two black-headed gulls are almost indistinguishable from each other

affinity associations beak bill bird birding birds blackheaded breeding commonality conformity congeniality didymi didymus different each feathers fowl guide gull gulls indistinguishable kinship larus legg legged legs likeness mew monopode one onefooted onelegged other pair peas plumage quite resemblance ridibundus sameness seagull semblance sibling similarity similitude slenderbilled tour twin twins two unijambist uniped watching water white wild