Medium Ground Finch
Geospiza fortis
Like the other members of its genus, the medium ground finch is strongly sexually dimorphic; the female's plumage is brown and streaky, while the male's is solid black, with white tips to the undertail coverts. The bird measures 12.5 cm (4.9 in) in length—which falls between the lengths of the small and large ground finches. The bill of this species is quite variable in size, though the length of the upper mandible is always greater than the depth of the bill at its base. The wing shape, on average, seems to change with ecological shifts.
ID text from Wikipedia, CC BY-SA 4.0
Small Ground Finch
Geospiza fuliginosa
The small ground finch is the smallest of the ground finches, measuring 11 cm (4.3 in) in length. Its beak is short and pointed, with a slightly curved culmen. On average, its beak is smaller than that of the medium ground finch, but there is a significant overlap in size between the two, particularly on islands where only one of the two species exists. On islands where the two species compete directly, the difference between their beaks are greater. The male is black with white-tipped undertail coverts, while the female and young are brown with streaked underparts. Voice: The small ground finch's song is rapid and weak and is transcribed as "twichooo-twichooo" or "teur-weee".
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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Play today's Daily BirdPhotos and recordings are credited to their authors under the licence shown. Full profiles: Medium Ground Finch and Small Ground Finch.