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Photographs on this web-site were taken by Paul Smith, Hemme Batjes, Regis Nossent,
Alberto Esquivel, Arne Lesterhuis, José Luis Cartes, Rebecca Zarza and Hugo del Castillo and are used with their permission.
TYTONIDAE - BARN OWLS
A single species with an almost cosmopolitan distribution reaches Paraguay. Though the European subspecies are the most well-studied of the Strigiformes other subspecies and species are almost unknown. Globally it is likely that more than one species is involved in what is currently recognised as Tyto alba. It is classified in the subfamily Tytoninae. This family was apparently more diverse than the Strigidae during the Paleocene, but have been surpassed by them in species numbers in more modern times.
Barn Owls have a large, rounded head and tapering body. The eyes are forward-facing but smaller than in true owls. They are characterised by their pale plumage and heart-shaped facial disk with a rim of stiff feathers. This rim serves to amplify sound when hunting at night. Location of prey items is further enhanced by the asymmetrical location of the external ears, the left being higher than the right, to help pinpoint the source of noise. Barn Owls have an elongated, compressed bill and long legs feathered on the posterior side. The inner toe is the same length as the middle toe and the middle claw is pectinated. They have 10 primaries and the two outermost are of similar length. The tail is short, emarginated and square. Wings are long and broad increasing lift and allowing slow flight without stalling. Low wing loading allows them to lift heavy prey and carry it slowly without a need for a massive increase in energy consumption. Silent flight is assisted by the leading edge of the flight feathers being stiff and comb-like to reduce noise, the trailing edge being soft and hair-like to reduce turbulence and all wing feathers having a downy surface to reduce noise made by feather contact during flapping. Skeletally the hind margin of the sternum is complete, the sternum has two notches and the furcula is joined to the keel of the sternum. Timing of moult is influenced by food supply and the outer primaries are replaced more rapidly than the other flight feathers. Vocalisations are otherworldly, consisting of shrieks, clicks and hisses. Females are larger than males.
REFERENCES
Bruce MD RB 1999 - Tytonidae Handbook of the Birds of the World Volume 5 - Lynx Ediciones.
Campbell B & Lack E 1985 - A Dictionary of Birds - T & AD Poyser.
Konig C, Weick F, Becking JH 1999 - Owls: A Guide to the Owls of the World - Pica Press.
