long as there is moisture in the air in the first place, this in turn creates dew droplets on the carapace.
 

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From what your both saying, night time lows are more important than we think, because the very nature of lower temps at night increase humidity as long as there is moisture in the air in the first place, this in turn creates dew droplets on the carapace.
In my enclosures, the daytime temperature creeps into the 90°'s with the ballasts from the fluorescents and the basking floods heating the enclosure. At night, with the lights off the temp drops to 80° where the CHE holds it. The humidity then goes down to 80% daytime, and up to 95% at night as the temperature "cools". However, since our enclosures keep the tortoise at a stable temperature equal to the enclosure temperature, the effects I am referring to above are not in play. So I don't feel a night drop in our enclosures is at all that necessary. Because of the uniform temperatures we are providing, uniform, high humidity is important.

"In the wild" is a different story. The night drop to dew point is a way tortoises' shells can remain rehydrated with the drier daytimes. We work with a totally different set up parameters in our enclosures.

And it is not just the dew formation. The high humidity that is maintained while the tortoise is growing and "exposed" is important. Without visible drops of dew forming, the hydration effect still can be great as a cooler shell absorbs some moisture from the air. A tortoise emerging from hiding in the morning will be colder than air temperature. My platynota are most active at sunset and a few hours beyond. They retreat to their hides with their shells cooler than the air temps of their hides. In the wild, these are mechanisms that creates conditions that simply looking at temperatures and humidity from a weather station does not show. Nor does simply throwing a thermometer or hygrometer in a burrow or pallet show results that take these factors into account.
 

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Mark.

I agree weather stations are at best a starting point, and are just not a true reflection of our baby tortoise needs.
Take your point with night lows, our entire enclosures need to be that point where dew develops, hence, high humidity.

I've plenty to think about again.

Mark. There's one thing I need to get straight, and that is how dew comes about. I thought dew formed when 2 object of different temps clashed. So for example my warm tortoise wanders around its enclosure at 91f, when it goes to sleep in foliage at 79f it gradually cools down to 79f. The nightime low kicks in to 82f which is still higher than 79f where the tort is sat in foliage. So as 82f air meets 79f foliage there is Dew. My torts come out of the foliage with droplets on the carapace. That's either because the temp difference between air and foliage(and tort) is keeping the foliage moist with dew or it's because my foliage is still moist from when I first set it up 2 wks ago. I'm not spraying the foliage. Either my foliage will dry out or night time lows will keep topping it up with dew.
 

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Mark.

I agree weather stations are at best a starting point, and are just not a true reflection of our baby tortoise needs.
Take your point with night lows, our entire enclosures need to be that point where dew develops, hence, high humidity.

I've plenty to think about again.

Mark. There's one thing I need to get straight, and that is how dew comes about. I thought dew formed when 2 object of different temps clashed. So for example my warm tortoise wanders around its enclosure at 91f, when it goes to sleep in foliage at 79f it gradually cools down to 79f. The nightime low kicks in to 82f which is still higher than 79f where the tort is sat in foliage. So as 82f air meets 79f foliage there is Dew. My torts come out of the foliage with droplets on the carapace. That's either because the temp difference between air and foliage(and tort) is keeping the foliage moist with dew or it's because my foliage is still moist from when I first set it up 2 wks ago. I'm not spraying the foliage. Either my foliage will dry out or night time lows will keep topping it up with dew.

Are any of you fellows familiar with the 2016 study by Heinrich and Heinrich published in the Journal of Exotic Pet Medicine which states that a daily heating and cooling cycle is required by chelonians to prevent pyramiding? Here is the final part of their article:

"CONCLUSION Chelonians are dependent on heating and cooling cycles for optimal metabolism and subsequent growth. Application of nocturnal heat increases growth rate and CSP incaptive-raised leopard and spurred tortoises. When designing captive environments, one must consider various species’ natural and phylogenetic histories. Although all nutritional and environmental variables need to be evaluated, heat cycles are of paramount importance for proper growth rate and shell formation. CSP may be reduced and ultimately eliminated as evolutionary requirements of a specific species are applied I in a captive setting."

Note that CSP above means Carapacial Scute Pyramiding.

Anyone wanting to read the entire study may email me for a copy of the article. [email protected]
 

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Are any of you fellows familiar with the 2016 study by Heinrich and Heinrich published in the Journal of Exotic Pet Medicine which states that a daily heating and cooling cycle is required by chelonians to prevent pyramiding? Here is the final part of their article:

"CONCLUSION Chelonians are dependent on heating and cooling cycles for optimal metabolism and subsequent growth. Application of nocturnal heat increases growth rate and CSP incaptive-raised leopard and spurred tortoises. When designing captive environments, one must consider various species’ natural and phylogenetic histories. Although all nutritional and environmental variables need to be evaluated, heat cycles are of paramount importance for proper growth rate and shell formation. CSP may be reduced and ultimately eliminated as evolutionary requirements of a specific species are applied I in a captive setting."

Note that CSP above means Carapacial Scute Pyramiding.

Anyone wanting to read the entire study may email me for a copy of the article. [email protected]
Thanks for the input here, Bill. I really value any experience and learnings you can share.

Yes, I am very familiar with this study and have studied it and their techniques quite a bit in the past. I do not agree with their conclusions and their research has several variables that were absolutely not controlled in the way they set up their experiment and study. One of the biggest is what I mention in the post above - that a drop in temperature automatically brings a rise in relative humidity. They kept all tortoises in an open top enclosure. The heating provided for the "night heat" group was therefore rather desiccating all night, while the "night drop" group had no desiccating IR exposure all night and an increase in humidity. They do not account for that, nor even seem aware of that in their study. Their results did not eliminate pyramiding. All tortoises pyramided in both groups. The night drop groups just experienced a bit less pyramiding. In my opinion, that was a result of the above effects. Their conclusion is pure conjecture and none of the results of their experiment support that conclusion.

Additionally, we/I have plenty of cases of smooth tortoises grown without night drop, but consistent humidity. They did not grow any smooth tortoises with their techniques. I was interested because it was a similar experiment to what I did with several of my sulcata groups about 20 years ago trying to figure out this pyramiding thing.
 

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Are any of you fellows familiar with the 2016 study by Heinrich and Heinrich published in the Journal of Exotic Pet Medicine which states that a daily heating and cooling cycle is required by chelonians to prevent pyramiding? Here is the final part of their article:

"CONCLUSION Chelonians are dependent on heating and cooling cycles for optimal metabolism and subsequent growth. Application of nocturnal heat increases growth rate and CSP incaptive-raised leopard and spurred tortoises. When designing captive environments, one must consider various species’ natural and phylogenetic histories. Although all nutritional and environmental variables need to be evaluated, heat cycles are of paramount importance for proper growth rate and shell formation. CSP may be reduced and ultimately eliminated as evolutionary requirements of a specific species are applied I in a captive setting."

Note that CSP above means Carapacial Scute Pyramiding.

Anyone wanting to read the entire study may email me for a copy of the article. [email protected]

Like Mark, I am also appreciative of every post you take the time to type up here. I read all of them with great interest.

I am not familiar with that study, but from reading what you and Mark have written about it, I see the same problem with this study as I do with so many others and with the people who argue against the style of tropical tortoise keeping that I advocate. My first hand results completely refute their conclusions and assertions, and so do the results of all the people all over the world who are duplicating this grand experiment. Also, the experiment in your post, and the people who argue these points with me, have never raised a tortoise the way I'm raising them, yet I have raised tortoises many times the way "they" typically advocate. I know what the results will be with "their" method, but they don't know what the results will be with "my" method because they have never done it. Makes it difficult to have a meaningful discussion when one party is completely ignorant of half the material being discussed.
 

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Nighttime temperature lows/drops are a natural thing in any wild environment and with greater or lesser fluctuations at different points in a year for the same geographic area. It has benefits already mentioned. If eliminated, there often needs to be compensation in terms of maintaining smoother growth. Since the animals evolved over ages in that environmental situation, there may be other benefits aside from cosmetic effects and those hypothetical benefits could be lost if eliminating the drops (we do not know what we do not know).

With babies of jungle and near-jungle species, I tend to avoid real night drops for the first year or two. Of course, by the second year (for me), they are subadults. For adults of jungle and near-jungle species, I let them experience a night drop for practical reasons.

For more temperate species, a night drop is the way I have taken and would take it.

You are not necessarily incorrect to avoid a night drop. You are not necessarily correct to avoid a night drop.

As for lows in terms of tolerance, this will depend on a bunch of things. Species. Subspecies or locality. History of exposures allowed (huge, huge factor). There are few good reasons to explore an animal's limits of tolerance. That is more for knowledge-gathering than anything of benefit to the animal, although it is valuable to other animals in future applications or considerations. However, the rise of over-coddled animals is something interesting. Animals which experience an accidental 50-60-degree night and suddenly are weakened and experience rapid illness are a shame to see. Animals which are allowed to experience gradual exposures tend not to react like that. There is a tempering process that can be achieved if done with some intelligence (or luck for some that do not plan it, but that does not necessarily end well often). Hardened animals are more safe when an unforeseen event occurs. You have no express need to explore this, but there is a benefit. It is also cool to observe it. An excellent example that has been showcased here is Len's male sulcata (Walker). I have countless personal examples. The principles apply to any species of tortoise, although the extent varies with species and individual. It is not all-or-nothing.
 

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Nighttime temperature lows/drops are a natural thing in any wild environment .

@Baoh I do enjoy your posts and try to read every one I see to try to pick up and learn something. I value your expertise and experience.

I do have a question about the part of your post you started with and I included above. That is what I feel is misleading. It is so often, as here, simply stated as a simple fact and then used to justify night drops. Where I see this the most is with sulcatas to justify not, or minimally heating them at night in captivity.

Do you have some basis for fact that I am unaware of? My point in the posts above is that tortoises do not live where weather stations are positioned - above the ground. In the particular case of the sulcata, they live in burrows that are normally 2 - 8 meters deep. There are no night drops there. All the studies on ground temperatures show variations in daily temperatures become almost negligible at 0.25 m and below. I really find value in this discussion because I do believe it is a root of a lot of older misconceptions about how to keep tortoises.

To suppory my point, I will show just one of the dozens of charts I have on actual data for daily temperature values at depth. This is from a study done on the Island of Cyprus. It looks at one day that went from an air temperature of a low of 14°C (57°F) to a high of 32.5°C (90°F). So a mild day in the terms of our sulcatas but a temperature swing of comparable value. At 4" deep the temperature pretty much followed the air temperature with a lag of a few hours. That is in the open, unshaded soil. Not under a bush or any cover. However, even there, at 0.25 m (10") deep, the temperature only varied over the whole day from 22°C (71.5°F) to a high of 23.5°C (74.3°F) At a depth of just 1 meter, the variation over the course of the day is well under 1°C

Temp Cyprus over 24 hours.jpg
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And the temperature at depth always stays within a few degrees of the daily average temperature. In Cyprus this day it was 22°C (71.6°F) If we look at average temperatures in the Sudan, for example, where some of your tortoises come from, we see the following ranges year-round if we look at data from Galgani, Sudan which is near some of the remaining G sulcata populations in the wild:

temp Avgs Galgani Sudan.jpg

So in their wild habitat, overnight low average never dips below 72°F throughout the year, and the daily average temperature (which ground temps follow) never dips below 85°F all year.

From this I can conclude pretty reasonably that retreating to a burrow, a wild sulcata never experiences a nightly temperature drop, and never endures temperatures below 80°F in their native range.
 

Baoh

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Do you have some basis for fact that I am unaware of?

Well, there were all of the times I visited areas where I have found a number of species in situ and where I found them during the day was of a temperature higher than where I found them at night. I have found tortoises in Europe, Central/South America, and Asia. The US, too, if we count Gopherus in this. I have yet to visit a place where the nighttime temperature of the tortoise at an activity nadir was equal to its daytime temperature at its activity apex unless it was completely buried for brumation.

In the particular case of the sulcata, they live in burrows that are normally 2 - 8 meters deep. There are no night drops there. All the studies on ground temperatures show variations in daily temperatures become almost negligible at 0.25 m and below.

Would you mind linking me to a study by an actual researcher that has measured sulcata burrow temperatures and showed zero delta between diurnal apex and nocturnal nadir with statistically significant data sampling? I assume, for your position, that you would use that kind of data. Were the studies you are referencing based on probes inserted into the ground and allowed to equilibrate while buried with substrate making contact on all sides or in an otherwise enclosed space (to know the ground temperatures since you mentioned ground temperatures)? Or were the studies done in open-air sulcata burrows? My sulcatas do not bury themselves in the ground material when they retire to their burrows excavated from the ground material, so a buried probe lacks equivalence to an unburied sulcata and that is only in the context of the burrow.

When my sulcatas reside in burrows, they do not reside within them for 24 hours per day. If mine only lived in their burrows and never emerged for active periods, I would assume there was something wrong with them. When they are out and active, their burrow temperature is not the daily high temperature that the animals experience. My burrows are around two feet wide and air flows into and out of them. There is even a low howl like a seashell when the wind really picks up before or during storms. That the air is warmer in the day and cooler in the night is sped up some when wind is higher. Like a cave, the temperatures are muted, but have fluctuations. It is a tube. Not a capsule. My sulcata burrows experience daily highs and lows on a more narrow range of temperatures than the surface highs and lows, but my sulcata tortoises themselves are exposed outside of the burrow to highs much higher than the lows they are exposed to within the burrow at the nighttime low. But again, my sulcatas do not sit in their burrows for 24 hours per day, so I would not be one to use the burrow temperature range to extrapolate to the animal's temperature range. Nor would I use data from a buried probe to speak for a burrow experiencing air exchange because I would not want to come across as intellectually dishonest on the matter. The burrow temps have a delta that is greater than zero. The animals are exposed to a delta that is much greater still compared to their burrows. I am not breeding and raising burrows. I am breeding and raising sulcatas.

To suppory my point, I will show just one of the dozens of charts I have on actual data for daily temperature values at depth. This is from a study done on the Island of Cyprus. It looks at one day that went from an air temperature of a low of 14°C (57°F) to a high of 32.5°C (90°F). So a mild day in the terms of our sulcatas but a temperature swing of comparable value. At 4" deep the temperature pretty much followed the air temperature with a lag of a few hours. That is in the open, unshaded soil. Not under a bush or any cover. However, even there, at 0.25 m (10") deep, the temperature only varied over the whole day from 22°C (71.5°F) to a high of 23.5°C (74.3°F) At a depth of just 1 meter, the variation over the course of the day is well under 1°C

Does this study's methodology have the probe placement performed in a sulcata burrow? Or is it a buried probe? If it is a buried probe and the species to be discussed are not buried beneath substrate to that depth, how does it support your point? Speaking of Cyprus (and Greece; I have been to both), when I have been there and observed the multiple species of tortoises in situ, their shells were rather warm to the touch in the daytime while active and somewhat cool to the touch at night while tucked into underbrush. Some with condensate on their shells during the early mornings at daybreak. Even going by my hand, that does not represent a delta of zero. These were primarily summertime visits. Spring and autumn seasonal variations combined with basking behaviors could make for an even larger delta for the animal's temperature within a day. In Greece, this involved a variety of terrains. Mountains. Valleys. Agriculturally developed areas. Undeveloped chaparral-like scrublands. Pine forests. Deciduous forests with springs or rivers (both seasonal and persistent). Three species in the Testudo genus in aggregate when dealing with exeriences combined from both countries.

And the temperature at depth always stays within a few degrees of the daily average temperature.

With what probe placement methodology? Buried or with access to direct air exchange? If with access to direct air exchange, over what dimensions?

So in their wild habitat, overnight low average never dips below 72°F throughout the year, and the daily average temperature (which ground temps follow) never dips below 85°F all year.

From this I can conclude pretty reasonably that retreating to a burrow, a wild sulcata never experiences a nightly temperature drop, and never endures temperatures below 80°F in their native range.

Even if you are talking about buried (substrate-encased) probes (apples) and not sulcata burrows (oranges) with air exchange or the actual sulcata tortoises (pears?) themselves, that is not the full range of exposures the animal experiences within its full day. You are taking data twice removed and making a conclusion based on measurements that were not taken of the very thing you are concluding on. A buried probe is not a burrow space. A burrow space is not a tortoise. A tortoise at night in a burrow is not the same temperature as it is during the day outside of that burrow. If I buried a tortoise completely at a particular depth to replicate a probe reading, that in no way represents what the tortoise would experience without me doing so.

And that is only speaking to sulcata tortoises since you decided to focus on that species. Other species experience a night drop as well. Their lowest resting temperatures at night are not the same as their highest active temperatures during the day unless you want to somehow reasonably conclude otherwise with measurements taken of the tortoises themselves. That delta or difference is the night drop. A leopard tortoise under the cover of brush and grass during the lowest temperature of a night is experiencing a night drop relative to if it stayed in that position while in the shade of the same brush and grass during the highest temperature of that day (which is still not the highest temperature it experiences while active during the day with direct exposure to sunlight). When a South African pardalis is observed having frost on its shell before dawn breaks, that is probably at a lower temperature than what the animal experiences at noon on the same day. That, too, is a night drop. When I have found redfoot and yellow foot tortoises during the day and then again at night, the temperatures were not the same at the level of the tortoises at those different times of day. Also a night drop.

As before.

Nighttime temperature lows/drops are a natural thing in any wild environment and with greater or lesser fluctuations at different points in a year for the same geographic area.

At least for tortoises not brumating. Not talking about buried probes that do not represent active tortoises in a day/night cycle.
 
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