VALUE OF BIRDS TO MAN. 



71 



trees near the shore of the Musketaquid a small flock of 

 Myrtle and Black-poll Warblers, busily feeding on a swarm 

 of plant lice. There were not more than fifteen birds. The 

 insects were mainly imagoes, and some of them were flying. 

 The birds were pursuing these through the air, but were also 

 seeking those that remained on the trunks and branches. I 

 watched these birds 

 for some time, noted 

 their activity 7 , and 

 then passed on, but 

 returned and ob- 

 served their move- 

 ments quite closely 

 at intervals all day. 

 Toward night some 

 of the insects had 

 scattered to neigh- 

 boring trees, and a 

 few of the birds 

 were pursuing them 

 there ; but most of 

 the latter remained 

 at or about the place 

 where the aphis 

 swarm was first seen, and they were still there at sundown. 

 The swarm decreased rapidly all day, until just before sunset 

 it was difficult to find even a few specimens of the insect. 

 The birds remained until it was nearly dark, for they were 

 still finding a few insects on the higher branches. The plant 

 lice I had secured for identification were destroyed or lib- 

 erated during the night, probably by a deer mouse which 

 frequented the camp ; so the next morning at sunrise I went 

 to the trees to look for more specimens. The birds, how- 

 ever, were there before me, and I was unable to find a single 

 aphis on the trees. The last bird to linger was more suc- 

 cessful than I, for it was still finding a few ; but it soon gave 

 up the effort, and left for more fruitful fields. Probably a 

 few insects escaped by flight ; but in examining the locality 

 in 1905 I could not find one. The apparently complete 



Fig. 29. Warblers destroying a swarm of plant lice. 



