ANIMAL BEHAVIOR, WITH EXAMPLES 247 



ordinary knot protruding slightly from the horizontal limb 

 of an oak tree. It would have been passed by without another 

 thought had not the knot suddenly evolved wings and taken 

 a zig-zag flight through the open woods. The cause of my aston- 

 ishment was soon explained when I saw it was a night hawk, 

 for this bird rests with its body parallel to the top of the limb, 

 unlike other birds. Moreover, his color matched the bark so 

 well that it was next to impossible to distinguish him from 

 some excrescence on the tree. 



On the last day of August, lOO^, at about five o'clock p.m., 

 I noticed a flight of night hawks going south. From the porch 

 of our home in Chicago I watched their flight as they came 

 scattered along restlessly pursuing their way. The open view 

 from where I stood would allow a vision of about a one-mile 

 stretch, looking east. At 5.26 p.m. I took note with watch 

 in hand and counted all the individual twilight birds that passed 

 the line of vision. In four minutes one hundred had passed the 

 line, the time then being five-thirty. In another three and a 

 half minutes one hundred more passed; the time now being 

 five thirty-three and a half. Still continuing counting, another 

 hundred birds passed just at 5.37h p.m., or in four minutes. 

 If this was a fair computation, one thousand five hundred 

 birds would pass in an hour. Allowing only six miles as 

 the width of the city, nine thousand birds would pass 

 over the line drawn across the city at a given point in 

 an hour. As a matter of fact, the birds fly in scattered flocks 

 over a large area, and while these flocks come periodically, 

 lasting into the night, there are quiescent spells when almost 

 no birds are seen in the sky for a space of a minute to several 

 minutes at a time. A fair estimate would indicate that eighteen 

 thousand birds pass over the city in a single night in this 

 migration the last of August. The birds seemed much more 

 plentiful fifteen years ago, when similar timing gave a larger 

 percentage during these migrations. 



The night hawk may be readily distinguished from its allied 

 neighbor, the whip-poor-will, while on the wing, by the presence 

 of a white spot conspicuously displayed on each wing. I 

 remember one spring finding the nest of the whip-poor-will 

 on the leaf -covered ground in a wet woods near Grand Crossing, 



