EVENING GROSBEAK. 50 



like New England which is so far from its usual habitat, 

 also so distant from the usual limit of its w^inter wanderings, 

 presents an interesting problem. This movement eastward 

 cannot be called migratory, as the term is generally applied 

 to those birds which perform annual journeys from north to 

 south, and from south to north, which are governed wholly by 

 food supplies. It is highly probable that this and similar 

 movements among birds and other animals, arise from the 

 overproduction of a given species under peculiarly favorable 

 conditions which have existed for a limited season. This over- 

 crowding of a given section would, to be sure, in a measure, 

 tend to exhaust the food supply of that section, and thus give 

 rise to an impulse which would revive a nearly lost migratory 

 instinct which was once possessed by at least all birds and 

 possibly some mammals. The revival of this instinct causes 

 the animal in which it is revived to wander from its birth- 

 place, to which it may never return again : in which case the 

 overcrowded district would be relieved. ( For further remarks 

 upon this interesting subject, see notes on Migration of Birds 

 and other Animals, in Contributions to Science, Vol. Ill, page 

 45). 



Song. The Evening Grosbeak has a loud call note, which it 

 utters quite frequently, and a short but not very pleasing 

 warble. 



The vocal organs are quite peculiar. These are figured on 

 page 5. In regard to the sound producing membrane, we find 

 that the tympaniform membranes, f, v, are considerably re- 

 duced in size ani are vibratory only on the upper triangular 

 portion, v, but that there is an additional vibrating space be- 

 tween the upper bronchial half ring, seen just above v, which 



