Thick-billed siskin

Thick-billed siskin
Male
Female
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Fringillidae
Subfamily: Carduelinae
Genus: Spinus
Species:
S. crassirostris
Binomial name
Spinus crassirostris
(Landbeck, 1877)
Synonyms

Sporagra crassirostris
Carduelis crassirostris

The thick-billed siskin (Spinus crassirostris) is a species of bird in the family Fringillidae, the finches and euphonias.[2] It is found in Argentina, Bolivia, Chile, and Peru.[3]

Taxonomy and systematics

The thick-billed siskin was originally described in 1877 with the binomial Chrysomitris crassirostris.[4] It was later moved to what was then the subgenus Spinus within genus Carduelis and also spent time in genus Sporagra. Beginning in about 2009 the subgenus was elevated to full genus level and the yellow-rumped siskin, the rest of the New World siskins, and the New World goldfinches were therefore elevated to now-genus Spinus.[5][6][7]

The thick-billed siskin has two subspecies, the nominate S. c. crassirostris (Landbeck, 1877) and S. c. amadoni (George, W. G., 1964).[2] Some birds with colors intermediate between those of the two subspecies are postulated to be a third subspecies.[8]

Description

The thick-billed siskin is one of the larger members of genus Spinus and has the eponymous thick bill. It is 12.5 to 14 cm (4.9 to 5.5 in) long and weighs about 19 g (0.67 oz). The species is sexually dimorphic. Adult males of the nominate subspecies have a black head, neck, and throat with a thin yellow band around its lower edge. Their back and scapulars are olive-yellow with indistinct darker streaks. Their rump is greenish yellow and their uppertail coverts somewhat yellower. Their tail is mostly black with wide yellow edges at the bases of all feathers but the innermost. Their wings' median and greater coverts are blackish brown with yellow or yellowish green tips. Their primary coverts and flight feathers are mostly black. Their primaries and secondaries have wide yellow bases and the ends of the secondaries have light buff edges. Their tertials have thin pale or whitish buff edges and tips. Their breast and flanks are bright yellow, often with a greenish tinge on the flanks. Their belly to undertail coverts are bright yellow or yellowish buff. Adult females have a dark gray head and nape and a grayish olive chin and throat. Their upperparts are mostly green or greenish olive with buff flecks and an olive-yellow wash on the rump. Their tail and wings are much like the male's but with less yellow. Their breast is dingy yellow and their belly to undertail coverts off-white. Juveniles are mostly buffish brown with pale yellow undertail coverts.[9]

Subspecies S. c. amadoni has a smaller bill than the nominate. Males have a duller black head and duller olive back. Their rump is olive and their uppertail coverts olive with grayish tips. Their tail has little or no yellow and their wings less yellow than the nominate. Their underparts are a much duller yellow than the nominate's with an olive tinge on the breast and whitish or pale yellow lower belly and vent. Females resemble the nominate but with their rump and uppertail coverts almost the same color as their back. Their underparts are grayish white with dusky streaks on the lower flanks and undertail coverts. Both sexes have a brown iris, a brown maxilla, a brownish horn mandible, and dark gray or blackish legs and feet.[9]

Distribution and habitat

The thick-billed siskin has a disjunct distribution. Subspecies S. c. amadoni is the more northerly of the two. It is found from Ancash Department in northwestern Peru south to extreme northern Chile and east into northwestern Bolivia. The possible third subspecies occurs in the northern half of that range.[9][8] The nominate subspecies is found in southern Bolivia, northwestern Argentina, and central Chile.[9] The species primarily inhabits Polylepis woodlands and shrublands and also brushy hillsides and areas with stunted trees. In elevation it ranges between 3,000 and 4,800 m (9,800 and 15,700 ft) overall and 3,600 and 4,600 m (11,800 and 15,100 ft) in Peru.[9][8]

Behavior

Movement

The thick-billed siskin's migratory behavior is not well known. It appears to be a partial migrant, with some individuals moving from higher elevations to lower ones and others from south to north after the breeding season. At all seasons but especially the non-breeding one it is somewhat nomadic.[9]

Feeding

In the breeding season the thick-billed siskin feeds almost entirely on the seeds, buds, and shoots of Polylepis. It apparently has a more varied diet in the non-breeding season, which may be spent away from the Polylepis zone. It forages in pairs and small flocks during the breeding season and in larger flocks after it; the latter may include other species of siskin. It forages acrobatically in trees and often hangs upside down on thin branches.[9]

Breeding

The thick-billed siskin's breeding season has not been defined but apparently includes November to March. Nothing else is known about the species' breeding biology.[9]

Vocalization

The thick-billed siskin's song is "a series of twitters" similar to that of other siskins but delivered faster and at a lower pitch.[9] Its calls include "a wheezy hew-li?, a mewing rhee?, and a low chatter".[8]

Status

The IUCN has assessed the thick-billed siskin as being of Least Concern. It has a large range; its population size is not known but is believed to be stable. No immediate threats have been identified.[1] It is considered overall "locally common to rare" and infrequently recorded.[9] It is considered rare to uncommon in Peru.[8]

References

  1. 1 2 BirdLife International (2018). "Thick-billed Siskin Spinus crassirostris". IUCN Red List of Threatened Species. 2018 e.T22720380A132138421. doi:10.2305/IUCN.UK.2018-2.RLTS.T22720380A132138421.en. Retrieved 30 March 2026.
  2. 1 2 Gill, Frank; Donsker, David; Rasmussen, Pamela, eds. (March 2025). "Finches, euphonias, longspurs, Thrush-tanager". IOC World Bird List. v 15.1. Retrieved 23 March 2026.
  3. ↑ Remsen, J. V., Jr., J. I. Areta, E. Bonaccorso, S. Claramunt, D. F. Lane, L, N. Naka, M. B. Robbins, F. G. Stiles, and K. J. Zimmer. Version 27 February 2026. Species Lists of Birds for South American Countries and Territories. South American Classification Committee associated with the International Ornithologists' Union. https://www.museum.lsu.edu/~Remsen/SACCCountryLists.htm retrieved February 28, 2026
  4. ↑ Landbeck, C. L. (1877). "Bemerkungen über die Singvögel Chile's". Der Zoologische Garten (in German). Vol. XVIII. G. Fischer, Zoologische gesellschaft. pp. 254–255. Retrieved March 30, 2026.
  5. ↑ Remsen, J. V., Jr., J. I. Areta, E. Bonaccorso, S. Claramunt, D. F. Lane, L, N. Naka, M. B. Robbins, F. G. Stiles, and K. J. Zimmer. Version 27 February 2026. A classification of the bird species of South America. South American Classification Committee associated with the International Ornithologists' Union. https://www.museum.lsu.edu/~Remsen/SACCBaseline.htm retrieved February 28, 2026
  6. ↑ Check-list of North American Birds (7th ed.). Washington, D.C.: American Ornithologists' Union. 1998. p. 666.
  7. ↑ R. Terry Chesser, Richard C. Banks, F. Keith Barker, Carla Cicero, Jon L. Dunn, Andrew W. Kratter, Irby J. Lovette, Pamela C. Rasmussen, J. V. Remsen, Jr., James D. Rising, Douglas F. Stotz, and Kevin Winker. "Fiftieth supplement to the American Ornithological Society s Check-list of North American Birds". The Auk 2009, vol. 126(3):710–711 retrieved 15 March 2025
  8. 1 2 3 4 5 Schulenberg, T.S.; Stotz, D.F.; Lane, D.F.; O'Neill, J.P.; Parker, T.A. III (2010). Birds of Peru. Princeton Field Guides (revised and updated ed.). Princeton, NJ: Princeton University Press. p. 630. ISBN 978-0691130231.
  9. 1 2 3 4 5 6 7 8 9 10 Clement, P. (2025). Thick-billed Siskin (Spinus crassirostris), version 1.1. In Birds of the World (J. del Hoyo, A. Elliott, J. Sargatal, D. A. Christie, E. de Juana, and M. G. Smith, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.thbsis1.01.1 retrieved March 30, 2026
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