Thrush...

Any birder who identifies birds following the dictates set out in the field guides--shape, bill length, habitat, range--will immediately, naked eye, identify this one as an American Robin.  Fortunately, this is what I did this morning at Colony Farms, just east of Vancouver. 
However, when I took a closer look,  I have to admit I got to thinking.  Not questioning my identification, but rather marveling at how much pattern and color invite confusion into birding!  Without a doubt the bird has what I think of as a thrush-like posture: rather erect and 'tall'.  Its bill is appropriately-sized: neither too long for its head like Long-billed Curlew nor too short, like Bushtit!  The bird is where it's supposed to be--on a grassy lawn--and as American Robins are common throughout the area, its appearance is nothing out of the ordinary. 
But had I relied on the coloring of the bird I might have been thrown; based on that (and actually supported by the habitat), Fieldfare jumped to mind.  Also a thrush, Turdus pilaris is the same length.  Both birds also have a nice white supercilium.  Furthermore, like the bird pictured above, the Fieldfare is not uniformly colored on the breast--though it has streaks (i.e., the 'arrows' of the 'pilaris') rather than blotches.  The two thrushes have a similar stance. 

The telling difference, of course, is that I have just described an adult Fieldfare and the above American Robin is a recently-fledged one: he's still going to attain his uniform color.  Also, there's the helpful aid of range maps: Fieldfares do not occur with any regularity in the New World:  as the Nat Geo Complete Birds of North America notes they are a 'casual vagrant in northeastern North America'; 'accidental to Ontario and Minnesota'; and 'casual in western Alaska'.  Still, there's always a first time...