LOL. Good effort. Even with clean glass though, I find I lose a stop in exposure speed shooting though glass and get a very curious colour cast on images due a tint in the double glazing which isn't at all obvious looking at the glass.
You need to open the window if you can, and put up with the missus moaning about all the heat going out of the house.
Really though while we all do it, it's lazy bird photography, and if you go outside those birds will get used to you much sooner than you think. You don't necessarily need to be concealed, just keep pretty still - it's sudden movements which spook them. You'll be able to get closer but a few simple rules helps a lot.
Wrap up warm with proper gear and it's not as cold as you might think.
Keep low which is less intimidating to the birds, so getting seated behind a tripod achieves that and it's a lot more comfortable.
It's your hands and face which the birds will see the most. They appear almost luminous to birds, so wear a hat and gloves to keep that skin out of sight as much as possible. Some people wear a face veil for that reason.
Keep your hand and head movements slow and deliberate and you wont spook the birds. They're ravenously hungry in this cold weather and they'll soon get used to you sitting there and come to the feeders.