104 BIRD STUDIES WITH A CAMERA 
Swallows are not known to migrate by night, 
and, so far as I am aware, no single Swallow has 
ever been found among the thousands of night- 
flying birds which have perished by striking light- 
houses. The Swallows, therefore, when migrating 
1. Immature Tree Swallows gathering nesting material. 
Or 
probably leave the marsh during the day, but in 
what manner who can say ? 
Several times when crossing the marshes on the 
cars I have observed gatherings of Swallows which 
made the immense flocks observed daily in August 
