There isn't the exteme size difference in this Herring and the Lesser BB. Notice the much more uniform appearance of this Herring, and longer bill. Also notice, that this Herring shows no sign of a darker bar on the greater coverts, like the Lesser BB does. Some Herring's can show a darker area here though. As the winter progresses, the head on Herring's tends to pale, but the rest of the underparts usually keep the dark brown coloration shown here.

It is always easiest to seperate these two in the air, or with a flap. The Lesser BB lacks the window in the inner primaries always shown by Herring's, and has a double dark bar on the trailing edge of the inner wing from above, formed by the secondaries and greater coverts, Herring lacks this (though California is similar to Lesser BB in this regard), and Lesser BB shows much more contrast in the lightly-marked pale uppertail coverts and darker back, whereas this area blends together on American Herring's due to the heavier barring on the uppertail. The tail on Herring is dark, while on Lesser BB there is a broad dark band, but the base of the tail is white.