Amazilia rutila graysoni, Cinnamon Hummingbird, 2013

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 : 19-20

CINNAMON HUMMINGBIRD Amazilia rutila graysoni

(vs. A. r. rutila total score 7)

Scored 4 by del Hoyo & Collar (2014) based on larger size in all external measurements (to which they assign a score of 3) and slightly ‘darker and duskier’ plumage (which they score 1). Regarding colour differences, Grant (1965a, based on 27 male and 18 female graysoni vs. 46 male and 14 female rutila ) stated that the underparts are uniformly dark cinnamon vs. paler cinnamon, particularly on the chin and throat. The belly of some mainland rutila at IBUNAM is as dark as the underparts of graysoni , but the chin and throat, and often asymmetrical patches on the breast, are always paler ( Fig. 9 ). Grant (1965a) also mentioned that the upperparts are ‘dark green or even red-bronze’ vs. ‘paler green, and in those which have a bronze colour it is always yellow-green, never red’, and that the ‘tips’ (sic, actually, subterminal portions) of most, particularly the outer, rectrices are dark greenish bronze to dull violet in 90% of graysoni vs. paler, bright greenish bronze in 90% of rutila specimens (score at least 1). The underpart colours in these taxa are based on the intensity of cinnamon pigmentation whereas the upperpart colours (as in iridescent colours of hummingbirds generally) are based on a combination of melanin and feather nanostructure; therefore we score 1 for underparts colour and 1 for upperparts colour.

Grant’s (1965a) measurements reveal that the bill in graysoni is both relatively shorter (effect size for bill length 2 vs. effect size for most external measurements 3 [score 1]) and, especially in males, relatively narrower (effect size for bill width 1 but for bill length 2 [not scored]).

The notably larger overall size of insular graysoni is paralleled by Rufous-tailed Hummingbird Amazilia tacatl handleyi of Isla Escudo de Veraguas, Panama ( Wetmore 1959, Miller et al. 2011) but in the later case, there is reportedly a narrow ‘zone of morphometric intergradation’ ( Weller 1999), although the data on which the statement was based have not been published to date. There is no zone of intergradation between graysoni and mainland rutila .

Of the 12 specimens of graysoni at IBUNAM, the smallest (P019069 from Isla María Madre) has atypical upperparts, with much-reduced iridescence on the wing-coverts and back compared to either graysoni or rutila . We consider that this specimen could be a hybrid graysoni × rutila , the colour of its upperparts being heterotic (a trait of a hybrid outside the range of variation for that trait in either parental species; McCarthy 2006: 17).

Figures

Figure 9. Two specimens of Cinnamon Hummingbird Amazilia rutila graysoni (below) compared with two specimens of A. r. rutila (above); note the considerable difference in size. The second specimen from the top is the darkest-throated A. r. rutila at Instituto de Biología, Universidad Nacional Autónoma de México; the right side of its throat is paler than the left, and thus more like the typical colour of the subspecies (Héctor Gómez de Silva)