This species is found in open, lightly wooded habitats, such as hillsides with trees or scrub and forest edges. In South Africa it occurs mainly in coastal areas, inhabiting coastal bush, shrubs along streams, gardens, and areas with rank vegetation. It is not truly migratory, but undertakes some seasonal movements.
The brimstone canary was formerly placed in the genus Serinus but phylogenetic analysis using mitochondrial and nuclear DNA sequences found that the genus was polyphyletic. The genus was therefore split and a number of species including the brimstone canary were moved to the resurrected genus Crithagra.
- C. s. sulphuratus is the nominate race of southwestern and southern Cape Province
- C. s. wilsoni of eastern Cape Province to southern Mozambique is smaller, relatively smaller billed, and paler or more yellowish green than the nominate form. The underparts are entirely yellow.
- C. s. sharpii of northern Mozambique to Kenya is smaller and paler or more yellowish green than the nominate form. Its bill size is intermediate between the other two races.
The brimstone canary is 15–16 cm in length with a heavy bill, which is short, conical and very stout at the base. The bill is light brown with a pinkish or yellowish base. The legs and feet are pinkish-brown. It has yellow-green upper parts with dark green streaking, yellow-green ear coverts and malar stripe, and two yellow wing bars. The underparts are yellow, with a greenish wash on the flanks, and breast. The sexes are similar, but the male is brighter, with a bigger bill, better defined face pattern, brighter yellow wing bars and a greenish rump. Young birds are duller, greyer and less yellow below than the adults.
The degree to which this bird is green or yellow varies considerably across regions. Southern birds are greener than northern birds, even within subspecies, notably with C. s. sharpii. For an overview of finch phylogeny (including canaries) see the entry on finches.
The brimstone canary can be confused with the yellow-fronted canary, but that species is smaller billed with a much more defined head pattern and a bright yellow rump.
The call notes of the brimstone canary in the south of its range are a trilled, deeply pitched swirriwirrit or chirrup. The song is a jumble of chirps, whistles, warbles and trills, with the same deep pitch as the call. Northern birds have a faster, higher, less jumbled and more tuneful version of the song.
The brimstone canary breeds from August to October. The nest is an open cup built from thin stems and other plant material and lined with plant down. It is placed in a leafy bush or a tree.
The brimstone canary is less gregarious than other canaries. It tends to be found singly or in pairs, or occasionally in small groups, and is a common visitor to gardens. It feeds on fruit, seeds, flowers and shoots. Hard seed cases are cracked with the stout bill.
- BirdLife International (2012). "Serinus sulphuratus". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013.
- Zuccon, Dario; Prŷs-Jones, Robert; Rasmussen, Pamela C.; Ericson, Per G.P. (2012). "The phylogenetic relationships and generic limits of finches (Fringillidae)" (PDF). Molecular Phylogenetics and Evolution. 62 (2): 581–596. PMID 22023825. doi:10.1016/j.ympev.2011.10.002.
- Gill, Frank; Donsker, David (eds.). "Finches, euphonias". World Bird List Version 5.2. International Ornithologists' Union. Retrieved 5 June 2015.
- Swainson, William (1827). "On several forms in ornithology not hitherto defined". Zoological Journal. 3: 348.
- Ian Sinclair, Phil Hockey and Warwick Tarboton, SASOL Birds of Southern Africa (Struik 2002) ISBN 1-86872-721-1
- Clement, Harris and Davis, Finches and Sparrows by ISBN 0-7136-8017-2
- SASOL e-guide
- Kenya birds
- Brimstone canary - Species text in The Atlas of Southern African Birds.