Gulls in Central Pacific — Sibley and McFarlane 
317 
TABLE 2 
Biweekly Gull Populations on Kure Atoll 
During the Winter of 1964-1965 
DATE 
GULLS SIGHTED 
MINIMUM 
NO. OF 
NEW GULLS 
Nov. 
1-15 
1 Larus argentatus 
collected 
No other gulls seen 
1 
Nov. 16-30 
None 
Dec. 
1-15 
None 
Dec. 
16-31 
6 L. glaucescens seen, 
1 collected, 2 
banded 
3 Rissa tridactyla seen, 
1 collected 
9 
Jan. 
1-15 
7 L. glaucescens seen, 
none with bands 
2 L. hyperhoreus seen 
6 
Jan. 
16-31 
4 L. glaucescens seen 
2 L. hyperhoreus seen, 
1 collected 
0 
Feb. 
1-15 
1 L. glaucescens 
collected 
2 gulls seen, 1 carcass 
found 
0 
Feb. 
16-28 
1 L. glaucescens seen 
2 L. hyperhoreus seen 
1 
Mar. 
1-15 
3 L. glaucescens 
collected 
1 L. argentatus 
collected 
1 L. schistisagus 
collected 
No other gulls seen 
4 
Mar. 
16-31 
None 
Apr. 
1-15 
1 L. argentatus 
collected 
No gulls seen after 
April 1 
1 
The Galapagos Islands, with two breeding 
species, would appear to be the only true oceanic 
islands in the tropical latitudes that boast breed- 
ing colonies of gulls. The westward extension 
of the cool Peru current, however, exerts con- 
siderable influence on the marine fauna of these 
islands and they cannot be considered eco- 
logically typical of the tropics. Our field in- 
vestigations reveal that gulls frequently reach 
islands of the central Pacific during the winter. 
In some years one or more species is present in 
considerable numbers. The lack of breeding 
gulls in these islands cannot therefore be at- 
tributed to lack of potential colonizers. 
Gull distribution in the central Pacific is pre- 
sented, by species, in Table 3. Analysis of their 
normal breeding and wintering ranges reveals 
no particular pattern of dispersal. All Herring 
Gulls collected from the Leeward Hawaiian 
Islands have proven to be Larus argentatus 
vegae. This subspecies breeds only in Siberia 
and winters along the Asian coast of the Pacific, 
occasionally occurring on the American coast as 
far south as British Columbia. L. schistisagus 
occurs along the western Pacific shores from the 
Gulf of Anadyr to China and Formosa. Speci- 
mens of Rissa tridactyla , L. glaucescens, L. 
Philadelphia, and L. hyperhoreus could con- 
ceivably have originated from the North Amer- 
ican coast. L. delaivarensis and L. californicus 
breed in the plains of western North America 
and winter along the Pacific coast as far north 
as Washington and British Columbia. L. pipix- 
can breeds in the northern interior of North 
America. L. atricilla has the easternmost affinity, 
breeding on the Atlantic coast from Nova Scotia 
to Venezuela, the Gulf of Mexico, and southern 
California and Mexico on the Pacific coast, with 
some birds wintering on the Pacific coast from 
Mexico to South America. 
The wide range in their probable origins and 
irregular appearance in the Hawaiian Islands 
suggests that wind drifting may be primarily 
responsible for their appearance. 
Bryan (1964), Frings (1965^, 1965^), and 
Amadon (1965) have recently commented on 
possible factors restricting gull distribution. 
Frings presented several theories concerning the 
failure of gulls to colonize the Hawaiian Islands. 
These theories center on two main themes. The 
first is essentially non-adaptability to local food 
sources. He notes that gulls are essentially 
scavengers and depend on a rich source of dead 
or easily obtained food. Productivity of tropical 
waters is notoriously low and the molluscs and 
other invertebrates which are so abundant on 
the rocky beaches of the higher latitudes are 
almost totally absent. The second theme, and 
that which Frings believes most important, in- 
volves the functioning of the nasal glands and 
their role in salt excretion. He postulates that 
gulls must have access to fresh or brackish water 
