Setophaga pitiayumi insularis (Lawrence, 1871)

Silva, Héctor Gómez de, Pérez Villafaña, Mónica G., Cruz-Nieto, Javier & Cruz-Nieto, Miguel Ángel, 2020, Are some of the birds endemic to the Tres Marías Islands (Mexico) species?, Bulletin of the British Ornithologists’ Club 140 (1), pp. 7-37 : 31-32

TROPICAL PARULA Setophaga pitiayumi insularis

(vs. S. p. pulchra)

Coloration.—Reddish-tinged vs. pale buff flanks (score at least 1), much less white on outer rectrix (score 1), no or scatered black feathers at base of culmen vs. entirely black ‘culmen bridge’ feathers (score 2). Additionally, only the outer pair or two of tail feathers have white in 100% of insularis (both sexes) vs. three outer tail feathers in 82% of male and 73% of female pulchra (not scored) (from Grant 1965a, based on 42 male and 20 female insularis from the Tres Marías, and 11 male and eight female insularis from the mainland vs. 23 male and 12 female pulchra).

Morphometrics.—Larger in all external measurements, especially the longer tarsus in males and longer tail in females (both score 3, although this seems suspiciously high because these differences are not immediately evident to the eye) but bill in females shorter (score 1).

Reasons for uncertainty.—Race insularis also occurs in mangroves in mainland Nayarit ( Grant 1965a), and there is a specimen from Labrados, Sinaloa ( McLellan 1927) and records from Todos Santos and El Oro, Baja California Sur ( Iliff et al. 2008). Hybrid insularis × pulchra have been documented at Peñita de Jaltemba ( Grant 1965a, two specimens that combine the flanks colour of insularis with the wing length of pulchra and are intermediate in tail and / or tarsus length) and San Blas ( Iliff et al. 2008, four specimens with intermediate measurements). Also, Grant (1965a: 52) noted that his sample of mainland insularis somewhat approached pulchra in frequency of different tail paterns, and possibly also in some mensural characters, suggesting introgression. Hybridisation may be extensive where they are parapatric. Furthermore, it is also unclear if phenotypic characters differentiating insularis may partially bridge the gap between S. p. pulchra and race graysoni from Socorro Island. Tail length of insularis is much closer to graysoni than pulchra ( Ridgway 1902; under Socorro Parula , del Hoyo & Collar 2016 cite mean tail lengths for male insularis and pulchra that are too short, cf. Ridgway 1902).

In plumage, adult graysoni generally resembles juveniles of other races of S. pitiayumi . However, there may be a stepped cline in the percentage of adults with juvenile-like plumage; insularis is intermediate in proportions and especially the extent of black in the lores and orbital area ( Grant 1965a: 38). Also, while black is usually thought to be completely absent in the face of graysoni, Baptista & Martínez-Gómez (2002: 38) found that a small percentage of individuals do show some black. There may also be a cline in the extent of white in the rectrices between pulchra, insularis and graysoni (Regelski & Moldenhauer 2012) .

All of the above indicates that graysoni is perhaps not as phenotypically distinct from pitiayumi as scored by del Hoyo & Collar (2016) who considered graysoni to be a separate species, while simultaneously overlooking one important character of graysoni that sets it apart from the rest of S. pitiayumi , namely the grey of the face extends to include the malar in graysoni (as in Northern Parula S. americana ) vs. the yellow of the throat extends up to include the malar in pitiayumi including insularis ( Dunn & Garret 1997, Iliff et al. 2008). Also, del Hoyo & Collar (2016) tentatively added a score of 2 to the diagnosis of graysoni based on a ‘more complex voice, involving several songs, resembling those of S. ruticilla , S. pensylvanica and S. americana ’ while insularis apparently has a similar varied repertoire (HGdS pers. obs.). Furthermore, S. pitiayumi (with or without graysoni ) may be paraphyletic with respect to S. americana ( Lovete & Bermingham 2001, Evans et al. 2015). The situation is clearly very complex and requires further study, including testing the extent of introgression / hybridisation of insularis and pulchra on the Nayarit (and Sinaloa?) mainland, and a phylogeographic study of S. pitiayumi (sensu lato) with samples from throughout the species’ range.