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Inhalt: I. Zur Klärung des Begriffs S. 50. — II. Was ist bis jetzt über Sexualprägung bekannt? S. 53. — III. Methode S. 54. — IV. Paarbildung und Paarverhalten, besonders bei der Stockente S. 57. — V. Prägungsversuche mit Stockenten — ♂♂, Kontrollen S. 58, Erörterung S. 59. — VI. Prägungsversuche mit Stockenten — ♀♀ S. 61. — VII. Prägung durch Mutter und Geschwister S. 63. — VIII. Wann finden die entscheidenden Eindrücke statt? S. 64. — IX. Wie lange bleibt die Prägung erhalten? S. 67. — X. Prägung von Stockerpeln auf verschiedene Prägungsobjekte S. 71, 1. Pragung auf Anatiden S. 72, 2. Unterschiedliche Prägbarkeit auf verschiedene Anatiden S. 72, 3. Prägung auf Hühner und Bläßhühner S. 76. — XI. Die Prägbarkeit verschiedener Anatiden und anderer Vögel auf Stockenten S. 79, 1. Die Prägbarkeit von Hühnern und Bläßhühnern S. 79, 2. Die Prägbarkeit verschiedener Anatiden S. 81. ‐ XII. Geprägtes und Angeborenes S. 83, Erorterung S. 91. — XIII. Ist Prägung Lernen, Gewöhnung oder tatsächlich frühe Fixierung? S. 92. — XIV. Zur Bedeutung der sexuellen Prägung und ihr Vorkommen in der freien Natur S. 94. — Zusammenfassung S. 98. ‐ Summary S. 100. ‐ Literaturverzeichnis S. 102.

A number of factors affecting the learning processes in laboratory imprinting were examined. Two factors alone explain the degree to which young ducklings learn the characteristics of a given model: the length of exposure to the model, and the endogenous arousal state of the duckling. A third, the effect of muscular exertion is not warranted.The characteristics of some models are more rapidly learned than others, and the significance of this fact for biochemical studies of learning is discussed. In this study ease of learning coincided with innate preference: this suggests the presence of a neural filtering mechanism in the duckling which alters the assimilation of information into the CNS and hence controls both innate preference and lcarnability.The distinctive early writings of Lorenz (1935) provided a clear empirical and theoretical framework for subsequent research on imprinting (see reviews by Bateson, 1966; Mess, 1973; Sluckin, 1964;Smith, 1969). In the imprinting context the learning processes leading to filial attachment in the naive young nidifugous bird occur very rapidly. Knowing how rapidly an attachment to a model is formed is important for evaluating physiological and biochemical studies on the imprinting process. For example, one major criticism of the studies on brain ribonucleic acid (RNA) and protein synthesis during imprinting (Bateson, Horn, & Rose, 1972;Gervai & Csanyi, 1973; Smith. Nott, & Yarwood, 1970) is that the so-called biochemical correlates of learning obtained in these studies require a much longer exposure to the model than is required for obtaining consistent behavioral evidence of learning. The present parametric study of imprinting was designed t o explore a number of behavioral factors relevant to the interpretation and planning of physiological studies of imprinting. It defines an important nonspecific endogenous factor (termed arousal) which has implications for Iless's Law of Effort (1 959). MethodA total of 80 mallard ducklings (Anus platyrhynchos) were used in this experiment. These were selected from approximately twice that number in that ducklings which failed

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