10 
Leach Storm Petrel Oceanodroma leucorhoa 
On 27 April we found only one large immature with down on the belly. 
This bird represents the last of the winter breeding race which has been 
called 0. 1. kaedingi . Later in the summer, a race thought to be 0. 1. 
soccoroensis breeds on the island. This temporal separation of the" two 
races was first described by Hubbs (Systematic Ecology 9 (3 & 4) 134-147, 
i 960 .) However, the subspecies 0. 1. kaedingi is not accepted by some tax¬ 
onomists as a distinct race from soccoroensis . But the fact remains that 
there are at least two populations, if not races, breeding here in the 
same environment at different seasons. 
During our visit to Islote Negro a Burrowing Owl ( Speotyte comicularia ) 
was flushed from the rocks and was seen flying around the island several 
times. Where the bird was originally sitting we found remains of several 
Oceanodroma . And as the survey continued many other Oceanodroma remains 
were found. The owl has done considerable damage to breeding storm petrels. 
One downy young was found partly eaten in the back end of a burrow. Did the 
owl go into that burrow and kill and eat the storm petrel there, leaving the 
remains? We found no indication of the owl having preyed on any of the 
other breeding birds. 
Cassin T s Auklet Ptychoramphus aleutica Estimated nesting pairs: 200 t 
This little alcid is a burrow-nester on Islote Negro. They reportedly 
dig their own burrows. On Islote Negro the burrows were seldom more than 
six inches deep, but were up to four feet in length. In some areas the 
burrows are found among burrows of Black-vented Shearwaters and Xantus 
Murrelets. Fresh eggs, pipped eggs, and one large immature with traces of 
down were found. 
We were using number three bands on these birds. The bands fit well 
on some birds, but on others they were too large and slipped off the tarsus. 
Was this tarsus size variance due to sex, age, or were we handling two dif¬ 
ferent races of birds? There is a second subspecies, P. a. australis van 
Rossem, described from the San Benito and San Roque islands. 
Xantus Murrelet Endomychura hypoleuca Estimated nesting pairs: 150 1 
This attractive small alcid was nesting on Islote Negro. It nests in 
burrows and cavities in the rocks. Nests were found with one, two, and 
three eggs, but two seems to be the normal clutch size. There is consider¬ 
able color variation in eggs from the same clutch. One clutch was found 
with one buffy egg and one olive-brown egg. There were also a few burrows 
that contained adults tending small downy young. Fifteen Xantus Murrelets 
were banded with Dr. Hubhs 1 bands on Islote Negro on 27 April. 
On nights of 30 April, 2 and 3 May, Xantus Murrelets flew aboard the 
R/V Ellen B. Scripps . On these three nights 6 l birds were banded, 25 of 
these with POBSP bands. Fifty-nine were banded aboard ship while anchored 
in Melpomine Cove, next to Outer Island where the birds breed, and two were 
banded in Northeast Bay. A breakdown of these birds follows: 
t 
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