30 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4TH Ser. 
migration is studied on the ocean, the cause of these diamet- 
rically opposite conclusions is apparent, for upon the ocean the 
veil is removed and birds are seen in the act of migrating.’ 
Extensive migratory movements of old and young birds occur 
in broad daylight at a slight elevation above the surface of the 
water. Young birds, weak of wing, drop out of such move- 
ments in the exodus-migration, and are often the first birds 
seen by the observer stationed on or near the land, the offshore 
flights wholly escaping notice. It is held, therefore, that the 
preponderance of young-of-the-year, early or late in the exo- 
dus-migration, merely evidences that they have stopped by the 
way, and will later join experienced travelers and resume the 
journey.” 
Guidance by Physical Phenomena.—The series of observa- 
tions made by myself on the ocean in the vicinity of Point 
Pinos, California, demonstrate that the shearwaters passing 
that headland in the return-migration are guided in their 
course by the landmarks.* Repeated observations showed that 
the low fogs deflected their migratory movements toward the 
land, and when the land as well as the sea was hidden by the 
fog the migratory hosts became bewildered and lost their way, 
and when the fog lifted and the landmarks became visible 
again they immediately resumed their journey, manifesting that 
they were not endowed with a mysterious sense of direction, 
but were dependent upon physical phenomena for guidance.‘ 
The last link in the chain of evidence proving guidance by 
physical phenomena will be forged when return-migration to 
breeding stations on islands remote from continents has been 
studied by a trained student of migration. In the meantime 
there is no valid justification for lapsing into superstition 
under the guise of science. We know that the oceans have 
areas of abundant food where birds are numerous and areas 
CS Os Ee At A INO Ca 
+See my migration papers in Proc. Calif. Acad. Sci.; cf. Clarke, Studies in Bird 
Migration, v. 2, pp. 6, 11-15; Patten, Zoologist, 1913, pp. 189, 190. 
_ 7*It should be borne in mind that the latitudinal limit of the range of a species 
is not necessarily the longitudinal limit of its fly-line, and that the mere presence 
of the young near the upper limit of the breeding range is far from being conclusive 
proof that the young were reared in the locality. 
® Consult my detailed account, Proc. Calif. Acad. Sci., 3d ser., Zool., v. 2, par- 
ticularly pp. 281, 284, 285, 307-309. 
*In the vicinage of Point Pinos, breeding cormorants, fishing offshore, had no 
difficulty in finding their way through the fog back to their rookeries, nor did my 
boatman experience any difficulty in finding his way through the fog from the ocean 
to Monterey; both had kept their bearings. The shearwaters migrating down the 
coast, however, had no opportunity of determining their position by local landmarks, 
and in consequence lost their way. In this connection, see Cooke, Bull. No. 185, 
U. S. Dept. Agric., pp. 27-29. 
