Mar., 1915 
NOTES ON MURRELETS AND PETRELS 
77 
breeding ground on the islands. Just why the Socorro Petrel should he forced 
out by the above mentioned vermin (if such be the case), while the Black 
Petrel persists in abundance, is a question which for the present must remain 
unanswered. 
Black Petrels nest on all of the group with the exception of South Island 
and in aggregate numbers probably exceed the Socorros, though their habit 
of nesting in isolated pairs or at best small scattered colonies renders them 
much more difficult to obtain. Another factor which adds to the difficulty of 
collecting them is that very frequently the nesting site is under some great 
boulder or in a narrow, inaccessible crevice in a rock wall. T am morally cer- 
tain that, on these islands at least, although the Black Petrels occasionally do 
use burrows, these are not excavated by the birds themselves, but are merely 
abandoned ones of Socorro Petrel or Cassin Anklet. The normal site is a nat- 
Pig. 28. Adult and young Petrels: Oceanoclroma socorroensis 
at left; 0. melania at right. The larger size of the 
BILL OF THE LATTER IS EVIDENT, EVEN IN THE YOUNG 
ural one, such as a cranny in a rocky wall, beneath misplaced slabs of rock, in 
dark caves, or even under heavy bushes, sharing this last situation with 
socorroensis, birds of each species sometimes being found within a few inches 
of each other. 
The young of these two petrels are very similar in appearance. When 
first hatched the bills, tarsi and feet are a dirty pinkish, gradually darkening 
as the birds grow older till by the time they are the age of those figured (about 
two weeks) the parts mentioned are the solid, shiny black of the adults. Even 
in newly hatched chicks the difference in hills is plainly visible (see fig. 28), 
and no difficulty should be experienced in distinguishing the young even in 
the field should a young Black Petrel he taken from a Socorro burrow. The 
natal down is at first a light smoky gray, changing as the bird develops to 
