Barn Owls and Such

European barn owl Tyto alba, photographed by Nuno Barreto.

I have no idea where the 'wise old owl' stereotype originally came from. Perhaps it simply originated from their appearance: their broad faces, sedate manner, and slightly supercilious half-lidded gaze (those last two, of course, only applying under the circumstances most people would actually see an owl: as a half-asleep night-dweller rudely awakened during the day). Whatever the cause for their associations, owls are one group of birds that have commonly featured in popular culture. The Eurasian barn owl Tyto alba is one owl species that has long held a particular association with humans. Owls mostly do not build their own nests, but make use of suitable hollows and crannies that they find ready-made. The preferred food of barn owls is small mammals such as rats and mice (though they will not turn up their beaks at alternative fare such as reptiles or large insects when their favourite is not available). Put these two facts together, and human constructions (i.e. barns) can be paradise for a barn owl: ready-made secluded nesting spots in the roof-space, and a steady supply of rodents attracted to stored foodstuffs and/or refuse.

Greater sooty owl Tyto tenebricosa arfaki, photographed by Nik Borrow.

The European barn owl is just one species in the genus Tyto, within which König & Weick (2010) recognised 25 species from around the world. While some Tyto species, like T. alba, are found over a wide range, others are found in restricted localities (many on particular oceanic islands). Some are very poorly known: the Taliabu masked owl Tyto nigrobrunnea from Indonesia was described from a single specimen in 1939, with only a handful of sight records since to attest to its continued existence. The Itombwe owl Tyto prigoginei of central Africa was similarly unknown between its initial description in 1952 and the mistnet capture of a live female in 1996. Prior to its transfer to Tyto by König & Weick (2010), this last species was included in the genus Phodilus, the bay owls, which is the living sister group to Tyto. Together, these two genera form the family Tytonidae, separate from all other owls in the family Strigidae. Tytonid owls differ from strigid owls in a features such as having the inner and central toes of the foot similar in length (versus the inner toe being distinctly shorter than the central one in strigids), with the central toe being serrated on the underside. The species of Tyto have a distinctly heart-shaped facial disc (that of Phodilus species is almost reminiscent of Hello Kitty). Many Tyto species, such as T. alba, prefer open habitats, but some, such as the sooty owls Tyto multipunctata and T. tenebricosa of eastern Australia and New Guinea, inhabit rainforests. The smallest Tyto species are T. prigoginei at about 24 cm total length and the Galapagos barn owl T. punctatissima at about 26 cm, and the largest is the Tasmanian grass owl T. castanops, reaching up to 55 cm in length and about 1.25 kg in weight.

Tasmanian grass owl Tyto castanops, photographed by Murray Lord.

Other extinct species would have also probably broken the 1 kg mark. Tyto species have a long fossil record, going back to the Middle Miocene European species T. sanctialbani (Kurochkin & Dyke 2011). Tytonids of now-extinct genera had been abundant in Europe before that time, but Mlíkovský (1998) suggested that they had become temporarily extinct there in the Early Miocene, owing to a gap in the fossil record. Tyto sanctialbani was similar in size to the modern T. alba (Mlíkovský 1998), but a number of giant fossil barn owls are known from islands around the world. The largest include Tyto pollens and T. riveroi in the West Indies (the Bahamas and Cuba, respectively), and T. robusta and T. gigantea from Gargano. Gargano is a peninsula of southern Italy that was a separate island during the Late Miocene to Early Pliocene, at which time it was home to a distinctive endemic fauna including such animals as the absolutely insane small ruminant Hoplitomeryx, which possessed both a crown of five spike-shaped horns and long dagger-like canines. It has been suggested that this over-exuberant armature had evolved as a defence against Gargano's main predators, an assemblage of raptors including the aforementioned Tyto species. The larger of the two, T. gigantea, was about twice the size of a living European barn owl, and perhaps larger than any living owl (Ballmann 1976), though it was more gracile in build than the largest living Bubo species. Ballmann provides measurements for leg bones of T. gigantea and not wing bones, but if we assume similar proportions to a modern barn owl then we'd be looking at a wingspan for T. gigantea of about two metres. That, I submit, is enough to scare seven colours of crap out of any number of small mammals.

REFERENCES

Ballmann, P. 1976. Fossile Vögel aus dem Neogen der Halbinsel Gargano (Italien), zweiter Teil. Scripta Geol. 38: 1-59, 7 pls.

König, C., & F. Weick. 2010. Owls of the World, 2nd ed. Christopher Helm: London.

Kurochkin, E. N., & G. J. Dyke. 2011. The first fossil owls (Aves: Strigiformes) from the Paleogene of Asia and a review of the fossil record of Strigiformes. Paleontological Journal 45 (4): 445-458.

Mlíkovský, J. 1998. A new barn owl (Aves: Strigidae) from the early Miocene of Germany, with comments on the fossil history of the Tytoninae. J. Ornithol. 139: 247-261.