The question that has constantly vexed us Jackson's keepers....
If Jackson's Chameleons are so sensitive to conditions, why are they all over Hawaii, constantly rumored to be in California, and, potentially, being farm raised somewhere on the US mainland? And if they are so good at being a reptile weed why do we, in captivity, have so many problems with Temporal Gland Infections once the temperature creeps to the upper 80s and why do broods of babies drop dead at the three month point? I have struggled to answer these questions. I'll share where I am from my personal experience and research and you can take away anything that makes sense.
From my working with caging, I know there is a big difference between living in the wild with numerous microclimates to choose from and being restricted to a 2x2x4 space. The smaller the cage the more ideal the conditions need to be. By having a heavily planted 4' x 4' x 7' cage on natural earth, nestled against a large bush on one side and a wall on the other side I was able to keep Jackson's and quadricornis outdoors through a California summer that spiked over 100 degree weather at times. I am sure they would not have lasted for weeks at the temperature, but I do know that they would have died in a day if they were in a smaller, enclosed cage. During these high temperature times they would hide down in the shaded low areas near the soil. I stuck my hand where they were roosting and was surprised at how cool it was. So, even though the weather app was telling me it was 100+ F, they were not hanging out in 100+ temperatures. All well and good to explain how they can survive the higher-than-caresheet temperatures, but it is a whole lot harder to find a micro-climate that gives a chameleon a colder temperature than shows on the weather station. So why do we say they need the nighttime drop?
And for nighttime drop information I can only speak for my approach. Other people will have different reasons for what they say. When i was determining what nighttime drop to put on my caresheets I had to talk with breeders that have not had baby die-off at 3 months old. Not everyone has their Jackson's chameleons babies die at three months old, but it is common enough that a number of us breeders have four months as our general rule for sending babies to a new home. The common thread amongst the breeders that did not experience the die off was a combination of separating babies and a significant nighttime drop. The more cohabitation and the warmer the nights the more likely the babies would die off. So, for me, placing urgency on nighttime drops originates in the very murky reports back from successful and unsuccessful breeders (including myself). The reason why this is still a gray area is that the effects of both cohabitation and warm nights are cumulative and don't necessarily show until they add up and go over a threshold. So the damage a week of warm nights can cause will subside if the nighttime temperatures drop the next week. And then the stress count increases or decreases based on the cohabitation situation. So it would take a great amount of work to parse these things out and isolate the magnitude of stress each component causes. Though the biggest unanswered question is how much of a drop is necessary and this test requires controllable nighttime temperatures over a long period of time across multiple broods. I fantasize about having a facility where I can have ten groups at different nighttime drops and just cycle groups of babies through to measure the effect. But that is beyond what I am able to do right now! So, for me, the urgency for a nighttime drop is more a response to how they are reacting to captivity than it is taking it from wild data. And each chameleon species responds to conditions outside the ideal differently. Go hotter than ideal? Jackson's Chameleons die and Veiled Chameleons just go into egg overproduction. So, even though Veiled and Jackson's come from roughly the same altitude and montane conditions, we don't have this constant stress about nighttime drops for Veileds. (Though I recommend it to give them good sleep too)
Because of Hawaii, I constantly have people challenge the temperatures on my Jackson's caresheets that have mild day temperatures and a nighttime drop. My response is that 1) chameleons are not hanging out at the temperatures showing at the weather station, 2) The smaller the cage the more ideal the conditions need to be, 3) over discussions amongst breeders that have healthy chameleons, they consider a nighttime drop an important part of their success, 4) As a breeder/keeper of many jackson's I know when I need to be much more vigilant for temporal gland infections and other bacterial nastiness. And that is when the temperatures get warm. Do we know it has to be a 10 degree drop? 15 degree drop? No. We do not know this. And we do not know at what point the body doesn't consider it a nighttime drop. I strongly suspect it is all on a sliding scale just like for us. We don't get a good night's sleep and we are cranky. another bad night and we are even worse. A good night and we kind of recover. Another good night and we are feeling better....and it goes on and on. Not as a binary yes/no, but as an analog rise and fall of differing amounts. So my caresheets are a reflection of what we are seeing works in captivity and not simply derived from weather data (though that plays a big part on analysis, of course).
So, what do we do when we have to put a number down on a caresheet and do not have the room for paragraphs of information to explain the gray area? We come up with a number or range that covers what we have seen be successful in captive conditions. So, bottomline, I don't have an answer for why they are so successful colonizing other areas when they are sensitive in captivity. I can only answer for why I place a priority on nighttime drops for Jackson's in my care summaries. The stresses of temperatures and humidities outside the ideal are cumulative and rise and fall as conditions dip in and out of the ideal range. So we are tasked with figuring out what that ideal range is and target that because our chameleons have a much less ability to adapt to the conditions they can tolerate when they are given no choices outside their limited cage space.
