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Taxonomy change 2016: Colibri thalassinus

By eBird Centroamérica julio 14, 2016

By John van Dort

In a first of a series of portal articles that describe the recent AOU taxonomy changes, which will be implemented in eBird soon, this article briefly treats the split of Colibri thalassinus (Green Violetear) into two species: Colibri thalassinus (Mexican Violetear) and Colibri cyanotus (Lesser Violetear). The proposal for this split was based on a 2015 paper in Zootaxa by Remsen, Stiles, and McGuire that treats the classification of the Polytminae, a subfamily of the Trochilidae. In that paper, the authors argue that the two groups of thalassinus found in Middle America, i.e. the nominate group from Mexico to Nicaragua, and the cyanotus group from southern Middle America and northern South America, differ morphologically as much from each other as either does from other green species in the Colibri genus. Both groups were once considered valid species (Ridgway 1911, Cory 1918), but they were merged by Peters (1945) for no apparent reason. The Zootaxa paper tentatively suggests re-splitting them based on morphological differences, with the admission that the proposal is not based on phylogenetic work, and that they were thus unable to determine whether the thalassinus complex is monophyletic. The AOU’s checklist committee, NACC, sometimes criticized for being too conservative or leaning too much on the crutch of phylogenetics, decided to take what Remsen et al. (2015) present as an “unresolved issue” and went ahead and resolved it: Colibri cyanotus was split off from Colibri thalassinus.

The English common name for Colibri thalassinus used to be Green Violetear; now it is Mexican Violetear, thus becoming the second resident species in Central America with the Mexican moniker, after the Mexican Whip-poor-will was split off from the (Eastern) Whip-poor-will in 2010. Several birds that barely range into the United States were named ‘Mexican’ (Jay, Chickadee, and Whip-poor-will) and now Mexican Violetear joins the ranks. One might wonder whether the NACC would do well to consider retaining the Mexican qualifier for truly Mexican endemics such as Mexican Sheartail, Mexican Hermit, Mexican Woodnymph, and Mexican Parrotlet. The form from southern Middle America that was split off now becomes Colibri cyanotus, Lesser Violetear. In an ideal world, we can compare Lesser and Greater Yellowlegs, or Lesser and Greater Roadrunners. But in this world there is no Greater, only Mexican Violetear…

Lesser Violetear (Colibri cyanotus), 11 June 2016, San José, Costa Rica. Note the absence of violet-blue on the breast and chin. The brown edges on some of the contour feathers suggest this individual is immature. Photo © John van Dort

Lesser Violetear (Colibri cyanotus), 11 June 2016, San José, Costa Rica. Note the absence of violet-blue on the breast and chin. The brown edges on some of the contour feathers suggest this individual is immature. Photo © John van Dort

Separating these new species in the field will not be an issue, as they are entirely allopatric (i.e. no range overlap). The Mexican Violetear occurs from Mexico to Nicaragua, while the Lesser Violetear is found in the highlands of Costa Rica and western Panama, and then again from Colombia to Bolivia. The Nicaraguan Depression divides the two species. The morphological differences include a slight size difference (appreciated in the English common name ‘Lesser’) and a difference in breast coloration: violet-blue in the northern species, green in the southern species. The Mexican Violetear also shows a hint of violet-blue on the chin, a feature that is much more strongly developed in the Sparkling Violetear (Colibri coruscans) of South America, but absent in Lesser Violetear.

Mexican Violetear (Colibri thalassinus), 30 July 2014, near Tegucigalpa, Honduras. Note the violet-blue on the breast and a hint of violet-blue on the chin, features absent in Lesser Violetear. Photo © John van Dort

Mexican Violetear (Colibri thalassinus), 30 July 2014, near Tegucigalpa, Honduras. Note the violet-blue on the breast and a hint of violet-blue on the chin, features absent in Lesser Violetear. Photo © John van Dort

It may be worth noting that taxonomy is a field in constant flux, and that decisions by taxonomic committees only reflect the science current at the time of the decision. As one ornithologist and birder recently pointed out in a social media forum, birders may like to grumble about frequent taxonomy changes, but they should really be glad that there is so much taxonomic attention directed to birds—other taxa receive far less critical scrutiny and are sometimes left unresolved for decades. Remsen et al. (2015) point out that potential vocal and behavioral differences among the various populations of the thalassinus complex may yet lead to discoveries of cryptic species hidden in these two species… And that’s where eBirders have a chance to contribute, by recording song and noting behavior, and include their observations in their checklists.

References:

Cory, C. B. 1918. Catalogue of Birds of the Americas. Field Museum Natural History Publications, Zoological Series, 13 (p. 2, no. 1), 1–315 pp.

Peters, J. L. 1945. Check-list of birds of the world, vol. 5. Harvard University Press, Cambridge, Massachusetts.

Remsen, J. V. Jr., F. G. Stiles & J. A. McGuire. 2015. Classification of the Polytminae (Aves: Trochilidae), Zootaxa 3957 (1): 143–150.

Ridgway, R. 1911. The Birds of North and Middle America. Bulletin United States National Museum, No. 50 (pt. 5) 859 pp.

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