Grey Tree Frog

Question
Hi, I recently discovered a Grey Tree Frog that had hitched a ride inside a plant I brought in for winter. My question is, I would like to put him back outside. I live in Michigan and it is already very cold here. Can he go from the warm house to the cold outside in order to hibernate? If so, does this need to be done gradually? I love these guys but I am a firm believer in letting wild beings keep to their natural order. I am prepared to keep him in until spring if necessary.
Thank you, Fran

Answer
Hi Fran,

I am also a fan of the greys and would agree that returning him to the wild is in his best interest. How to do it safely is indeed the catch!
Greys are one of the numerous types of frogs that can endure cold temperatures through the production of a anti-freeze/glycerol type substance in their cells. I honestly don't know how quickly this production can take place and how much acclimation or exposure they need to the colder temperatures to trigger it.

I think your weather is quite similar to ours (southern Ontario) at this stage with near freezing temperatures in the morning and evening but still with some sunny more moderate daytime temps.
I would suggest releasing him during the warmest part of one the  next few days ideally in a wooded area with some loose soil, leaf debris and logs.
They can also be hibernated artificially by creating an aerated box with a combination of peat moss, plain potting soil and vermiculite that he can burrow into. An enclosed porch or garage would be a suitable spot for that.
Lastly, you can house him over winter in a terrarium with a similar substrate and some plants and bark for hiding in. Offer him a small dish of dechorinated water and some small feeder crickets.
You may find that he still enters a semi-dormant stage and remains buried even at normal room temperature during this time.