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, and 
then passed on, but \ Laos 
returned and ob- wey CS ae: 
4 
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 ’ ss 
were pursuing them apmeargt 
there; but most of 
the latter remained 
at or about the place ae 
where the aphis Fig. 29.— Warblers destroying a swarm of plant lice. 
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 
a 
as ae { 
wad 
x thet “ate \ aoe wis 
