One feeding eagle invariably attracts a crowd, below. 

 Displays, fights, and piracy ensue as the birds vie for salmon. 

 The Steller's eagle, with its deep, massive beak, opposite page, 

 is the only species of eagle on Kuril Lake able to penetrate the 

 thick skin ofsockeyes with relative ease. 



a challenge. Cashing in on another eagle's 

 work is quicker and easier than ripping 

 open a fresh carcass and is even worth the 

 energy lost in displaying and squabbling. 

 Subadults, which are not yet adept at ma- 

 nipulating salmon, must either steal part of 

 another bird's fish or resort to eating soft, 

 rotting carcasses. 



The dynamics of the Steller's eagles' 

 strategy are not those of classic piracy, in 

 which an entire prey is appropriated. 

 Rather, piracy and scavenging are com- 

 bined. Because a typical salmon provides 

 more than enough food to satiate a single 

 eagle, intruding birds do not so much steal 

 as use the valuable, surplus salmon. Group 

 feeding may be beneficial to the species 

 because large, unwieldy windfalls of food 

 are ultimately shared by many eagles. 



I was surprised to find that conflicts 

 reached their peak in frequency and inten- 

 sity when food was most abundant. Con- 

 flicts between two individuals were rare, 

 but when group size increased to five, the 

 number of conflicts rose exponentially. A 



major factor affecting the makeup of feed- 

 ing groups is the age of its members. Adult 

 eagles more often attacked feeding birds 

 and were more successful at piracy than 

 subadults. 



As has been suggested for herons, 

 storks, and gulls, the color of plumage 

 may play a role in the formation of 

 Steller's eagles' feeding groups. Subadults 

 must wait five full years before they attain 

 fully mature plumage, with the striking 

 white head, tail, and shoulders. Younger 

 birds are dark brown with a few white 

 spots, and their beaks are pale, lacking the 

 bright orange of their elders'. The contrast 

 between white and deep brown in the 

 adults makes them easy to spot at a feed- 

 ing site and, I believe, gives other eagles a 

 powerful visual signal of a particular 

 bird's place in the feeding hierarchy — in 

 which adults take precedence. I think this 

 holds true not just on the wintering 

 grounds but also on the breeding grounds, 

 where Steller's eagles tend to nest near 

 one another along salmon rivers and 



where several nesting pairs may share a 

 common hunting area. 



According to my best estimates, each 

 Steller's eagle consumes about fifty fish a 

 season at Kuril Lake. In oflier parts of the 

 Kronotskiy Reserve where no spawning 

 grounds exist, eagles may die in winter. 

 But on Kuril Lake they tend to gain 

 weight. I was even able to catch some by 

 hand on fire ground because, after gorging 

 on several pounds of salmon, the eagles 

 were unable to fly away. Of tiie seven win- 

 ters I have spent on the lake, flie one ex- 

 ceptional season was the winter of 1992- 

 93. During weather that was unusually 

 harsh, even for Kamchatka, ice covered 

 tire spawning grounds, making fish inac- 

 cessible to the eagles and aU the other 

 birds that rely on salmon for their winter 

 livelihood. Far fewer eagles congregated 

 on the lake. Perhaps the next couple of 

 winters will reveal whether this is a short- 

 lived phenomenon or a climatic trend with 

 greater, and grimmer, implications for the 

 wildlife of the area. 



As the spawning season winds down 

 and March approaches, most adult salmon 

 have reproduced and died. Food now be- 

 comes scarce. During this time, the com- 

 munal roost of the Steller's sea eagles, 

 which is located in stands of birch trees 

 some three to six miles from the lake, be- 

 comes particularly important as an area 

 where eagles exchange information re- 

 garding the location of food. When one 

 scouting eagle finds a spot with a few 

 salmon left, its soaring confreres wiU read- 

 ily find and join it. Eagles flapping in a 

 particular direction will soon catch the at- 

 tention of the birds still in the roost, and 

 the "word" will spread. This continues 

 until the lack of salmon and the hint of 

 spring send the eagles north to nest again. 



In the middle of March, when the ea- 

 gles begin to return to the northern coasts, 

 I too leave Kuril Lake. I board an orange 

 polar helicopter and rise above the deep, 

 bright water. From the air I can see the sin- 

 gle river that connects the lake to the sea, 

 the one artery that brings life to Kuril Lake 

 in the form of millions of spawning 

 salmon. D 



32 Natural History 2/94 



