Produced by Chris Curnow, Joseph Cooper, Josephine Paolucci and the Online Distributed Proofreading Team at http://www.pgdp.net. THE POSTNATAL DEVELOPMENT OF TWO BROODS OF GREAT HORNED OWLS (Bubo virginianus) BY DONALD F. HOFFMEISTER AND HENRY W. SETZER University of Kansas Publications Museum of Natural History Volume 1, No. 8, pp. 157-173 October 6, 1947 UNIVERSITY OF KANSAS LAWRENCE 1947 UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY Editors: E. Raymond Hall, Chairman, Donald S. Farner, H. H. Lane, Edward H. Taylor Volume 1, No. 8, pp. 157-173 October 6, 1947 UNIVERSITY OF KANSAS Lawrence, Kansas PRINTED BY FERD VOILAND, JR., STATE PRINTER TOPEKA, KANSAS 1947 21-6958 The Postnatal Development of Two Broods of Great Horned Owls (_Bubo virginianus_) By DONALD F. HOFFMEISTER AND HENRY W. SETZER Opportunity regularly to observe at the nest the development of young Great Horned Owls, _Bubo virginianus_ (Gmelin), under favorable conditions, was afforded when a pair nested and reared their three offspring in 1945 and one offspring in 1946 on the vine-covered north wall of the Museum of Natural History at the University of Kansas. The observations here reported are based primarily on the three young raised in 1945 when daily observations were made. These have been supplemented by other observations made of the one nestling in 1946. Unless otherwise stated, observations pertain to the nest and three young in 1945. NEST SITE In 1945 the nest was situated on a metal-covered cement ledge, two feet wide and 48 feet above the ground, at the northeast corner of the Museum Building. The nest was protected on the east by a stone abutment of the building and on the south by the north wall of the building itself. Here the nest could be observed at will through a laboratory window without disturbing the birds. The taking of notes was begun at the time of egg-laying and extended to the time at which the young left the nest, February 3 through April 26, 1945. In 1946 the owls nested farther down the north side of the building, behind two cement pillars, approximately 25 feet above the ground. To examine the nest in 1946 it was necessary to lower an observer down the side of the building by means of a rope. Observations of this nest were never made more frequently than every other day. The adult owls were first seen at the nest on February 3, 1946; careful examination of the nest began when the one egg hatched on March 7 and continued until April 25, shortly before the young owl left the nest.