How much UVB exposure?

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How much UVB exposure?

Postby Paul Kingtiger » Fri Aug 12, 2011 6:06 pm

Hello,
My recent rescue Russian, Tippy is doing very well, she loves to explore and especially climb. She's an indoor tortoise until at least next summer although she gets supervised trips outdoors. Her normal home is a 5'x3' tortoise table, but she also gets to explore around the house when I'm home, which she loves! My question is how much UVB exposure does she need each day, because when she's out of the table she isn't getting any. The table has a 160w powersun MVL and a UVB striplight which together give good gradient and exposure (97 hot end - 70 cold) and she seems to spend a good amount of time in various parts of the table.

She was rescued from a 20inch x 10inch tank so I'm eager to give her as much exercise as I can.
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Re: How much UVB exposure?

Postby Tortoise Trust » Fri Aug 12, 2011 6:25 pm

Paul Kingtiger wrote:My question is how much UVB exposure does she need each day.


Simple question. Incredibly complex answer.

First, this species spends around 8-9 months of the year either estivating or brumating (hibernating). Clearly, in captivity, activity patterns and growth rates are different.

The whole issue of how much UV-B they:

a) Need
b) Get in the wild

is... yes.. incredibly complex. It varies seasonally from day to day. Right now here (T. g. graeca in Southern Spain) they are mostly buried down, getting none... the LEVELS out there though, are very high (+300 uW/sq cm). A few weeks ago, they were emerging just after dawn, and only again after sundown (low levels of UVB) heat being the prohibiting factor..

All the evidence from other animals is that they do not need a lot. Humans can do quite well on just a few minutes exposure at modest levels, for example.

In captivity, you are really looking for an acceptable, functional, "average" figure, which going by all the evidence I have so far, is likely to be in the 150-180 uW/sq cm range for 30-40 minutes a day at basking temperatures in the 30-34C range. Basking temperatures are critical, because temperature is part of the process in converting UVB to usable vitamin D3 by activation of sterols in the skin.
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Re: How much UVB exposure?

Postby Paul Kingtiger » Fri Aug 12, 2011 9:08 pm

That's less time than I thought. Tippy will bask right under the lamp then after a while move further away but still under it, so I'm reasonably happy that she is regulating her own temperature effectively. The UVB output of my Powersun is less that you're recommending although the lamp is on for 12 hours a day. She's very active though in the table and outside it. In fact on the floor she'll be on the move for a few hours before she gets bored and has a sleep.

My biggest problem with taking her outside is she eats everything and gets no exercise as long as there's food within reach. Hopefully by next summer I'll have an outdoor enclosure set up where she can get some proper sun.
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Re: How much UVB exposure?

Postby JonathanOz » Fri Aug 12, 2011 10:56 pm

Andy does that mean that it migth not be a good thing to be providing UVB for hours every day, even if the level was a bit lower such as 130 uW/cm2?

I could alter my set-up to provide heat by halogen lamps most of the day and only use the UVB lamps for part of the time.
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Re: How much UVB exposure?

Postby Rom » Sat Aug 13, 2011 12:04 am

Tortoise Trust wrote:
Paul Kingtiger wrote:In captivity, you are really looking for an acceptable, functional, "average" figure, which going by all the evidence I have so far, is likely to be in the 150-180 uW/sq cm range for 30-40 minutes a day at basking temperatures in the 30-34C range. Basking temperatures are critical, because temperature is part of the process in converting UVB to usable vitamin D3 by activation of sterols in the skin.


Guys this is really an important statement made by specialists living and studying in the enviroment and understanding the measurement and experimental methods that go with the work.

Looking at Frances Baines' figures it stacks up with a UK reading in spring and confirms that our summer uv levels are more than good enough .

Regrettably you lucky buggers have a bit more heat than we do and thats is so important.

http://www.uvguide.co.uk/uvinnature.htm

Thank you for posting this.

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Re: How much UVB exposure?

Postby Tortoise Trust » Sat Aug 13, 2011 1:58 am

JonathanOz wrote:Andy does that mean that it migth not be a good thing to be providing UVB for hours every day, even if the level was a bit lower such as 130 uW/cm2?


It is very difficult "translating" what is experienced in nature to a totally artificial environment. In nature, the UVB levels change constantly, literally from minute to minute as the earth rotates, moisture levels in the air change, clouds pass over, and as the tortoise moves around... out in full sun... back under vegetation cover (full or partial). The tortoises behaviour is itself is highly complex, being regulated by conflicting pressures to warm up and cool off (thermoregulation), and desire for certain activities, feeding, mating vs. the need for predator avoidance. Their behaviour in the wild is very different from that of a typical captive animal. There are a great many days in the wild where tortoises are not active at all.In captivity, people expect to see them up and about, and feeding, virtually daily, from emergence in spring right through to autumn, and often beyond...

So, it is very challenging to interpret what goes on in the wild in the Mediterranean to a completely unnatural and artificial existence in Northern Europe.

In terms of gross UV-B levels, I have recorded tortoises in Spring basking for extended periods in open conditions with levels below 40uw/ Sq. cm. and as high as 280 uw/Sq. cm.

The extended periods are usually in cool weather. In late spring and summer they do not need to bask for long at all to raise their temperatures to the desired level. Juveniles and adults also bask for entirely different periods even in identical conditions due to body size considerations (thermal inertia).

High temperatures as a limiting factor on activity:

viewtopic.php?f=5&t=6475

So, you can see the problem when questions such as "how long do I turn on my UV-B lamp for" arise! Not only is the lamp not the sun (its lighting spectrum is entirely different) and its pattern of infra-red (heat) radiation is also entirely different, but the animal is also behaving entirely differently.....

The only way to really know if an artificial UVB lighting system and habitat are providing what is required would be to run some blood samples for calcidiol levels, then to compare that with samples from wild specimens to give an acceptable range. Obtaining that data from wild T. graeca is something we have planned for next year. This year we have been too occupied with behavioural aspects (which is extremely time consuming).

At risk of considerable oversimplification, all our observations to date support the contention that T. g. graeca does not normally spend huge amounts of time basking at very high UVB levels in nature, at least at the altitudes of the sites we have studied. High altitude tortoises may spend longer, because it is a) cooler and b) the levels are already higher at altitude.

Some photos of one study site and measurement methods:

viewtopic.php?f=3&t=5363&p=51478&hilit=uvb#p51478

My own view is that based on current knowledge, I feel it advisable to provide artificial UVB levels in the range I suggest, ie., using lamps capable of producing around 180 uW/ Sq. cm at ground level, and ensuring that a gradient and full retreat is available...I also feel that as much outdoor time as possible should be provided. As Rom states, even in the UK quite acceptable levels are often achieved, and unlike here, they can spend longer out in that as they are not going to overheat as readily...conversely, their efficiency at using that UVB may be reduced, however, for the same reason (achieving temperatures required for effective conversion).

As you can see, this is a complex area. We are continuing to take a lot of measurements and we are looking at UVB levels combined with thermoregulation and other behavioural factors. We need more data, and some blood analyses will be very useful. A lot more work to be done in this area.
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Re: How much UVB exposure?

Postby JonathanOz » Sat Aug 13, 2011 7:08 pm

Thanks that is really helpful and I need to take some time to read it through to get a better understanding. My hermanns are mainly 'outside' at the moment - i.e. in a plexiglass colframe with halogen baksing lamp and a fully outside planted area. This does give them lots of options and I try not to interfere.

I also have some yearlings which are mainly indoors in totally artificial conditions and I can get levels up to 180uW/cm2 with a vitalux lamp or the 160W MegaRay but I've been providing less intensity than that. With some adjustments I should be able to have 180uW/cm2 of UVB available part of the time and lower levels most of the time. I do get the small ones outside some of the time.
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Re: How much UVB exposure?

Postby Tortoise Trust » Sun Aug 14, 2011 7:31 am

A bit more background on methodology...

For a long time now we have been recording both direct and dappled shade UVB and correlating this with tortoise behaviour. For example:

Image

A lot of the data out there on this subject is extremely misleading.... precisely because it is NOT correlated with wild behaviour, and hence actual exposure time/intensity. For example, this is a pair of readings I took yesterday at mid-day:

Image
Image

Very impressive... lots of UVB! However... absolutely NO tortoises are out in it. None. Zero. They never are. Why? Here's why:

Image

They are completely hidden. Estivating. So referencing figures of over 400 uw/sq cm. in T. g. graeca habitat and concluding from this that they need similar levels in captivity would be barking up completely the wrong tree...

Here's a little graph I did one day last September, during tortoise activity:

Image

Again, important to note tortoises were only out and receiving UVB for a short time that day... not ALL day. The lesson here is to be very wary of figures based on maps or simple UVB levels in a particular zone.... because unless the data is matched to activity patterns is is virtually without meaning as far as husbandry is concerned.
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Re: How much UVB exposure?

Postby Rom » Sun Aug 14, 2011 8:50 am

I wish we had a similar simple data set for turtles in the Carolinas or New England.

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Re: How much UVB exposure?

Postby Tortoise Trust » Sun Aug 14, 2011 9:52 am

It is not hard (technically) to get this kind of data, Rom... but it is very time-consuming and slow work. Unlike temperature/humidity data, you have to record it all manually, and you need to be 'on the spot' to do the correlations with behaviour. All you need are some UVB meters, a notepad, a thermometer or two, and a pair of binoculars so you can observe behaviour without distracting the animal.

In the US, maybe a collaborator on the spot might be feasible?

I'm hoping next year we can begin to gather a bit of similar data on our local Mauremys populations. From what I've seen personally of turtle ponds in New England, there is a really big range, from completely open and unshaded to very heavily shaded, quite "dingy" examples... do they compensate by basking for longer in the latter? It would be interesting to know!
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