Two hybridizing subspecies of the Flame-rumped Tanager have been in contact for at least 6000 years.
What color do you get when you mix red with yellow? Orange, obviously. This fact cannot only be illustrated by a three-year-old and some water-paint, but also by studying the Flame-rumped Tanager (Ramphocelus flammigerus). This tropical species, which lives in Panama, Colombia, Ecuador and Peru, is classified into two subspecies flammigerus and icteronotus that differ in plumage color. The first one has a deep red color while the second one is bright yellow. And hybrids between the two are -you guessed – orange.
Hybridization between these subspecies (which are sometimes considered separate species) has been known for some time. In 1932, Ludlow Griscom showed that several Tanager species were in fact hybrids between flammigerus and icteronotus. The title of his paper was short but brilliant: “Notes on Imaginary Species of Ramphocelus.”
A few decades later, Charles Sibley – the father of avian hybrid zone studies – traveled to Colombia to study the hybrid zone between the two subspecies. He concluded that hybridization was the result of recent human activities in the region, particularly deforestation and growth of crops:
Present evidence indicates that the cutting of the virgin forest from the western slopes of the Western Andes permitted the two types to come into secondary contact after a period of isolation during which the observed differences evolved.
Not So Recent Contact
In a recent study, Andrea Morales-Rozo and colleagues revisit this case by sampling different hybrid zones in Colombia. Based on genetic analyses and modelling of historical distributions, they show that Sibley was partly correct. The two subspecies probably came into contact about 6000 years ago following an expansion of flammigerus. Recent human activities might have contributed to hybridization.
Although our analyses suggest that climatic conditions were suitable for contact between these forms thousands of years prior to major human-caused alterations in the area, it is likely that anthropogenic activities have facilitated contact between them, possibly leading to an increased incidence of hybridization in recent times.
In addition, the hybrid zone seems to have moved to the east and shifted to higher elevations. The reasons for this change are not clear yet. There is still plenty to learn about the Flame-rumped Tanager, but at least we are sure that red + yellow = orange.
Griscom, L. (1932) Notes on Imaginary Species of Ramphocelus. The Auk 49(2), 199-203.
Morales-Rozo, A., Tenorio E.A., Carling M.D. & Cadena C.D. (2017) Origin and cross-century dynamics of an avian hybrid zone. BMC Evolutionary Biology 17, 257.
Sibley, C.G. (1958) Hybridization in Some Colombian Tanagers, Avian Genus “Ramphocelus”. Proceedings of the American Philosophical Society 102(5), 448-453.
The papers have been added to the Thraupidae page.