Screech-owl - Evolution, Taxonomy and Systematics - The Splitting of Otus Sensu Lato

The Splitting of Otus Sensu Lato

While late-19th-century ornithologists knew little of the variation of these cryptic birds which often live in far-off places, with every new taxon described a few differences between the Old and New World "scops" owls became more and more prominent. Namely, the scops owls give a whistling call or a row of high-pitched hoots with fewer than four individual hoots per second. This call is given in social interaction or when the owl tries to scare away other animals. The screech owls on the other hand are named for their piercing trills of more than four individual notes per second and as noted above they also have a kind of song, which is absent in the scops owls. There are a few other differences such as brown coloration below being common in scops-owls and almost never seen in screech owls, but the difference in vocalizations is most striking.

By the mid-19th century, it was becoming clear that Otus encompassed more than one genus. First, in 1848, the screech owls were split off as Megascops. Subsequently, the highly apomorphic White-throated Screech Owl of the Andes was placed in the monotypic genus Macabra in 1854. Gymnasio was established in the same year for the Puerto Rican Screech Owl, and the Bare-legged Owl (or "Cuban Screech Owl") was separated in Gymnoglaux the following year; the latter genus was sometimes merged with Gymnasio by later authors.

By the early 20th century, the lumping together of taxa had come to be preferred. The 3rd edition of the AOU checklist in 1910 placed the screech owls back in Otus. Although this move was never unequivocally accepted, it was the dominant treatment throughout most of the 20th century. In 1988 it was attempted to resolve this by reestablishing all those genera split some 140 years earlier at subgenus rank inside Otus. Still, the diversity and distinctness of the group failed to come together in a good evolutionary and phylogenetic picture, and it was not until the availability of DNA sequence data that this could be resolved. In the mid-to-late 1990s, preliminary studies of mtDNA cytochrome b across a wide range of owls found that even the treatment as subgenera was probably unsustainable and suggested that most of the genera proposed around 1850 should be accepted. Though there was some debate about the reliability of these findings at first, they have been confirmed by subsequent studies. In 2003, the AOU formally accepted the genus Megascops again.

It was also confirmed that the Bare-legged Owl was distinct enough to warrant separation in its own genus. The Puerto Rican Screech Owl, however, is just a slightly aberrant Megascops. Furthermore, the White-throated Screech Owl was recognized as part of an ancient lineage of Megascops – including also the Whiskered Screech Owl and the Tropical Screech Owl which previously were considered to be of unclear relationships – and indeed its call structure is not too dissimilar from the latter. Its distinct coloration, approximated in the Southern Whiskered Screech Owl (Megascops trichopsis mesamericanus), is thus likely the result of strong genetic drift.