EXTERNAL VALIDITY AND EXPERIMENTAL-DESIGN - THE SENSITIVE PHASE FOR SONG LEARNING

In the past decade there has been widespread acceptance of the idea th at the use of live, socially interactive tutors in song learning exper iments produces results that differ dramatically from, and are more va lid than, results obtained with tape, tutors. The influential series o f experiments by Baptista & Petrinovich (1984, Animal Behaviour, 32, 1 72-181, 1986, Animal Behaviour, 34, 1359-1371; Petrinovich Sr Baptista 1987, Animal Behaviour 35, 961-974) have promoted this view, and thei r results have been widely accepted. Baptista & Petrinovich's results have led them and others to question whether there are age-limited sen sitive phases for song learning, as Marler's (1970, Journal of Compara tive Physiology and Psychology Monographs, 71, 1-25) early studies an the white-crowned sparrow, Zonotrichia leucophrys; suggested, and led them to argue that interactive tutoring produces essentially open-ende d learning. I argue here that this view is mistaken, and that the sens itive phase for song learning in the white-crowned sparrow is identica l for live and tape tutors and is restricted to the first few months o f life,:Baptista Sr Petrinovich presented live and tape tutors for dif ferent periods to their subjects. Type of tutor (live versus tape);is confounded with duration of exposure to tutors. As a consequence, thei r experiments confound: two different forms of song learning that occu r at different ages, and give the mistaken appearance of an extended s ensitive phase when Live tutors are used. (C) 1998. The Association fo r the Study of Animal Behaviour.