|BERRIEN COUNTY, MICHIGAN. 09 OCTOBER 2015.|
Let's start with the standing black-backed. It clearly outsizes the other two individuals that are at rest. Not only because it's standing, but because it's genuinely large-bodied, big-headed and large-billed. This is the largest gull species on the planet: Great Black-backed Gull. The extensive black-marked bill and brown greater coverts and tertials suggest a 3rd cycle type, not an adult.
The other black-backed with mostly black bill, white head and pale iris is its smaller cousin - Lesser Black-backed Gull (2nd cycle type). The light gray adult-type to the far right appears to be a Herring Gull, although one would want better views to be certain.