V ° 191^ X ] Tyler, Simultaneous Action. 199 



after time, apparently without cause, but of their accord, one can- 

 not help believing that some purpose, perhaps unknown to the birds 

 themselves, underlies these interruptions. But more mysterious 

 than the purpose of these sudden risings, is the means by which a 

 large number of Sparrows decide, with the unanimity of a single 

 bird, to fly up. 



One's first thought is that the birds in a flock start in response to a 

 note of warning given by one of their number. It is not necessary 

 to suppose a leader; any bird perceiving danger, or fancying that 

 he perceives it, might sound a warning which would arouse his 

 companions to retreat. That a man, even although he stands 

 very near a flock of birds, seldom, if ever, hears an alarm note, — - 

 or indeed any note at all, — is no proof of the absence of a signal. 

 However, one feels a little skeptical when he considers the almost 

 incredibly rapid response to a hypothetical signal inaudible to 

 human ears. I believe also that the Sparrows themselves give 

 more positive indication that in their concerted actions they do not, 

 or need not, depend on signals. It is a common habit of the 

 House Sparrow when gathered together, often in large companies, 

 to chatter or scold. Each bird repeats for minutes at a time bis 

 "chape" or "chillip" note, adding his voice to the din of the 

 chorus. These choruses often end on the instant. No orchestra 

 leader could more quickly silence the instruments under his control 

 on one beat, yet, in the case of the Sparrow, it is unbelievable that 

 an alarm note could be heard above the general uproar. 



There is another point which counts against the practicability of a 

 signal. It is chiefly when large numbers of Sparrows are assembled 

 in a flock that the sudden uprisings are conspicuous. One might 

 almost say that the unanimity was directly in proportion to the 

 number of birds present. That this proportion would appear 

 to hold is self evident, — for the larger the rising flock, the greater 

 the impression on the eye ; but a little observation will show that a 

 small flock of Sparrows acts in a very different way. A small 

 flock of House Sparrows will generally remain feeding in the street 

 until they are frightened away, and then they will leave the feeding 

 ground severally, a few birds at a time. Those nearest the ap- 

 proaching danger, or the most timid, start first, to be followed suc- 

 cessively by the remainder. Here are the very conditions under 



