340 
clearly demonstrated (Fig. 15). It seems likely 
that breeding kittiwakes do not regularly fly 
out to sea as far as murres, but rather feed 
closer to shore. Regular patterns of movements 
which may exist are not evident from the data. 
Kittiwakes do not exhibit as distinct a pattern 
of daily activity fluctuations as do murres 
(Swartz, 1966), and do not characteristically 
fly as straight a course, so that possible flight 
trends might tend to be obscured. No move- 
ment, abundance, or distributional phenomena 
associated with daily rhythms are evident. 
One kittiwake in winter plumage was col- 
lected at about 70°50'N, 165°30'W near the 
edge of the polar ice pack. The reproductive 
tract was undeveloped and brood patches were 
not present. It is likely that many of the adult 
kittiwakes seen on the open ocean far from 
shore are nonbreeders. 
Sabine's Gull (Xema sabini) 
These birds were seen on six occasions and 
all but one were immatures (Fig. 10). The 
only adults (six birds) were seen at 70°46'N, 
165°42'W, near the northernmost point on 
the cruise track. No particular distributional 
pattern is evident. 
Arctic Tern (Sterna paradisaea) 
Arctic Terns were seen on 11 occasions in 
groups of from 1 to 17 birds, of which 7 were 
immature and the rest (43) were adults. Most 
of the sightings were within about 50 miles of 
a shoreline and all but 1 were within 40 miles 
of land (Fig. 10) . 
Murres (Uria lomvia and U. aalge) 
Thick-billed and Common Murres are very 
similar in appearance and could not be differ- 
entiated consistently under the conditions pre- 
vailing at sea. They are therefore considered 
together and such differences as exist between 
them are discussed at the appropriate places. 
The abundance and distribution of murres 
is plotted in Figures 16, 17, and 18. Due to 
the large total number of observations, only 
ten-minute count data are presented. Murres 
were the most abundant birds on the Chukchi 
Sea and were almost always visible from the 
ship even far from shore. Murres were seen 
in all but 24 (16%) of the 146 ten-minute 
PACIFIC SCIENCE, Vol. XXI, July 1967 
counts. Of these 24 negative counts 19 were 
made in an area near and within Kotzebue 
Sound in which very few birds of any kind 
were seen. 
Clear correlations between murre distribution 
and water temperature were found in this study. 
A striking decrease in the number of murres 
was noted on August 14 as the ship passed 
from colder waters to the warmer waters near 
Kotzebue Sound, crossing the 9°, 10°, 11°, 
and 12°C isotherms as plotted by Fleming 
et al. (I960: Fig. 5). (These isotherms repre- 
sent the temperature 5 meters below the sur- 
face.) R. H. Fleming (personal communica- 
tion) has observed this correlation on previous 
cruises in the area. Storer (1952:185) showed 
that the main breeding range of the Thick- 
billed Murre lies in areas where the August 
surface water temperatures are below 10°C 
and that the temperature tolerance of the Com- 
mon Murre tends to be somewhat higher. Storer 
(1952:187) cited Salomonsen’s (1944) claim 
that low temperatures retard spring molt and 
breeding in murres. This is clearly a local or 
individual response and would reinforce the 
contention that water temperatures could in 
part account for local distribution patterns. 
As the ship passed deeper into Kotzebue 
Sound on August 14 a subsequent sharp drop 
in water temperature occurred, but no increase 
in murres was evident except near Chamisso 
and Puffin islands, where small numbers of 
Common Murres were seen. Grinnell (1900:7) 
reported "immense numbers" of Thick-billed 
Murres breeding on these islands but did not 
report Common Murres. Neither species seems 
any longer to be an abundant breeder. 
The situation with regard to distribution 
and temperature is complex and at present re- 
mains unclear. Possibly not only water temper- 
ature but salinity, food supply, depth, and 
distance from breeding concentrations are 
interrelated factors. The speculation that a pro- 
gressive northern range extension of the Com- 
mon Murre is occurring which is correlated 
with long-term warming trends is provocative. 
Far too few data are available at present, how- 
ever, to consider the hypothesis in detail. 
In colder waters, murres were seen on all 
but 3% of the 10-minute counts. Even in these 
cases, murres were observed between the count- 
