Hi Roy.. Lovely frog tank..
They travel allright..
i find them in my garden pond all the time.. I live on top of a hill smack dab in the middle of some waters and still some choose my little pond to play around in. If i take the distances between the waters they have to travel 1 or 2 miles.
I used to have a small ditch under the bathroom window in the garden. Don't know how it's called in english. Dig a hole, place bricks around, tadaa plantpot. Something like that..It is like 90x30x40cm Anyway did put pond foil in it, water and swamp plants. every spring i did clean it and also took the foil out and regularly found frogs and even salamanders under the foil hybebernating.
No idea why they would travel about a mile up hill to hybernate at my place.
No idea if the could survive hybernation on a balkoni. tho in my garden they did 40cm deep under the pond foil filled with water.. i guess that also freezes rock solid when cold enough. Anyway they dig in to hybernate, so you would need to give 'm something like that. Dirt and old leaves.. Something with straw insulation might do, what many people use to make sensitive plants survive the freezing winters.