Percentages are rounded to nearest 5 for individual localities. Cantabrican, W Portugal/NW Spain cline, Dark form and Mediterranean intersection are defined in the text.

+ -- noted but less than 3%.

Key: S Sample size;

Mantle colour: RB Ruddy Brown as in some worn michahellis; RT Ruddy Tinge to grey-brown as in michahellis or argenteus; GB Grey-Brown as in graellsii;

Mantle texture: SC Scaley as in marinus; LC Less contrasting as in graellsii/argenteus;

Bill colour: BL all-black as in graellsii; PB black with pale base as in argenteus; birds categorised as PB if base is pale to any extent.

Tertials: PF narrow pale fringe around grey-brown centre as in graellsii; PT large pale tip and narrow pale fringe to dark grey-brown or rusty-brown centre; PC large pale tip and fringe with pale internal markings as in some argenteus; PN narrow pale fringe with slight notching on each sides of feather.

Percentages are rounded to nearest 5 for individual localities. Cantabrican, W Portugal/NW Spain cline, Dark form and Mediterranean intersection are defined in the text.

Key: S Sample size;

Underwing pattern: UN Uniform as in graellsii; CS some contrast between coverts and outer wing as in michahellis or marinus; CM marked contrast;

Tail colour: BR Bright as in graellsii; DL Dull as in argenteus; birds categorised as BR if tail gleams significantly and only a small number of dark flecks cover the pale area.

Inner wing: 2B two bars present as in graellsii; 1B one bar present as in argenteus; birds categorised as 2B if the greater coverts bar is obvious in flight.

Pale primary panel: OB Obvious as in argenteus; IN indistinct as in michahellis; NO None as in graellsii; birds categorised, seen from below, as OB if pale primary panel is a striking feature and as IN if the pale area is present but needs to be searched for; from above, where this feature is less easy to view, OB would indicate a clear pale area and IN a palish area compared to the surrounding area; in both cases NO indicates no trace of a pale area.

Percentages are rounded to nearest 5 for individual localities. Cantabrican, W Portugal/NW Spain cline, Dark form and Mediterranean intersection are defined in the text.

Key: S Sample size;

Head markings: Dusky as in argenteus; White, except for dark eye spot, as in Mediterranean michahellis; birds categorised as DS, if as well as the dusky eye spot, there is at least an extensive dusky wash over the back of the head, the sides of the head and the loral area.

Breast and Belly Streakings: Heavy as in graellsii; Sparse as in Mediterranean michahellis; White as in bleached Mediterranean michahellis.