we don't live in the Antarctic(sp??)most of the birds stay over winter,like Cardinals,Bluejays,Sparrows,Starlings etc..they just find themself a nice "sucker"like me and hubs,who feeds them all winter and give them a heated bird-bath.
Also we have thick Cedar-Hedges where they can get shelter.
As for the Sparrow,yes he can get through the hole,he's aalready furnished his house,my other bird-houses have small holes to,that way they can be a little safer.
The squirrels are funny,real little Monkeys..
Also,with all the rain we've had,everything is popping out of the ground,The Magnolia ready to bloom,as is the Lilac-tree,the grass is growing like crazy,I LOVE this time of year.