A common question that crops up among herpetoculturalists who keep Uroplatus is how much UV they need. This is an important question, because UV, especially UV-B, can be critical to reptiles (and other animals) because it is involved in the pathway that produces vitamin D3 and allows for calcium to be absorbed by the body. But it is not really clear how this works in nocturnal reptiles. In Uroplatus we have the interesting case that the geckos, although active at night, sleep “out in the open,” as it were—at least the bark-mimicking geckos tend to sleep on tree trunks and there is the possibility that these trunks are exposed to sunshine, giving the gecko a chance to bask. If this is the case, then in the captive husbandry of the geckos the opportunity to bask in UV-rich light would need to be provided. Over three years of field research, we tried to gather data on the UV exposure of sleeping Uroplatus during the day, using a Solarmeter 6.2 in the rainforests of Madagascar.

The following is an account of attempts to make measurements in Montagne d’Ambre in 2017–2018, Marojejy in 2016, and in a high-altitude forest near Bealanana in northern Madagascar in 2015–16. These observations are therefore directly relevant to Uroplatus sikorae, U. sameiti, U. giganteus, U. aff. henkeli Ca11, U. ebenaui, U. finiavana, U. fotsivava, U. lineatus, and U. alluaudi (and a few undescribed species that are not yet public knowledge), but they can be generalised over all Uroplatus species with the correct level of caution. See below.

First of all, there were several major challenges in assessing the UV exposure of Uroplatus:

1. We have had a lot of trouble with the Solarmeter readings because they vary dramatically within centimetre distances. How do you standardise the measurements? Over the three expeditions we conducted, we did not have any success in finding a way to take these measurements in a standardized way, in part because it was difficult to integrate the Solarmeter usage into the daily regime, and in consequence it was not used as often as could be desired, and never in a standardized way. We tried in 2017–2018 to have a student collect the data over transects whilst looking for chameleons, but in the end it was too tedious, unreliable, and time-consuming to be continued. Not to mention rainy!
2. Over the last three expeditions, cumulatively half a year in the forest, we have found a grand total of maybe three Uroplatus during the day, and in none of those instances was the solarmeter to hand. Measurements taken in the proximity of geckos found during the day are out of the question in terms of usefulness, because they simply are not numerous enough to be statistically useful.
3. There are dramatic differences to be accounted for depending on the perching habits of the species, making generalisations difficult. Bark-mimic species (henkeli complex, giganteus, fimbriatus, sikorae/sameiti complex, and lineatus, but also to a lesser extent alluaudi, guentheri, peitschmanni, and malahelo) may at times be exposed to full sun for brief moments, but probably not for long. The angle at which light hits them is always steep, and typically they are experiencing diffuse light because they are on the trunks of trees, where there is the most shade. By contrast, leaf-mimic species tend to be mostly or completely sheltered during the day, exposing only part of their bodies at all to the light, and certainly not basking. So what is the relevance of environmental UVB readings at all to these animals, which are generally hidden from the light?
4. Light in the forest varies dramatically (1) by time of day, (2) by position, (3) by canopy type, (4) by microhabitat, (5) by altitude, and most strongly (6) by season. We conduct fieldwork during the rainy season, where light is lowest and rainfall is heaviest, and where in a single day we have massive swings from dark-as-night cloud cover to bright direct sunlight to diffuse light with or without rain. Needless to say, readings at a single moment in the day are not helpful, because we need an impression of the average exposure of the species to advise husbandry.

Given all of these caveats, you will hopefully understand why this report is fragmentary and perhaps not obviously useful. But it perhaps contains relevant notes on the ecology of species to make informed decisions about using UV light in your Uroplatus care.

UVB levels within the forest typically range from 0 to 15 µW/cm2. In dense primary forest, usually we are getting 0-2 µW/cm2, with upwards of 5 in more open areas, and sometimes up to 15 µW/cm2 in patches where the sun is shining at that very moment. In more open forests, the maximum we have seen is up to 30 µW/cm2, but sometimes we can get as much as 50 µW/cm2 in really blazing sun (probably more frequent in the dry season!). Outside the forest and on its edge we are getting triple digits sometimes, but this is really in areas where Uroplatus basically never occur (maybe useful if anyone keeps edge-loving chameleons though, especially Furcifer pardalis, F. petteri, and Calumma nasutum group species).

All in all,  the maximum a rainforest Uroplatus is probably ever exposed to is probably 30 µW/cm2, and as mentioned above, this is probably more than a leaf-mimic species ever experiences. This is not an average value, however. As these geckos really do not seem to bask, and rather are hit coincidentally by light as the sun moves across the sky, the average exposure of any Uroplatus is probably between 8 and 10 µW/cm2, and lower in leaf-mimics. Thinking about the drier forest Uroplatus, where the canopy is less dense, we can raise these numbers a bit and say 10-15 µW/cm2 is a likely good average (again lower in leaf-mimics from drier forest, so U. malama and U. ebenaui).

Bear in mind that altitude also plays a big role: lower altitudes have less cloud cover, and typically more bright-sun-days per year than higher altitudes. So for example, U. ebenaui and U. finiavana may both occur in Montagne d’Ambre, but the latter occurs at higher altitudes than the former, and in more dense forest, and as a result, it must receive considerably less UV exposure. Fortunately, altitude and forest-type correlate rather strongly, so as long as you adjust UV levels for one or the other, you should come out okay.

Uroplatus pietschmanni (and possibly U. alluaudi) is probably exceptional, because it is a high-canopy species and as such probably has higher UV exposure than its relatives. Increasing by one or two µW/cm2 would probably cover this difference though. Uroplatus lineatus is also exceptional because bamboo forest has higher light levels than deciduous or rainforest. As such, it may be advisable to keep U. lineatus with higher light levels in general, and slightly higher UV levels than e.g. U. giganteus, which occurs in the rainforests beside the bamboo forest of U. lineatus.

Bear in mind when thinking about your husbandry that the weather is constantly changing in the forest. Clouds make UVB exposure swing massively. Replicates of natural environments in little boxes cannot mimic this effect, so it is safer to go with a lower-side-of-average value, rather than go straight for the high values of UV exposure. On the other hand, it would not be unreasonable to treat leaf- and bark-mimic Uroplatus from the same location with the same exposure, and simply provide more shelter opportunities for leaf-mimics… This would be more representative of their natural conditions. This is for the keeper to decide.

So far, the information from field observations is fragmentary and limited. Many factors could change the meaning of what we have observed so far; seasonal changes may vary exposure dramatically, these geckos may be basking more or less than we imagine, and they may be more sensitive to UV levels than diurnal lizards. Remember that no measurements from directly beside resting Uroplatus have yet been obtained, and these will be a critical step in informing decisions further. As such, this is still very much up to the keepers to decide.

As a parting note, consider that UV exposure may not be necessary for the survival of Uroplatus in captivity, but it may still be highly beneficial for them. In a large enclosure, providing a moderately weak UV light is unlikely to do damage.