9 
GUADALUPE ISLAND SURVEY 
The Guadalupe Island portion of the cruise was concerned primarily with 
pinnipeds. The work on 26, 27 April was not planned but was substituted 
for pelagic work due to rough weather at sea. 
The r/v Ellen B. Scripps provided logistic support for the Guadalupe 
Island survey work on May 1-4. Landings were made on the island from an 
outboard-powered skiff capably handled by Ron McConnaughey, Chief Tech¬ 
nician on the Cruise. Many of the landings were made against rocks which 
would certainly have torn the skiff apart had it not been expertly handled. 
A rubber assault raft would be very satisfactory for these landings. 
Black-vented Shearwater Puffinus puffinus opisthomelas 
Estimated nesting pairs: 100 _ 20$ 
This bird is breeding on Islote Negro, although the' islet is small and the 
habitat not ideal for procellarid nesting. The soil is volcanic material, 
primarily scoria. Much of this material is loosely consolidated, making 
digging difficult. This species is a burrow nester. The burrows have nar¬ 
row entrances (4 to 7 inches) and are generally shallow but long. Burrows 
were found up to 18 inches deep that then went four feet parallel to the 
surface. The egg is deposited at the extreme end of the burrow. 
Most of the birds were on eggs during our visit. Of 4-3 burrows ex¬ 
amined 70$ of the birds were on fresh eggs. One bird was found on a pipped 
egg and a few moderately incubated eggs were found. 
On this visit 23 birds were banded. Dr. Hubbs has banded this species 
on Islote Negro since 1963. In this time either one or two hundred birds 
have been banded, and six returns have been taken. Thus there is to date a 
3 percent return rate on these bandings. As suggested by Dr. Hubbs, 
(Appendix II) "this strongly indicates the integrity of the breeding popula¬ 
tion." However, one evening off the south end of the island, a feeding 
flock of about 2500 Black-vented Shearwaters was encountered. A concentra¬ 
tion such as this off a breeding island suggests that the birds may be 
island based. However, to our knowledge the birds breed only on Islote 
Negro. I recall seeing a specimen in the San Diego County Museum taken in 
breeding condition and possibly from a burrow from the outer islet off the 
south end of Guadalupe. This is a second possible current breeding area, 
but would these two small islets support the large number of feeding birds 
observed off the island? Dr. Hubbs suggest that these are nonbreeding 
birds from Isla Natividad, the main breeding island for this species, 
located 180 miles southeast of Guadalupe off Point Eugenia, Baja California. 
The possibility exists that there are many more birds based on these two 
small islands than we expect. All previous work has been done during the 
day and, as is the case with most procellarids, nocturnal populations are 
much higher than are diurnal ones. A small amount of night work during the 
breeding season will resolve this question. 
4 
