King, provides data on the distribution of the northern, predominantly white-breasted and southern, dark-breasted morphs of this species. Data were collected systematically from the north-central, south-central and eastern Pacific during all months of the year. In spring and summer, when most species of this area breed, high densities of seabirds are found in the sea near the islands.
In winter, the width of the currents decreases and the surface current is weaker. Ashmole and Ashmole (1967) present an excellent review of the general biology of birds and their food organisms in the equatorial current system. Most of the islands in this area are found within 100 miles of the coast, but a few are oceanic.
All specimens are in the collection of the National Museum of Natural History, Smithsonian Institution, Washington, D.C. The following POBSP personnel and collaborators contributed observations during the course of the Program: Kenneth E.
Patrick J. Gould
Only the years and 1966 were included because of the patchy coverage in the North and Central Pacific in other years. NORTH-CENTRAL PACIFIC.—Sterns are present in the north-central Pacific throughout the year. Repeated observations northeast of the Hawaiian Islands illustrate seasonal expansion and contraction of the soot's distribution limits in the north-central Pacific (Figure 6).
At the end of the breeding season, adults and juveniles disperse widely across the sea, and many disappear from the North and Central Pacific. The Philippine Sea must therefore represent at least part of the sooty tern's non-breeding range in the North and Central Pacific. Other authors, including King and Pyle (1957) and Morzer Bruyns (1965), have shown some of the effects of ocean currents in the central Pacific on the density and distribution of seabirds.
Sooty terns were abundant at all times of the year in and around the Phoenix Islands. In the eastern Pacific it breeds only on San Benedikto Island of the Revilla Gigedo group. In the eastern Pacific Wedge-tailed Shearwaters have never been identified with certainty south of the Gulf of Guayaquil (latitude 3°S) (Le've'que, 1964b:53-54).
In the central Pacific, marine distribution and abundance were clearly linked to the birds' breeding cycles in the Hawaiian Islands and Johnston Atoll.
Gerald A. Sanger
Birds were present at low to moderate densities (x = 11-20 birds/observation, from a stationary vessel) in August in an area off the southern California Channel Islands, resulting in the highest abundance of the year. During June–September 1937 and 1938, Black-footed Albatrosses were concentrated in a cold spit off the California Channel Islands (Miller, 1940). They were present on 94 percent of the 88 days they spent in the area and accounted for 53 percent of all birds observed.
The peak of abundance occurred in August 1965 when albatrosses were 2.5 times as abundant as in the previous August. Because of the ship-following habits of the Black-footed Albatross and a resulting disparity in field recording techniques for this species, it was impossible to estimate actual abundance in the standard units of birds per linear mile of travel. January distribution (Figure 66): The densest concentration of birds occurred in the central Pacific over a broad front at ca.
February distribution (Figure 67): In the central Pacific, birds were seen in sufficient numbers as far as 11°N, 151°W, although notably lacking by several degrees of longitude in either direction. Concentrations were still found in the front at 25°N; no observations were made in the Leewards. Scattered birds were seen between northern Washington and 53 °N in the Gulf of Alaska; these views apparently represent the northernmost winter records for the species.
No black-footed albatrosses were seen south of 31°N in the area off California; a few birds were encountered within 25 miles of the coast. May Distribution (Figure 70): The most obvious feature of the May distribution in the central Pacific was the continued northward retreat of the population to 20°N. June Distribution (Figure 71): A continued northward retreat of the central Pacific population was evident this month; the southern limits were at 21°N, 160°W, although two widely scattered individuals were seen at 16°N latitude.
August distribution (Figure 73): In the central Pacific, Blackfoot was found even further north than during the previous months. Overall abundance from Washington and Oregon declined markedly beginning in August, and Diomedea nigripes numbers were erratically distributed in the region outside of southern California. December distribution (Figure 77): The population level in the central Pacific increased to an observed all-time high this month.
BLACK
CALCOFI
FOOTED ALBATROSS DATA
There also appears to be a tendency for high densities to occur further south in this band than in the other two. These high densities occurred rather irregularly and without the obvious evidence of the cycles shown in the other two bands. The bottom graph in Figure 63 shows that the highest number of birds usually occurred in the afternoon (1600) but never in the morning (0800).
First, there is a large latitudinal population shift that coincides with the breeding season, ie. the birds are in the southern part of their pelagic range in winter (breeding season), and in the northern part of their range in summer (Figure 64). Furthermore, a general scarcity of Blackfeet has been noted in the western Pacific at various seasons (Starrett and Dixon, 1946; Aronoff, 1960). This would explain, at least in part, the sharp reduction in the number of Blackfeet from Washington and Oregon between August and October.
Woodward (POBSP) shows a dramatic decline in the number of non-breeding Blackfoot during March and April on Kure Atoll. Overall movements, as indicated earlier in the literature review, show that some birds are in the area of the Aleutians as early as May (Gabrielson and Lincoln) and as late as November (Kenyon, 1950). This is common in the Bering Sea as a whole. - lake, considerably north of the great northern currents, the West Wind Drift and the Alaskan Current.
Thompson (1951) found that blacklegs tended to be more abundant in the California Current off California than in the eastern North Pacific Central Water. In the western Pacific, Kuroda (1955) saw his highest numbers of Diomedea nigripes in coastal waters off Honshu, roughly west of the Kuroshio-Oyashio convergence, in June and July. A detailed analysis of the relationship of albatross abundance and water temperatures in the CalCOFI area is beyond the scope of this paper.
Thus, if the blackfoot is indeed actively associating within a surface water temperature range of 14° to 22°C, one would expect most of the population to be found in the eastern North Pacific. AIR TEMPERATURE.-Air temperatures are closely correlated with ambient ocean surface water temperatures. It generally agrees with the findings reported here that the black-footed albatross is primarily an eastern North Pacific species, but with a proportion of the population in the western part.
Laysan Albatross [Diomedea immutabilis)*
Two were taken south of the western Aleutians, and the third was taken to the central Pacific. January distribution (Fig. 81): In the central Pacific, only scattered individuals were observed southwest of the main Hawaiian Islands to 17°15'N. June distribution (Figure 86): Laysans were common at relatively low densities (less than 3.2 BPS) in the Leeward, but were not observed in the rest of the central Pacific.
As spring approaches, they move north and by May can be found in the northernmost part of the Gulf. Two main trends similar to these are evident in the gross Laysan distribution. AIR TEMPERATURE.—The boundaries of the Laysan area appear to be parallel to the isotherms of about 5°.
At least 15 species and a variable number of subspecies (depending on the reviewer) are found in the areas of the Pacific Ocean covered in the present work. General collection was even more fruitful here than in the central Pacific, since certain forms, such as the two races of the Gala-. PELAGIC DISTRIBUTION.—The named race of Leach's Petrel is distributed in its tersea range over a large part of the Pacific with a definite center of abundance in the central Pacific.
As discussed in the breeding biology section, 90 percent of the birds breeding on Islote Negro in June 1968 had pure dark rumps. Suffice it to say that the field workers could not distinguish any differences in the calls of the two populations. Specimens of young kaedingi in the San Diego Museum of Natural History indicate the extent of the breeding season.
In the central Pacific, birds were commonly recorded south and southwest of the Hawaiian Islands up to 4°S, with one sighting south of 8°S. The petrel is one of the few white-rumped species in the Pacific that can be identified with a fair degree of certainty under most field conditions. Insufficient POBSP winter surveys in the Leewards, plus the very secretive nature of this storm in breeding areas, make it difficult to get a clear picture of the breeding cycle.
Aside from concentrations in the Gulf of Panama, most POBSP observations of the lesser Storm Petrel were along the coast of Baja California and mainland Mexico (Figure 117). Equally large concentrations recorded in the eastern Pacific west of the Galapagos Islands are of unknown origin, but most likely from breeding stations in the Marquesas Islands and Christmas Island.
