200 
THE CONDOR 
Vol. XIII 
Imagine the same numbers passing across a line a number of miles long, or 
better, across the breadth of Siskiyou County, and for say eight hours a day for sev- 
eral days; the numbers become incredible. 
The butterflies were all migrating southward. In the early morning none were 
to be seen, but by half past nine they were in full migration. During the night 
they rested among the leaves on the trees or shrubs, on the sides of buildings or in 
any other convenient place. 
With the life cycle taking but a year, it at first seems hard to explain why 
the numbers should be so much greater one year than another. One factor govern- 
ing the phenomenon is the presence or absence of fortunate conditions for hiberna- 
Fig. 70. BUTTERFLIES GATHERED TO DRINK AT A DAMP PLACE IN THE 
ROAD. PHOTOGRAPH TAKEN AT SISSON, SISKIYOU COUNTY, CALIFORNIA, 
AUGUST 23, 1911. 
tion of the butterfly. As the pupae are parasitized to a large extent, in the 
neighborhood of 35 percent, and doubtless the larvae are also parasitized, the 
abundance or scarcity of these parasites must govern the numbers to some extent. 
A third factor, and without doubt an important one, is the part played by birds in 
the destruction of larva, pupa, and imago. Many of the pupae, 15 percent or 
thereabouts, apparently showed the wmrk of birds, and as will be showui birds have 
an important part to play in the destruction of the butterflies. To what extent birds 
feed on the larvae is not known. Probably not to as great a degree as on the pupa 
and imago forms, for the larvae are w'ell protected by stiff hairs. The scarcity or 
