SEA ICE AS A FACTOR IN SEABIRD DISTRIBUTION 



11 



allows such species as the Lams gulls, which 

 typically roost on hard substrates, to occur in 

 large numbers well offshore. 



Sea Ice Reduces Wind Chill 



The unevenness of the upper surface of the 

 ice reduces the speed of winds directly over 

 the ice, thus providing a microhabitat and re- 

 ducing the amount of wind chill for birds sit- 

 ting on and next to the ice. 



Sea Ice Decreases Wave Action 



Ice floating on the water reduces the sur- 

 face disturbance of the water. Although 

 swells pass through areas with much ice 

 cover, waves do not. In addition, surface 

 waters on the lee side of ice floes and cakes 

 usually have little surface disturbance. Sur- 

 face feeders may be able to locate prey more 

 easily because of these reductions in surface 

 disturbance. 



Specific Effects of Ice 

 on Birds in the 

 Western Arctic 



The retreat of the pack ice each spring and 

 the formation of new ice each fall greatly af- 

 fect a large area of the Arctic Ocean off the 

 coast of Alaska and much of the Bering Sea. 

 Specific ways in which birds are affected by 

 ice in the western Arctic are discussed on a 

 seasonal basis. All observations are my own, 

 unless otherwise stated. 



Winter 



Chukchi and Beaufort Seas 



From late November to mid- April, ice cover 

 of the Chukchi and Beaufort seas is almost 

 complete. The only areas where birds can be 

 expected to winter in these seas are the 

 chronic lead systems. Such lead systems are 

 found off Wainwright and Point Barrow and 

 south of the Point Hope-Cape Thompson 

 area (Shapiro and Burns 1975). Only the black 

 guillemot (Cepphus grylle) is known to regu- 

 larly winter offshore from Wainwright and 

 Point Barrow (Gabrielson and Lincoln 1959; 

 Nelson 1969). In the Point Hope-Cape Thomp- 

 son area, glaucous gulls (Larus hyperboreus), 

 the common murre (Uria aalge), and the thick- 



billed murre (U. lomuia) occur throughout the 

 winter (Swartz 1967). It is likely that black 

 guillemots are also found in this area. 



The lack of chronic lead systems in the 

 Beaufort Sea precludes the presence of win- 

 tering seabirds. The one species that may be 

 found wintering in the Beaufort is the Ross' 

 gull (Rhodostethia rosea). Ross' gull is be- 

 lieved to winter primarily in the Arctic Ocean 

 (Bailey 1948). The number of sightings that 

 have been obtained in both the eastern and 

 western Arctic indicate that the species may 

 winter over much of the Arctic Ocean. It may 

 thus be expected to occur in both the Chukchi 

 and Beaufort seas during winter. 



Ice cover not prey abundance plays the 

 major role in severely limiting bird numbers 

 in the Arctic Ocean in winter. Prey is known 

 to be abundant in parts of the Arctic Ocean 

 during the period of ice cover. In the Chukchi 

 Sea, Eskimos fishing through the ice can 

 catch 23 kg of arctic cod per person per day 

 (D. C. Foote, unpublished data). Eskimos jig 

 for the fish at considerable depths, and the 

 cod do not appear to be as common directly 

 below the ice as they are in summer. The ef- 

 fects of new ice (which forms on the underside 

 of the ice during the winter) on the under-ice 

 fauna are not known. The abundance of am- 

 phipods in ice-covered waters in winter is 

 demonstrated by the experience of the 

 Greeley Expedition in the eastern arctic. They 

 discovered that any scrap of food thrown into 

 a lead was quickly consumed by amphipods. 

 Nets were made to catch the amphipods and 

 the availability of this food source played a 

 major part in the survival of the expedition 

 (Schmitt 1965). 



Aside from the food found in leads in the 

 ice, the only food available to birds in the 

 Beaufort and Chukchi seas in winter is carrion 

 and the feces of mammals found on the pack 

 ice. The presence of the arctic foxes on the 

 pack ice during the winter demonstrates the 

 availability of scavenging opportunities on 

 the ice. Arctic foxes on the pack ice live on 

 feces and the remains of seals killed by polar 

 bears (Urus maritimus). Polar bear and seals 

 are both common in the Beaufort and Chukchi 

 seas in winter, but no scavenging seabirds are 

 found there in the winter. It was thought that 

 the ivory gull (Pagaphila eburnea) was asso- 

 ciated with marine mammals during the win- 



