Melanotis caerulescens longirostris

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 : 25

BLUE MOCKINGBIRD Melanotis caerulescens longirostris

(vs. M. c. caerulescens total score 4)

Coloration.—Based on 52 male and 24 female longirostris vs. 29 male and 32 female caerulescens, Grant (1965a) found that ‘less than half’ of longirostris were paler in the throat and crown feathers than ‘most’ of his caerulescens sample but the palest specimens of each were indistinguishable. Therefore there is large overlap (no score).

Morphometrics.—Slightly larger but has proportionately much longer bill in both sexes (score 2) whereas the tail is shorter, especially in males (score 2). Additionally, Grant (1965a) found that coracoid length may be shorter in island birds but did not provide sufficient information to calculate effect size because he considered his sample to be inadequate (three male and six female longirostris vs. five male and two female caerulescens ). However, the measurement ranges have slight to no overlap, which suggest the difference is not minor (not scored).