This is my favorite link, at least for birds in my area. It shows me just how similar some can be, especially the females.
http://www.sialis.org/otherbrownbirds.htmIt can be tricky at first until you get accustomed to the changes in plumage throughout the year. My rule of thumb is that no matter how much it looks like an English sparrow, if it has a speckled breast, it's a "friendly", don't shoot.
Make sure you glass those birds before you shoot.
Good luck.
M
P.S. The white throated sparrow for some reason looks a whole lot like a house sparrow. If you see yellow between the eye and beak, it's a friendly.