Genovesa Cactus-Finch Geospiza propinqua Scientific name definitions

Genovesa Cactus-Finch formerly was considered to be conspecific with the Española Ground-Finch (Geospiza conirostris), as a polytypic Large Cactus-Finch (Geospiza conirostris). Genetic analysis indicates, however, that Genovesa Cactus-Finch is more closely related to Common Cactus-Finch (Geospiza scandens) than it is to Española Ground-Finch. These genetic results are not surprising, at least in hindsight, as other researchers earlier had documented that Genovesa Cactus-Finch and Española Ground-Finch also have different songs. Genovesa Cactus-Finch is common and widespread on Genovesa, in the northeastern corner of the Galápagos Archipelago. Another taxon, darwini, is reported from Darwin and Wolf Islands, in the northwestern Galápagos, but the status of this population is unresolved: some authorities classify darwini as a subspecies Genovesa Cactus-Finch, but is here treated as a subspecies of Large Ground-Finch (Geospiza magnirostris), whereas others question whether it is a valid subspecies at all.

13–15 cm; 28 g. A large cactus-finch (slightly smaller than formerly conspecific Española Ground-Finch (Geospiza conirostris)) with thick, yet long and robust bill; relatively short and weak-looking tail. Male is entirely black with slightly browner wings and tail, except white vent with black feather centers on undertail coverts; iris 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 is brownish gray and streaked throughout, with the paler feather fringes on head, back and most of breast often narrow and indistinct, giving the bird a fairly solidly dark appearance; often with paler buffy-gray supercilium and paler lower eye-crescent (on darker birds, supercilium restricted to a pale spot above and behind eye); upperwing brown with paler, buffy-brown wingbars and tertial edges; below, off-white with darker brown streaking, most dense on throat and breast (breast and throat on some solidly brownish), least dense on belly and vent, undertail coverts with broad whitish fringes; bill dusky with variable amounts of dull orange, especially on mandible, varying to entirely orange-yellow (depending on breeding state). Immature male is inter­mediate between streaked female and solidly black adult male, 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.

Distinguished from very similar Large Ground-Finch (Geospiza magnirostris) by longer and thinner bill, which is more laterally compressed than that of almost identical Española Ground-Finch (Geospiza conirostris) (1 Ridgway, R. (1894). Descriptions of twenty-two new species from the Galapagos Islands. Proc. US Natl. Mus. 17(1007): 357–370. Close , 2 Ridgway, R. (1897). Birds of the Galapagos Archipelago. Proc. US Natl. Mus.. 19: 459–670. Close ). In females, the the paler feather fringes on the head, back and most of the breast are narrow and indistinct, giving birds a more solidly dark appearance compared to females of congeners.

Geospiza propinqua Ridgway, 1894, Proceedings of the United States National Museum 3:361. Type locality given as "Tower Island, Galapagos" [=Genovesa Island, Galapagos] (1 Ridgway, R. (1894). Descriptions of twenty-two new species from the Galapagos Islands. Proc. US Natl. Mus. 17(1007): 357–370. Close ).

Previously considered conspecific with Española Ground-Finch (Geospiza conirostris). Hybridizes rarely with Large Ground-Finch (Geospiza magnirostris), and also with smaller Genovesa Ground-Finch (Geospiza acutirostris). The taxon darwini, commonly placed in "Geospiza conirostris" (often also including present species; 3 Dickinson, E. C., and L. Christidis, Editors (2014). The Howard and Moore Complete Checklist of the Birds of the World. Fourth Edition. Volume 2. Aves Press, Eastbourne, UK. Close ), has not been sampled in recent molecular analyses, but on geographical grounds and given its slightly larger bill than Genovesa Cactus-Finch, it is here assigned to Large Ground-Finch (e.g., 4 Grant, P.R. (1986). Ecology and Evolution of Darwin’s Finches. Princeton University Press, Princeton, New Jersey. Close ). Based on available data, darwini appears to be extremely variable, showing a slight bimodal distribution in bill size and shape, with some closer to Large Ground-Finch, and others closer to Genovesa Cactus-Finch, suggesting that this variability may be the result of hybridization, where Large Ground-Finch is one of the parents (4 Grant, P.R. (1986). Ecology and Evolution of Darwin’s Finches. Princeton University Press, Princeton, New Jersey. Close , 5 Gill, F., D. Donsker, and P. Rasmussen, Editors (2023). IOC World Bird List (v13.1). Close ). However, Grant (4 Grant, P.R. (1986). Ecology and Evolution of Darwin’s Finches. Princeton University Press, Princeton, New Jersey. Close ) noted that all specimens were most similar to Large Ground-Finch in terms of the curvature of the sides of the bill, resulting in their tentative placement with Large Ground-Finch.

In a series of molecular phylogenetic studies, including analyses with whole genome-resequencing, Genovesa Cactus-Finch was found to be sister to Common Cactus-Finch (Geospiza scandens) (6 Lamichhaney, S., Berglund, J., Almén, M.S., Maqbool, K., Grabherr, M., Martinez-Barrio, A., Promerová, M., Rubin, C.-J., Wang, C., Zamani, N., Grant, B.R., Grant, P.R., Webster, M.T. and Andersson, L. (2015). Evolution of Darwin’s finches and their beaks revealed by genome sequencing. Nature. doi:10.1038/nature14181. Published online 11 February 2015. Close , 7 Rubin, C.-H., E. D. Enbody, M. P Dobreva, A. Abzhanov, B. W. Davis, S. Lamichhaney, M. Pettersson, A. T. Sendell-Price, C. G. Sprehn, C. A. Valle, K. Vasco, O. Wallerman, B. R. Grant, P. R. Grant, and L. Andersson (2022). Rapid adaptive radiation of Darwin's finches depends on ancestral modules. Science Advances 8:eabm5982 Close ). Outside of this close sister relationship, its relationship with other members of the Darwin's finch radiation is less clear, although Genovesa Cactus-Finch and Common Cactus-Finch together may be sister to Large Ground-Finch (Geospiza magnirostris) and Española Ground-Finch (Geospiza conirostris) (6 Lamichhaney, S., Berglund, J., Almén, M.S., Maqbool, K., Grabherr, M., Martinez-Barrio, A., Promerová, M., Rubin, C.-J., Wang, C., Zamani, N., Grant, B.R., Grant, P.R., Webster, M.T. and Andersson, L. (2015). Evolution of Darwin’s finches and their beaks revealed by genome sequencing. Nature. doi:10.1038/nature14181. Published online 11 February 2015. Close ), or it may be sister to a larger radiation of Geospiza that also includes Small Ground-Finch (Geospiza fuliginosa), Genovesa Ground-Finch (Geospiza acutirostris), and Medium Ground-Finch (Geospiza fortis) (7 Rubin, C.-H., E. D. Enbody, M. P Dobreva, A. Abzhanov, B. W. Davis, S. Lamichhaney, M. Pettersson, A. T. Sendell-Price, C. G. Sprehn, C. A. Valle, K. Vasco, O. Wallerman, B. R. Grant, P. R. Grant, and L. Andersson (2022). Rapid adaptive radiation of Darwin's finches depends on ancestral modules. Science Advances 8:eabm5982 Close ).

Darwin's finches are well-known to hybridize with each other, and Genovesa Cactus-Finch is no exception. It has been documented hybridizing with both Large Ground-Finch and Genovesa Ground-Finch (8 Grant, B.R. and Grant, P.R. (1989). Evolutionary Dynamics of a Natural Population. The Large Cactus Finch of the Galápagos. University of Chicago Press, Chicago & London. Close , 9 Grant, P. R., and B. R. Grant (1996). Speciation and hybridization in island birds. Philosophical Transactions: Biological Sciences 351(1341):765-772 Close ). In one study, mixed pairs between a Genovesa Cactus-Finch and another species represented about 1% of all pairs observed (n = 333 pairs), including one between a male Genovesa Cactus-Finch and female Genovesa Ground-Finch which did not successfully produce young, a pairing of a female Genovesa Cactus-Finch and a male Large Ground-Finch which did successfully produce young, and a pairing between a male Genovesa Cactus-Finch and a female Large Ground-Finch which also successfully produced young (8 Grant, B.R. and Grant, P.R. (1989). Evolutionary Dynamics of a Natural Population. The Large Cactus Finch of the Galápagos. University of Chicago Press, Chicago & London. Close ). In addition to the mixed pairs, probable hybrids were also documented that were likely the offspring of pairings between Genovesa Cactus-Finch and both Large Ground-Finch and Genovesa Ground-Finch. Hybrids and hybrid pairs did not appear to show any differences in the number of young fledged, but presumed hybrids did not seem to survive as long as the parental species (8 Grant, B.R. and Grant, P.R. (1989). Evolutionary Dynamics of a Natural Population. The Large Cactus Finch of the Galápagos. University of Chicago Press, Chicago & London. Close ).

Found on Genovesa, in the northeastern Galapagos Islands.

Arid lowland areas of dry scrub, as well as areas with prickly pear cactus (Opuntia).

Presumably sedentary.

Feeds on prickly-pear (Opuntia) cactus pulp, flowers, fruits and insects. In one study, adults of present species, Genovesa Ground-Finch (Geospiza acutirostris) and Large Ground-Finch (Geospiza magnirostris) showed much overlap in food during nesting period, all provisioning nestlings with mixed diet of arthropods, fruits and seeds. Seeds of Bursera graveolens absent from diet of small-billed Genovesa Ground-Finch, but common in that of large-billed Large Ground-Finch, while parts of Opuntia helleri were fed to young of Genovesa Cactus-Finch. During non-breeding season diets diverge, seed size eaten then correlating with bill size.

Song a fast doubled rolling series of burry musical churring notes, “cheeurrr-r-r-r-r-r cheeurrr-r-r-r-r-r” or series of similar notes repeated more slowly and deliberately 3–10 times, “cheuu cheuu cheuu cheuu cheuu cheuu cheuu” . Calls include a high-pitched “tzeeeeeer” as well as elements with similar quality to song.

Season January–May, beginning within a week of first rains; up to four clutches within one season. Nest built by male, a sphere with entrance towards top and at side, made from dry grasses and other vegetation. Clutch usually four eggs, whitish with pinkish or brown spots; incubation period usually 12 days (range 10–14); nestling period typically 13–15 days (11–17).

VULNERABLE. Restricted-range species: present in Galápagos Islands Endemic Bird Area. Common within its tiny range (Extent of Occurrence is 19 km²; Birdlife International 2019). Global population estimated at fewer than 1,000 mature individuals (Birdlife International 2019). Appears not to be undergoing any detectable population decline, but is vulnerable to stochastic events. The invasive parasitic fly, Philornis downsi, which causes high nestling mortality in landbirds elsewhere in the Galápagos Archipelago (10 Kleindorfer, S., Peters, K.J., Custance, G., Dudaniec, R.Y. and O’Connor, J.A. (2014). Changes in Philornis infestation behavior threaten Darwin’s finch survival. Current Zool. 60(4): 542–550. Close ), has not reached Genovesa (11 Fessl, B., Anchundia, D., Carrión, J., Cimadom, A., Cotin, J., Cunninghame, F., Dvorak, M., Mosquera, D., Nemeth, E., Sevilla, C. and Tebbich, S. (2017). Galapagos landbirds (passerines, cuckoos, and doves): status, threats, and knowledge gaps. Galapagos Report 2015–2016: 149–160. Close ).

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.