FAUNA OF THE ALEUTIAN ISLANDS AND ALASKA PENINSULA 185 



Figure 33. — Pallas's thick-billed murres. 



ditioned to the fear stimulus, either by human disturbance or by 

 excessive predation, progressive reduction of the colony may 

 result. 



In the Aleutian district, no such drastic reduction of a popu- 

 lation came to our notice. Probably there is a minimum of 

 human intrusion. Furthermore, in many cases the historical 

 background was unknown. 



The murre is one of the animal species preyed upon rather 

 extensively by raptorial forms. Yet, it does not find it necessary 

 to produce more than a single young in a season. On the other 

 hand, it nests in close-packed colonies and exists in large num- 

 bers, and it seems that local predation has little effect. 



In common with some other sea birds, murres often succumb 

 to the elements and are found washed upon the beach. 



Beals and Longworth, reporting for Unimak Island in 1941, 

 wrote : 



Between April 2 and 4 numerous dead and sick murres were along all the 

 beaches. We counted 37 dead birds along 3 miles of beach. The condition 

 was general along the strait [probably Isanotski strait], we were told. Old- 

 timers on Unimak told us that this happens every spring and that some 

 years the beach is black with dead birds. Swimming in close to the waterline 

 many of them appeared to be sick or very weak and hardly able to dive in 

 shallow water. Altogether we saw 38 dead birds and 40 or more very weak 

 ones along 3 miles of beach. For three days before this heavy winds and 

 snow blew from the southeast. 



