OCR Text |
Show How BIRDS Prepare for MIGRATION A GERMAN professor. Dr. Thienemann, has recently raised the interesting question as to whether birds which change their placa of abode in spring and fall prepare themselves previously for long Journeys. Such a preparation prepara-tion might conceivably consist of two kinds. It might, on the one hand, include the swallowing of a definite amount of food and. on the other hand, it might consist of some modification in the character of the plumage. In other words do the birds fly with full cropa from which to obtain the necessary energy for their muscular effort, or do they, on the other hand, fly with empty crop and stomach in order to lessen their weightJ Furthermore, Further-more, is there any difference in plumage observ-able observ-able just before the start? . In order to solve the first question, explains The Scientific American Monthly, the learned professor first experimented with caged birds in order to see how much time they required after the taking of food for the crop and stomach to become entirely empty. He found that after feeding feed-ing plentifully, in the majority of cases no trace of food waa left at the end of four hours, in a amaller number eight houra waa required. He then examined birds captured in the act of migration. migra-tion. In these he found that out of 183 individ-nala individ-nala 18 per cent had the crop and stomach full, 40 per cent, had it empty and 42 per cent had it moderately filled. The majority, therefore, a p- peered to endeavor not to overload the stemach. The migratory instinct prevails in general over the hanger instinct Aa to the second question, whether migratory birds exhibit any special care aa to k'" th,r plumage in good condition, he believea that the birds will not refrain from migrating because of injury to the plumage or disorder in it His reservations re-servations seem to prove that the dominant instinct in-stinct in migrating birds is the attempt to proceed. pro-ceed. The stimulus which causes them to seek food is prsctically excluded during the time of the strongest migratory impulse, so thst at times the birds appear almost entirely indifferent even to their fsvorite delicacies; thus the fslcon migrates mi-grates close beside the dove without injury to the latter. |