Abstract: I report an experiment aimed at testing whether foraging efficiency of great tits is limited by light intensity at the time of the dawn chorus. Captive great tits hunting for prey under different luminance conditions were less successful in finding prey when foraging, hunted for a lower proportion of their time, and handled individual prey items for longer when luminance was under approximately 7 cd/m2. This luminance is not reached in the field until after the time of the dawn chorus, suggesting that in the early morning foraging is limited by light intensity. I suggest that a satisfactory functional explanation of the dawn chorus must take into account the comparatively low foraging opportunity early in the morning, as well as the factors affecting the opportunity for singing and other territorial activities.

Abstract: Trial duration and intertrial interval duration were parametrically varied between groups of pigeons exposed to a discrimination involving the presence vs. the absence of a dot. Half the groups received the dot as the positive stimulus (feature positive groups) and half the groups received the dot as the negative stimulus (feature negative groups). Faster learning by the feature positive birds (feature positive effect) was found when the trial duration was short (5 sec) regardless of whether the intertrial interval was short (5 sec) or long (30 sec). No evidence for a feature positive effect was found when the trial duration was long (30 sec) regardless of the length of the intertrial interval (30 sec or 180 sec). The results suggest that short trial duration is a necessary condition for the occurrence of the feature positive effect, and neither intertrial interval nor trial duration/intertrial interval ratio are important for its occurrence. The suggestion that mechanisms underlying the feature positive effect and autoshaping might be similar was not supported by the present experiment since the trial duration/intertrial interval ration parameter appears to play an important role in autoshaping but not the feature positive effect.

Abstract: Boer, Leobert E.M. de, and Jan & Inge Bouman, eds. Genetics and Hereditary Diseases of the Przewalski Horse. Rotterdam: Foundation for the Preservation and Protection of the Przewalski Horse 1979. 176p, several photos and charts. Reproduced from typescript, as issued. Very good paperbound (covers shelf-soiled). ** Publishes 18 papers given at the Arnhem Study-Conference of 1978, on many aspects of breeding Przewalski horses, their behavior, etc.

Abstract: Boer, Leobert E.M. de, and Jan & Inge Bouman, eds. Genetics and Hereditary Diseases of the Przewalski Horse. Rotterdam: Foundation for the Preservation and Protection of the Przewalski Horse 1979. 176p, several photos and charts. Reproduced from typescript, as issued. Very good paperbound (covers shelf-soiled). ** Publishes 18 papers given at the Arnhem Study-Conference of 1978, on many aspects of breeding Przewalski horses, their behavior, etc.