Some of the more recent experimental work on bird navigation has been with astronomical (sun) and celestial (star) directional clues. Studies by Kramer, Sauer, and others have indicated a phenomenal inherited ability in birds to use the position of the sun by day and the stars by night to chart their courses. This involves an intricate compensation for daily, seasonal, and geographical changes in the positions of these heavenly bodies. Kramer (1957, 1961) placed diurnal migrants in circular cages and "changed" the position of the sun with mirrors. The birds shifted their position to compensate for these changes. Sauer (1957, 1958), in a fascinating study with nocturnal migrant warblers, placed birds in a round cage open to the sky. These birds oriented in the normal direction for that locality and time of year. He next placed the cage and birds in a planetarium and projected overhead the night sky star patterns for different seasons and localities. The familiar star pattern produced a normal orientation but an unfamiliar sky caused confusion and complete disorientation. These experiments, begun in Germany, are still continuing in other countries with other species. Emlen (1969) used photoperiod manipulation to change the physiological states of spring and fall migratory readiness in indigo buntings. Half the sample of birds were in breeding condition whereas the other half were already past the reproductive stage even though it was spring "outside." When these birds were subjected to a spring star pattern in a planetarium, the birds in spring condition oriented northward but those in autumnal condition oriented southward. Although some results have been negative, by and large the evidence supports the original findings that the sun and stars are visual "landmarks" used by at least some birds as well as bees and probably many other creatures in finding their way home as well as to their winter and summer quarters. In conclusion, then, we can say this about bird orientation and navigation: 1) many cues are available to birds for migratory guidance and one or several of these may be used by any migrant; 2) different species and groups of birds use different cues, depending on their migration traits; 3) visual cues probably play a predominant role in migration (radar studies have indicated that some birds can maintain their orientation even under completely overcast nights, although they usually become disoriented under such conditions); and 4) long-distance migrants and pelagic species have a much higher developed sense of orientation than those species that migrate only short distances or not at all. =INFLUENCE OF WEATHER=