Tiger Salamander behavioral changes

We've had our Tiger for a little over a year, for the last few months I have noticed several behavioral changes that have recently become marked. Spot (kids named him) started off at about 4 inches in length, in the last year he's grown to about 9 inches. We started off feeding him captured earthworms, but moved to Canadian night crawlers about 6 months ago because he's grown so much he'd eat two or three good sized earthworms three times a week. He's always been very active and and aggressive, attacking anything that went past his face on a regular basis, including my fingers. After the first month or so, he's never minded being handled, If he saw someone outside the tank he would move toward them, I think anticipating being fed. In any case, over the last three months or so he's become reticent about being handled, actively attempting to escape from your hands. About three weeks ago I moved him to a much larger enclosure, I also moved from a river gravel and garden soil substrate to straight coco husk.
Now, he burrows immediately and stays buried most of the time. However I do see evidence that he's coming out at night and moving around the tank. Of more concern is he has shown little interest in food for the past two weeks, normally, if he was aware of a person near the tank he would actively move toward them and climb the tank wall if he was hungry. Now he stays buried in the coco husk all the time during the day. Also, he's not climbing into his water bowl to defecate. I am concerned.
He's in a 20 gallon Critter Cage with about 3 inches of coco husk in the bottom, he has some rocks and pine cones to climb on and hide under. He has a shallow six inch round water bowl, we replace his water with distilled water every couple of days or when fouled.
His enclosure is indoors, situated near windows so he gets some natural sunlight.
My questions:
Do Salamanders kept in indoor enclosures hibernate during the winter? He didn't last winter.
Will ingesting the coco husk (it gets stuck to the worms) hurt him in any way.
Does he need any dietary supplements?
Thanks for your help.
MDH

Have you had a good look at him recently, do you think his body condition has deteriorated?
I noticed mine quietened down a bit when the temperatures dropped.

No, I dug him out last night and he looks fine and he's active, he just seems more interested in burrowing than eating.
Thanks

My experience with tigers that I have gotten from folks that kept them on gravel or other substrate that doesn't allow burrowing is that they will bury themselves for long periods of time ( like for several weeks) as soon as they have the chance. I have had 5 tigers that have exhibited this prolonged self burying behavior. As long as body condition seems fine I think your salamander will be just fine.
I would recommend discontinuing use of distilled water and change to aged tap water or something else that has minerals in it - distilled water can cause cellular imbalance as it has little or no ions in it. I know your tiger does not live in its water bowl but even a short amount of time in distilled water seems less than ideal to me.
Heather

Thanks Heather

I would get rid of the pine cones. Pine and cedar woods have oils that are toxic to salamanders. I would also provide a cave-type of hide - tigers will often use this in lieu of burrowing and you may see it/its head more often. Tigers do not hibernate, they will brumate but not if kept at moderate temps.

For answers to your other questions and further information, please see this article:

Caudata Culture Articles - Tiger Salamander 101