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Really? Very interesting! Okay, last set of off-topic questions, I promise! How long does this semi-hibernative state last? Do you induce it by lowering the heat at the appropriate time, or do you watch for signs that he's ready for his hibernation and then lower the temp? And same questions for when it's time for him to come out of that state. Induced? Watching for signs?
I'd never heard of the tail fat thing, before. Loving this!
And last question, do reptiles indicate any kind of recognition of you? Or any preference for particular people?
I don't mind questions
Knowledge is meant to be shared! It was fortunate that Leo had to go to a vet very soon after getting him due to bad care information. The vet not knowing how to treat him and not wanting to let a little kids first pet die, hunted down a herpetologist at a zoo who was very kind in providing a treatment plan and all kinds of helpful info on how to take proper care of him (which was, unsurprisingly, very different than what the Petsmart "care sheet" he came with said). It's not widely known they enter a semi-hibernative state in the winter, so I was lucky to have learned that early on from a expert as I suspect it is one reason he's lived so long. He has not been kept constantly active or over-fed year round.
Keeping in mind I have never lived in a home with AC before (so very hot in the summer compared to winter) and do not use an under tank heater for him (he has a sunlamp that gets hot instead, on and off with the natural daylight cycle just like in nature), his dormant period is triggered by lower temps and decreased daylight. It is a very natural cycle and I don't really have to do anything 'special' to trigger it. It's not like he's sleeping for months on end like a hibernating bear either, but he is far less active and only eats about every 10 days-2 weeks. This period lasts about 3-4 months, with a gradual decline/rise in activity levels as days get shorter/longer and cooler/warmer.
Several species of geckos tails are designed to store fat for winter when it is cooler and food is less plentiful. It is natural for them to use up these fat stores every year and their tails get quite thin. When he was a younger gecko and eating tons of grasshoppers and leaf bugs and wild house crickets all summer long, his tail would get HUGE
. It always looked quite cumbersome to lug that thing around lol
Your last question is a difficult one. I wouldn't say reptiles form any kind of emotional bond with humans or even other reptiles, but can learn to recognize us. I do not know of any reptile species who lives in a social group in nature, raises it's own young or has a single mate for life. They may live in close proximity to others of their own kind peacefully, but don't think they have social structures of any kind thus do not posses the ability to form social bonds of any kind. They can be hand tamed and recognize humans handling them as a non-threat and many even enjoy humans because we are warm and reptiles seek heat being cold blooded. So, when Leo eagerly crawls up in a hand to curl up and hang out, he isn't doing it so much because he likes you or feels you are part of his social group, rather he recognizes humans as a safe source of heat and part of his environment. Likewise when Tiffany my bearded dragon would get 'excited' when I got home and wanted to come out and curl up around the back of my neck, she probably recognized me in the sense my neck was part of her "territory", just like her favorite hiding spot or basking spot. Or even Mr. Newt, who cannot be handled, comes out of his hiding spot when you come near his tank because he knows that a humans presence means food could be on it's way. Unlike a social animal like Kiwi who gets excited when he sees me or gets up on my hand or shoulder because he views me as part of his social group and wants to interact with me along with being conditioned that humans are safe and provide food or a place to hang out on. If any of that makes sense
! 
I don't know that he is long for this earth and I'm going to be devastated when he goes. He's just been with me so long and is such a gentle creature. Here's some pictures of my guy in his better days
