Pacific Golden-Plover

Cf. American Golden-Plover.  Pacific and American Golden-Plovers were long regarded as a single species, known collectively as the Lesser Golden-Plover.  They are very similar and overlap in most visible characteristics, so many individuals are ambiguous and require a close study to distinguish—and in some cases even a close study is inconclusive.

Adults in fully or nearly fully breeding plumage can usually be identified based on the distribution of black and white on the underparts.  American has wider white patches on the sides of the chest and more extensive black on the belly, extending back to the undertail coverts and showing little if any white on the sides and flanks.  Conversely, Pacific has narrower white patches on the sides of the chest, wider white borders on the sides and flanks, and all or mostly white undertail coverts.

In other plumages, Pacific typically appears warmer, yellower, more “golden” overall, whereas American typically appears colder, whiter, and grayer.  The difference in shading tends to be most pronounced on the face, neck, and belly.  However, both species vary considerably.  Some Pacifics appear far whiter or grayer than average, and some Americans appear for yellower.  The tendencies are not consistent enough to be a reliable distinction.

The most consistent difference appears to be wing length, detected as the projection of the primary tips (which are uniform dark-gray) beyond the tertials (which have a noticeable pattern of pale spots).  On most Americans, the primaries project about an inch or more past the tertials.  On most Pacifics, the primary tips are barely visible.  This distinction seems to be fundamental enough to be reliable when observed.  Nevertheless, there are certain molt conditions in which each species can briefly masquerade as the other: i.e., when a Pacific’s tertials are worn, or an American’s primaries are growing in.

Other distinctions that may be helpful in some cases include facial pattern and overall structure or posture (incorporating leg and tail length).  Facially, American usually shows more contrast between its pale, whitish eyebrow and dark crown, and a less pronounced ear-spot.  Pacific tends to show a yellower eyebrow and larger, darker, more pronounced ear-spot.  Structurally, American has a slightly longer tail and shorter legs, so its overall appearance is lower and longer, whereas Pacific has a proportionately shorter tail, longer legs, and slimmer, more vertical posture.