Sharp-beaked Ground-Finch Geospiza difficilis Scientific name definitions

Sharp-beaked Ground-Finch is an unusual and enigmatic species of Darwin’s Finch, and yes, it really does have a relatively long and pointed beak. This species currently occurs on three islands scattered through the Galapagos: Pinta in the north, Fernandina in the west, and Santiago in the west central part of the archipelago; it formerly occurred as well on Santa Cruz, but its presence there has not been confirmed since the late 1930s. Formerly this species also included populations found on Darwin and Wolf Islands and on Genovesa Island, but both of these now are considered to be different species (Vampire Ground-Finch Geospiza septentrionalis and Genovesa Ground-Finch Geospiza acutirostris, respectively). In contrast to Vampire and Genovesa ground-finches, which occur in arid scrub, Sharp-beaked Ground-Finch occupies dense forest in the highlands of the islands on which it occurs; otherwise its biology is relatively poorly known.

11–12 cm; 12·3–20 g. A small ground-finch with small, sharply pointed bill distinctly longer than it is deep and with culmen straight, giving more pointed and longer look than bill of G. fuliginosa; relatively short and weak-looking tail. Male is almost entirely black, with slightly browner wings and tail, undertail coverts with white fringes; irides dark; bill black during breeding period, becoming brown with orange tint at base and yellow at tip ­during transition, and orange-yellow during non-breeding; legs blackish. Female has head down to throat and upperparts dark olivaceous-brown with brownish or olive-grey fringing (head looks weakly streaked and upperparts rather scaly); wing dark brown with buff fringing, tail feathers dark with greyish edging; buff upper half of eye ring; underparts boldly streaked dark brown and buff, the streaks becoming obscure on rear underparts, undertail coverts rather plain whitish-buff; bill dark with orange tint at base and yellow tip, ranging to entirely orange-yellow (depending on breeding state), legs blackish. Immature male is intermediate between streaked female and solidly black adult male, has head usually solidly black, as is breast, but diffuse streaking present on belly and back, wings more blackish than on female, and wing coverts and tertials crisply edged buff. Form “debilirostris” is large, with proportionately large feet, and proportionately thick-based, sharply pointed bill.

Pinta, in N Galapagos Is, and Fernandina and Santiago, in W & C Galapagos Is. Previously recorded on Santa Cruz (last seen between 1932 and 1939), Floreana and San Cristóbal (3 Wiedenfeld, D.A. (2006). Aves, The Galapagos Islands, Ecuador. Check List 2(2): 1–27. Close ).

In highlands of Fernandina, Santiago and Pinta occupies structurally complex and dense Zanthoxylum forest.

Resident; highland populations appear to drift lower into drier habitats during non-breeding season.

Variety of foods, including leaves, flowers, cactus pulp and insects. All feed nestlings on mixed diet of arthropods, fruits and seeds. Seeds of Bursera graveolens absent from diet of small-billed present species, but common in that of large-billed G. magnirostris. During non-breeding season diets diverge, and seed size eaten then correlates to bill size.

Males of genus, with rare exceptions, sing only one song type. Song of present species exhibits much geographical variation: in forest-based populations of Fernandina, Santiago and Pinta songs complex both in tempo and in note structure, and have much frequency modulation and use of high-pitched notes. Calls include very high “tzeeeewwww”.

Highland populations breed largely during wet season. Nest built by male, a sphere with entrance towards top and on side, made from dry grasses and vegetation. Clutch usually 4 eggs, whitish with pinkish or brown spots; incubation period 12 days (10–14); nestling period 13–15 days (11–17).

Not globally threatened (Least Concern). Common on N arid low islands, uncommon in highlands. Widespread, and generally showing no signs of any decrease in numbers, although possibly extirpated on Santa Cruz.

Alvaro began birding as an 11 year old in Canada, and eventually trained in Evolutionary Ecology studying, creatures as varied as leaf-cutter ants and Argentine cowbirds. But his career has been focused on birding tourism, both as a guide and owner of his tour company, as well as a avitourism consultant to various organizations. He is the author of Birds of Chile, New World Blackbirds: The Icterids, as well as the ABA Field Guide to the birds of California. He lives in Half Moon Bay, California where he is known for his pelagic birding trips. Email: alvaro@alvarosadventures.com.