This bird has the potential to be confused with first-year Black-headed and Little Gulls but there are features consistent to eliminate both of those, apart from it was in Texas at Rollover Pass in April 2008.
Note the following:
- Slender all dark bill; longer than on Little Gull and not long or red enough for Black-headed Gull
- Small and isolated dark ear spot that really doesn't extend up and onto the crown.
- Whitish crown, Little Gull has a dark cap whilst on Black-headed there is a variable amount of extension from the ear spot and from above the eye (creating a diffuse double line)
- Grey wash to the hind-neck, neck sides and breast sides which is totally absent on both Little and Black-headed Gulls (also present on adult Boneparte's Gulls)
- Legs are a distinct pale pink colour; muddy orange-red on Black-headed Gull and dull pinkish on Little Gull.
Bird aged by the brown tertials and brown centred lesser coverts whilst the primaries broad white edges, would not show on Black-headed Gull.
Boneparte's Gull, 1st-winter Bodega Bay Harbour, November 2009.
This flight shots clearly demonstrates the upper-wing pattern. Note the black 'trailing' edge, the black lesser coverts, the whitish 'window on the inner-primaries, mid side black ear spots and the grey shawl.
The tail is white with very black narrow tail band. The bill is black and slender.
The underwing is whitish with the primaries also be very pale, almost translucent bordered by black. On Black-headed Gull the primaries are dusky.