Screech-owl

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Screech-owls
Eastern Screech-owl, Megascops asioRufous morph
Eastern Screech-owl, Megascops asio
Rufous morph
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Subclass: Neornithes
Infraclass: Neognathae
Superorder: Neoaves
Order: Strigiformes
Family: Strigidae
Genus: Megascops
Kaup, 1848
Species

Some 20, see text
Synonyms

Gymnasio Bonaparte, 1854
Macabra Bonaparte, 1854

Screech-owls – sometimes written screech owls, especially outside North America – are typical owls (Strigidae) belonging to the genus Megascops. Twenty-one living species are known at present, but new ones are frequently recognized and unknown ones are still being discovered on a regular basis, especially in the Andes. For most of the 20th century, this genus was merged with the Old World scops-owls in Otus, but nowadays it is again considered separate based on a range of behavioral, biogeographical, morphological and DNA sequence data.

Screech-owls are restricted to the Americas. Some species formerly placed with them are nowadays considered more distinct. See below for details.

Contents

[edit] Description

As usual for owls, female screech-owls are usually larger than the males of their species, with owls of both genders being compact in size and shape. The Eastern Screech-owl Megascops asio is one of the smallest species of owls in North America[1]. All of the birds in this genus are small and agile. Screech-owls are generally colored in various brownish hues with usually a whitish, patterned underside, which helps to camouflage them against the bark of trees. Some are polymorphic, occurring in a grayish- and a reddish-brown morph.

[edit] Ecology and behavior

Screech-owls hunt from perches in semi-open landscapes. They prefer areas which contain old trees with hollows; these are home to their prey which includes insects, reptiles, small mammals such as bats and mice and other small birds. Screech-owls have a good sense of hearing which helps them locate their prey in any habitat. They also possess well-developed raptorial claws and a curved bill, both of which are used for tearing their prey into pieces small enough to swallow easily. They usually carry their prey back to their nests, presumably to guard against the chance of losing their meal to a larger raptor.

Screech-owls are primarily solitary. During the late-winter breeding season, however, males make nests in cavities, sometimes reusing abandoned nests of other animals, to try to attract females. The females select their mate based on the quality of the cavity and the food located inside. During the incubation period, the male feeds the female. These birds are monogamous, with biparental care, and only fledge one young per year. The young of most screech-owls are altricial to semialtricial.[2]

Screech-owls are named for their piercing calls. The normal territorial call is not a hoot as with most typical owls, but a trill consisting of more than 4 individual calls per second given in rapid succession. They also have a kind of "song" which is used in courtship and, as a duet, between members of a pair. Calls differ widely between species in type and pitch, and in the field are often the first indication of these birds' presence, as well as the most reliable means to distinguish between species. The distinctness of many species of screech-owls was first realized when vastly differing calls of externally similar birds from adjacent regions were noted.

[edit] Evolution, taxonomy and systematics

The evolutionary relationships of the scops- and screech-owls are not entirely clear. What is certain is that they are very closely related; they may be considered sister lineages which fill essentially the same ecological niche in their allopatric ranges. A screech-owl fossil from the Late Pliocene of Kansas[3] – which is almost identical to Eastern and Western Screech-owls – indicate a long-standing presence of these birds in the Americas, while coeval scops-owl fossils very similar to the Eurasian Scops-owl have been found at S'Onix on Mallorca[4]. The scops-and-screech-owl lineage probably evolved at some time during the Miocene (like most other genera of typical owls), and the three (see below) modern lineages separated perhaps roughly 5 million years ago. Note that there is no reliable estimate of divergence time, as Otus and Megascops are osteologically very similar, as is to be expected from a group that has apparently conserved its ecomorphology since before its evolutionary radiation. Like almost all scops- and screech-owls today, their common ancestor was in all probability already a small owl, with ear tufts and at least the upper tarsus ("leg") feathered.

However that may be, the hypothesis that the group evolved from Old World stock[5] is tentatively supported by cytochrome b sequence data[6]. The screech-owls also have a different placement of the procoracoid (less of an anterior incline) and coracoid bones compared to other New World owls[7].

[edit] 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[8]. 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[6]. Though there was some debate about the reliability of these findings at first[9], they have been confirmed by subsequent studies. In 2003, the AOU formally accepted the genus Megascops again[10].

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.

[edit] Species

Western Screech-owl, Megascops kennicottii
Western Screech-owl, Megascops kennicottii
Rufous- and grey-morph individuals of the Tropical Screech-owl (Megascops choliba)
Rufous- and grey-morph individuals of the Tropical Screech-owl (Megascops choliba)

[edit] Footnotes

  1. ^ Alsop (2001)
  2. ^ Ehrlich et al. (1988): pp.296-298
  3. ^ Specimen UMMP 50982, a partial left coracoid from Fox Canyon: Ford (1966).
  4. ^ Mlíkovský (2002)
  5. ^ Johnson (2003)
  6. ^ a b Heidrich et al. (1995), Wink & Heidrich (1999)
  7. ^ Ford (1966)
  8. ^ Marshall & King (1988)
  9. ^ SACC (2003)
  10. ^ Banks et al. (2003)

[edit] References

Wikimedia Commons has media related to:
  • Alsop, Fred J. (2001): Smithsonian Birds of North America, Eastern Region. Smithsonian Handbooks.
  • Banks, Richard C.; Cicero, Carla; Dunn, Jon L.; Kratter, Andrew W.; Rasmussen, Pamela C.; Remsen, J.V. Jr.; Rising, James D. & Stotz, Douglas F. (2003): Forty-fourth supplement to the American Ornithologists' Union check-list of North American birds. Auk 120(3): 923–931. PDF fulltext
  • Ehrlich, Paul R.; Dobkin, David S. & Wheye, Darryle (1988): The Birder's Handbook. A Field Guide to the Natural History of North American Birds.
  • Ford, Norman L. (1966): Fossil Owls From the Rexroad Fauna of the Upper Pliocene in Kansas. Condor 68(5): 472-475. doi:10.2307/1365319 PDF fulltext DjVu fulltext
  • Heidrich, Petra; König, Claus & Wink, Michael (1995): Molecular phylogeny of the South American Otus atricapillus complex (Aves Strigidae) inferred from nucleotide sequences of the mitochondrial cytochrome b gene. Zeitschrift für Naturforschung C 50(3-4): 294-302. PDF fulltext
  • Johnson, David (2003): The owl pages: Owls in the Fossil Record. Version of 2003-JUL-14. Retrieved 2008-JAN-10.
  • Marshall, Joe T. & King, Ben (1988): Genus Otus. In: Amadon, Dean & Bull, J: Hawks and owls of the world: A distributional and taxonomic list. Proceedings of the Western Foundation of Vertebrate Zoology 3: 296–357.
  • Mlíkovský, Jirí (2002): Cenozoic Birds of the World, Part 1: Europe. Ninox Press, Prague. ISBN 80-901105-3-8 PDF fulltext
  • South American Classification Committee (SACC) (2003): Proposal (#58): Elevate subgenus Megascops (New World Otus) to full generic status. Retrieved 2008-JAN-10.
  • Wink, Michael & Heidrich, Petra (1999): Molecular evolution and systematics of owls (Strigiformes). In: König, Claus; Weick, F. & Becking, J.H. (eds.): Owls: A guide to the owls of the world: 39-57. Yale University Press, New Haven. ISBN 0300079206 PDF fulltext