6
Black Storm Petrel
(Oceanodroma melania)
Pronounced ship followers, these birds usually showed a gradual buildup
astern during the day. After a peak in the area just south of the mouth
of the Gulf of California, a broad gap of some 1200 miles passed with only
a single sighting. From Coast Rica to Panama, however, the birds were
again present in good numbers. While I see no mention in the literature,
this discontinuity suggests to me that when the breeding population returns
to the breeding grounds in northern Baja, a nonbreeding segment of the
population (immatures ?, first-year birds?) remains in the southern end
of the species range.
Least Storm Petrel
Halocyptena microsoma
One bird was tentatively recorded as this species on 2 June. Two "Dark-
rumped" Storm Petrels seen off Panama may have been this species as well.
Red-billed Tropicbird
Total Observations - 6
The six birds, scattered from the second to the twelfth day, indicate
the broad range and low relative numbers of this bird. Three birds were
seen in conjunction with the large Manx flocks on 5 June. Birds were
heard calling at sea.
Brown Booby
Total Observations - 118
The Brown was the first Booby to appear and high numbers were logged
when close to the coast on 4 and 5 June. Many immatures, 50-75 percent,
were seen in the Manx flocks, and others were found riding turtles. After
a 700-mile absence, browns were again common off Coast Rica and Panama
where proportionally more adults were observed.
Red-footed Booby
Red-feet were first logged on 7 June, but were probably present on
the sixth as well, off Acapulco. No birds were seen after the ninth when
a "great many" appeared. Most sightings were of non-adult birds. I did
not see any white adults to my knowledge.
Blue-faced Booby
Total Observations - 11
Blue-faced Booby showed the same type of occurrence as the Red-foot;
appearing and disappearing in the same three-day span. Most sightings
were of adults.
Frigatebird Species
Total Observations - 28
Only one bird was observed well enough to positively identify as a
Magnificent, however, all were presumed to be that species. The first
bird was sighted off northern Costa Rica. Twenty of the 28 birds were
seen in the Gulf of Panama.