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. 



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