Granatellus venustus francescae, S. F. Baird, 1865

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 : 20

RED-BREASTED CHAT Granatellus venustus francescae

(vs. G. v. venustus total score 8)

Scored 7 by del Hoyo & Collar (2016) based on the lack of black breast-band of francescae , presence of a white hindcollar, grey of crown extending over nape, tail much longer, and a few additional characters that they did not score. Grant (1965a, based on 29 male and 18 female francescae vs. 24 male and 14 female venustus ) found that the lack of breast-band differentiated 79% of his sample of francescae from 94% of venustus ( Grant 1965a also observed in both taxa that, rarely, a breast-band is present but masked by overlying white feathers). Therefore, this character does not differentiate the taxa completely, and we did not score it, although we believe that it is an important character.

Del Hoyo and Collar (2016) included scores for ‘white hindcollar formed by continuing white postocular stripe (at least 1), grey of crown extending over nape (1)’. We think they assigned two scores for what is essentially a single character ( Fig. 10 ), to which we apply a score of 2.

Whereas del Hoyo & Collar (2016) mention, but did not score, ‘pink of underparts generally slightly paler and less extensive’, Grant (1965a) stated that ‘the majority of both mainland and island samples of adult males had approximately the same amount of red ventrally. A few island specimens were observed to have less, and a few mainland specimens more, than this.’ It is unclear whether this character should be scored. However, we would score the colour of the underparts of immature males; Grant (1965a), based on a sample of perhaps n = 8 vs. n = 6, reported that immature males differ in having almost no red on the underparts in francescae (and in his sample no trace of a black breast-band) vs. much red on the underparts and a complete breast-band (score 2). Based on Grant’s (1965a) data the relative amount of white on the outermost rectrix (measured as the length of the white patch on r6 / length of r6) merits a score of 2, but we conservatively score it 1. Whereas del Hoyo & Collar (2016) afforded a score of 2 for ‘tail much longer’, measurements in Grant (1965a) indicate that the score of 2 applies equally to wing, tarsus and tail lengths, but bill length is shorter (score 1).

Figures

Figure 10. Comparison of the nape and presence / absence of the white hindcollar in male Red-breasted Chat Granatellus venustus: above, Instituto de Biología, Universidad Nacional Autónoma de México specimen of G. v. venustus (Héctor Gómez de Silva); below, G. v. francescae, Isla María Cleofas, May 2016 (Mónica G. Pérez Villafaña)