Hmmm.... I suppose you'd have to know what kind of materials it was made out of to make sure they were all bird safe (including the hoop underneath everything else). It could be fun to make an xmas wreath for the birds though! I'll have to look into that.
"I bet the sparrow looks at the parrot and thinks, yes, you can talk, but LISTEN TO YOURSELF!" ~ Jack Handy ~ Deep Thoughts
I don't know. Most sources suggest heating fresh wood and pine cones to sterilize them. And the goo from a fresh tree could get messy. But... it is a tree... how bad could it be? As long as its a wood that's listed as not particularly toxic. It would be pretty fun to make a bird tree decorated with toys and stuff!
I think it would be kind of cute to take Christmas pictures of Einstein and the budgies on the Christmas tree. Now if they only had little Santa hats...
The christmas trees sold here in Sweden are often treated with something to stay fresh for a longer time, but I´m not completely sure. If it´s an untreated, common spruce or pine tree it should be okay, but there are a lot of different species out there and some of them are toxic.