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HOMING ABILITY IN THE NESTLING WILLOW- 

 WARBLEK. 



BY 



J. M. DEWAR, M.D. 



Observations were begun with the object of watching the 

 behaviour of the parent Willow-Warblers {Phylloscopus t. 

 irochilus) when the nestlings are placed on the ground outside 

 the nest. As the first experiment unexpectedly revealed 

 homing ability in the nestling, the original intention was 

 dropped and further trials were made to test for the average 

 capacity of the nestling and for the cues used by it in returning 

 to the nest. 



The surroundings of the nest were well adapted to the 

 purpose in hand. The grass being very short, there was an 

 open space in front of the nest instead of the more usual rank 

 growth of concealing vegetation with one or more runways 

 leading to the nest. The six young in the nest were not more 

 than a few days old. The eyelids were still united, the quills 

 did not project, while the body-tracts were just beginning to 

 show distinctly. All the young looked towards the entrance 

 of the nest. 



1. A chick was taken from the nest and laid down on the 

 turf a foot from and with its head directed away from the 

 entrance to the nest. The chick turned round and crawled 

 back into the nest. 



2. A chick was placed six inches away from the nest, 

 and with its head turned away from the nest. This chick 

 also turned round and crawled towards the nest. But its 

 orientation was not so accurate as in the first case. It came 

 to rest against one side of the nest, where it remained until 

 it was restored to the nest. 



In all cases vision was definitely excluded as a means 

 towards orientation, owing to the eyelids being closed. That 

 the direction of the rays of light acting through the thin 

 eyelids, an odour trail, the odour and warmth of the nest, 

 or auditory cues from the nest or from the parents, did not 

 control orientation is shown by the following tests. 



3. A chick was set down a foot away from and with its 

 head directed towards the entrance of the nest. Its position 

 was thus reversed from that it had occupied in the nest. 

 This chick turned round through an angle of about 130 degrees 

 and crawled farther away from the nest. 



4. A chick was placed three inches from the entrance 



