Restoring the species status of Catharus maculatus (Aves: Turdidae), a secretive Andean thrush, with a critique of the yardstick approach to species delimitation

Abstract

In the 1850s, two species of "Spotted" Nightingale-Thrush (Aves: Catharus) were independently described from montane rainforests of Guatemala, C. dryas (Gould, 1855) and Ecuador, C. maculatus (Sclater, 1858). However, due to similarities in plumage color, C. maculatus was reclassified as a subspecies of C. dryas in 1878, a decision that has been upheld for 137 years. We collected multiple lines of evidence including phylogenetic analysis of mitochondrial DNA sequences (ND2), discriminant and principal components analysis of morphometric and vocal data, and statistical modeling of ecological niches, that collectively indicate that C. d. dryas and C. d. maculatus are independent species. We recommend restoring species status to C. maculatus of South America and applying the common name Sclater's Nightingale-Thrush to this species.En los años 1850s, dos especies de "zorzalito" (Aves: Catharus) fueron descritas en las selvas montañosas de Guatemala, (C. dryas Gould, 1855) y Ecuador, C. maculatus (Sclater, 1858). Sin embargo, debido a la similitud en el color del plumaje, en 1878 se reclasificó a C. maculatus como una subespecie de C. dryas, una decisión que se ha mantenido por 137 años. A través de múltiples líneas de evidencia, incluyendo un análisis filogenético con secuencias de ADN mitocondrial (ND2), análisis discriminantes y componentes principales de los datos morfométricos y vocales, y modelos estadísticos de nichos ecológicos, encontramos que colectivamente estos resultados sugieren que C. d. dryas y C. d. maculatus son especies independientes. Recomendamos regresarle el nombre taxonómico de C. maculatus a la especie de América del Sur.

Are some of the birds endemic to the Tres Marías Islands (Mexico) species?

“…The Tobias et al (2010) criteria and del Hoyo & Collar (2014, 2016 have been praised for their consistency and transparency, and for using effect size rather than statistical significance (e.g. Winker 2010, Brooks & Helgen 2010, Patten 2015, but other aspects have been criticised (Remsen 2015, 2016, Halley et al 2017; although note defence by Collar et al 2015). Perhaps the most significant negative criticism by Remsen (2015Remsen ( , 2016 concerned the treatment of cases with extensive hybridisation along a broad hybrid zone.…”

“…This criticism is not pertinent here because most of the Tres Marías endemics are not in parapatry, and there is little or no hybridisation with their mainland counterparts, with the possible exception of Setophaga and Turdus. The strongest criticism by Halley et al (2017) of using a threshold of divergence to decide if a taxon deserves species status is that it can be unclear which is the relevant taxon for comparison. For the species discussed here, except perhaps Northern Cardinal Cardinalis cardinalis, the sister taxon is unquestionably the population on the adjacent mainland, and Grant (1965a) was careful to use that population as a basis for comparison.…”

The misidentification of Turdus ustulatus Nuttall, and the names of the nightingale-thrushes (Turdidae: Catharus)

“…Recently, the American Ornithological Society North American Classification Committee addressed a similar problem in hummingbirds by voting to 'standardize the English group name of all species of Lampornis to Mountain-gem and reduce the prevalence of the English group name 'hummingbird' across the family, thereby strengthening the association of these species with other species of Lampornis and emphasizing their distinctness relative to other species in the Trochilidae' (Chesser et al 2019: 7). Following that example, I propose that the common names of the migratory species of Catharus be revised to 'strengthen Halley et al (2017). The ordering of species according to phylogenetic clades (A-C) follows Voelker et al (2013) and Everson et al (2019).…”

Measuring evolutionary independence: A pragmatic approach to species classification

“…To illustrate the measurement approach to species delimitation, the remainder of this section will briefly present one such yardstick method, namely, the Tobias criterion (Tobias et al 2010). 3 Note that I choose the Tobias criterion to illustrate the measurement approach because it is relatively simple, has received wide attention from both taxonomists and users of taxonomy (Remsen 2016;Burfield et al 2017;Halley et al 2017), and has been adopted in practice by the prominent organization Birdlife International for their species checklist (Hoyo and Collar 2014). It is not my aim to defend the Tobias criterion as the best method of species delimitation or even the most promising approach to measuring evolutionary independence.…”