CLIFF-RESPONSE BEI TROTTE L LU M ME N 



1143 



SUMMARY 



Guillemot chicks usually grow up on narrow, exposed cliff ledges. When they 

 are 18-25 days old, before having attained their full flying ability, they jump from 

 the high rock face. The behavioural adaptations protecting the chick from falling 

 and their altération at fledging time are the subject of this study. 



Field observations reveal, that wild Guillemot chicks spend 95% of their 

 flrst days of life protected under one of the parent birds. 



Exposed chicks, left by the parent, always move from the edge of the précipice 

 to the rock wall. 



Experiments with 250 incubator-hatched and hand-reared Guillemot chicks 

 indicate the following: Newly hatched chicks show a pronounced négative photo- 

 taxis. This leads them from the précipice to the rock wall. 



They show a distinct need for physical contact. This is satisfied between body 

 and wing of the parent bird. In the parents' absence the possibility for contact 

 with the wall may attract the chick. 



Three-day-old, inexperienced birds are able to perceive a précipice optically and 

 avoid it. 



Sixteen wild chicks, tested at fledging âge, showed a positive phototaxis. During 

 development their response to light relationships on the ledge has changed, thus 

 providing one of the conditions for leaving the clifT. 



LITERATUR 



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