You may find this link useful George (if you haven't already come across it) -
http://www.wild-bird-watching.com/junco.html.
This describes the
Dark-eyed Junco which is commonly referred to as the 'snowbird.' The confusion, and hence the inconsistency of the description, that surrounds the term
snowbird is the reference to birds arriving in areas where snow appears - not a very technical or helpful term really
Anyway, it's not a UK visitor so we're not likely to see it over here.
Robins are all year round UK residents, so you've probably been a bit unlucky not to have seen much of them in your garden George. They are very territorial, and most Robins in Britain and Ireland don't move more than 5km. So once they arrive in your garden they are there to stay
We have a resident Robin, and Blackbird, in our garden which we see several times daily. The song of the Robin is absolutely gorgeous, so melodic, and is one of my favourite songbirds.
As regards to the thrushes George, that is a more alarming situation. The
Song Thrush is experiencing a moderate decline in population - by over 50% between 1969 and 2006, with a slight recovery in recent years. The
Mistle Thrush to a slightly lesser degree. Population fall by 45% since 1969 but this decline is believed to have now ceased.
In the New Forest where we live, the food sources and breeding potential is much more favourable to all specieis of birds. I still put out seed and nuts in our garden feeders all year round. Once you start to do this you should continue throughout the year as they rely on this as a stand-by food source. It is particularly important when the frosts arrive making ground-foraging difficult for them.
And a contant fresh water source should not be forgotten. We keep our bird-bath topped up with clean and ice-free water as much as possible.