200 Tyler, Simultaneous Action. [aptU 



which a signal could best be heard, — very few birds make up the 

 flock and all could hear the signal, but instead of simultaneous 

 action there is individual alarm. 



It is possible that fear may be communicated throughout a large 

 flock by any one of their number starting up in alarm, but that this 

 explanation is always, or even often, responsible for the uprisings 

 is improbable on account of the regularity of the retreats to cover. 



The behavior of the individuals composing a flock of Sparrows, 

 as opposed to their movements " en masse " is well seen if one slowly 

 approaches a flock at rest in shrubbery. Now, the birds gradually 

 withdraw; each bird as he feels himself in danger, retreats. He at 

 first hops deeper into the bushes and later, perhaps, flies. One 

 bolder than the others, may remain alone near the danger even after 

 the others have flown. Under these circumstances the birds act 

 just as one would expect any company of individuals to act at the 

 approach of danger; — when threatened each individual seeks 

 safety. It is true that in the movements as a body, each individual 

 may be seeking safety, but here there is a difference; each bird in a 

 large flock starts at the same instant and, until perched, acts ex- 

 actly as his companions do. It is possible that sometimes the birds 

 are really frightened away, but, in that case, they act as if they all 

 perceived the danger and reacted to it as a unit. This instant re- 

 sponse is clearly distinct from the straggling retreat from a passing 

 carriage. 



I was interested to note, some time ago, the behavior of a large 

 flock of birds collected in an open field with no cover near. Al- 

 though the birds were not House Sparrows, they belonged to species 

 in which the habit under consideration is well marked. The note 

 indicates that the proximity of shelter, which might act as a stimu- 

 lus to retreat, is not responsible for the interruptions while feeding. 

 "Feb. 7, 1911. Twenty Goldfinches and more than twice as many 

 Redpolls are feeding on the snow upon weed-seeds. This large 

 flock of nearly a hundred birds is spread out over half an acre of 

 meadow land where the weed stalks, sticking thickly through the 

 snow, afford abundant food. In spite of the plentiful supply of 

 food, the birds are restless and keep starting up and alighting at 

 once near by, but there is not, as noted previously, a general move- 

 ment of the flock in one direction; the flock as a whole is stationary. 



