alighted in a tree. Thirty yards, however, is a short flight even 
for a sparrow. But it is enough to show that flight, if not 
sustained flight, was possible after this mutilation. Not until 
more than one-third of the quills along the whole length of the 
wing were removed, did the flight become obviously laboured. 
And he found that what was true of the sparrow, was equally true 
of the wings of insects. 
Though these experiments demonstrate, in a very unmis- 
takable manner, that flight with a greatly reduced wing area is 
possible, we have no evidence that this reduction would make no 
difference to the length of time the bird could remain on the 
wing. And this is a very important matter. 
An aspect of flight which has now to be considered is that of 
birds which fly in troops. Some species always travel thus, 
others only on occasions. Rooks and gulls afford instances of 
this, when, during windy weather, or for other reasons, they 
congregate and fly round and round in great circles, at a con- 
siderable height. Small wading-birds, like ringed plovers and 
> The last named furnish a 
dunlin, commonly fly in “ bunches.’ 
singularly interesting sight when thus travelling; for their 
evolutions are so amazingly timed. As if at a given signal every 
bird in the troop will change its course at the same moment, and 
in the same direction, so that now one sees a flickering mesh-work 
of grey, and now a shimmering as of snow-flakes, as first the grey 
47 
