BOSTON PUBLIC GARDEN 27 



rives in another general migratory flight. 

 The arrivals of birds of any species are 

 thus periodical rather than regular nightly 

 during the migration-period of the species. 

 Location and number of birds constitut- 

 ing the flocks present, both of which data 

 prove in very many instances to be quite 

 fixed factors, experience has shown, serve 

 as bases for concluding that the rule is 

 periodicity of arrival and not daily regu- 

 larity. 



It has been found, also, that in an aviary 

 such as the Public Garden provides the 

 birds may be discovered and identified suc- 

 cessfully under rainy conditions, when an 

 umbrella is required to save the observer 

 from a drenching and keep the field-glasses 

 clear for use. Such a day was May 19, 1900. 

 During the whole forenoon, when workmen 

 were obliged to leave their work on account 

 of the steady fall of rain and only those 

 who needed to pass through the Garden 

 moved on its paths, the hunt was success- 

 fully pursued. Thirty species of migrant 

 birds were recorded, while the number of 



