62 



L. W. SOWL 



murre that was taken at Kodiak in 1867. 



The Gulf of Alaska is at the periphery of the 

 breeding range of the thick-billed murre. 

 While it probably occurs in mixed colonies 

 with the common murre throughout this area, 

 the thick-billed murre is much less abundant. 

 Occasionally in the Gulf of Alaska, a colony 

 will be occupied predominantly by the thick- 

 billed murre. Gabrielson and Lincoln (1959) 

 noted that the thick-billed murre outnum- 

 bered the common murre in many colonies in 

 the Aleutians and that it became progres- 

 sively more common at higher latitudes. 



We have almost no data relative to the 

 species composition of murre colonies in the 

 Gulf of Alaska. Until we do it will not be pos- 

 sible to fully understand the population 

 status of the thick-billed murre. It appears 

 that changes in the species composition of 

 murre colonies in the Bering Sea may be an in- 

 dicator of perturbation. The data for the Gulf 

 of Alaska are still too fragmentary to provide 

 any indication of whether or not the same in- 

 dicator would work there. Close monitoring of 

 the Shumagin Islands colonies over a number 

 of years might produce the answer. 



Earlier in this paper I noted the dramatic 

 changes in species composition of murre colo- 

 nies on Walrus Island. Gabrielson and Lincoln 

 (1959) also commented on this well-docu- 

 mented and anything but static situation. In- 

 vestigators who visited this island during 

 1976 reported seeing no murres on the island 

 and only small numbers on offshore rocks. 

 James Bartonek (personal communication) 

 said that this situation has prevailed for 

 several years. 



There is an indication that a similar popula- 

 tion fluctuation and change in species com- 

 position of murre colonies have also occurred 

 on St. Matthew Island. Bent (1963) found 

 mostly common murres and few thick-billed 

 murres at St. Matthew. Hanna (1916) saw 

 only thick-billed murres. Later, Gabrielson 

 (1941) found this to be true in 1940. 



Dramatic fluctuation in murre populations 

 may be common and, at least in some cases, 

 the two species may be affected differently. 

 Perhaps this phenomenon has potential for 

 providing us with an indicator of some natu- 

 ral perturbations. 



Peterson and Fisher (1955) expressed the 

 opinion that thick-billed murres arrived at the 



nesting ledges later than the common murre 

 and had to take the sites that were left. Tuck 

 (1960) reported data from the western Atlan- 

 tic showing that thick-billed murres arrive 

 later than common murres. On the other 

 hand, Belopol'skii (1961) reported data show- 

 ing that the two species arrive on breeding 

 colonies in East Murman simultaneously. At 

 Cape Thompson, Swartz (1966) found that 

 thick-billed murres arrived about a week be- 

 fore common murres. The date of arrival, 

 while perhaps a contributing factor, is prob- 

 ably not decisive. Interspecific competition of 

 another sort is indicated. 



In mixed murre colonies where there are 

 large numbers of common murres, this species 

 occupies the choice nesting sites. Thick-billed 

 murres are usually left with the narrower 

 ledges while the common murres occupy the 

 longer, broader ledges (Belopol'skii 1961). The 

 broader ledges have lower chick and egg mor- 

 tality (Spring 1971). Spring also noted that 

 thick-billed murres are excluded from the cen- 

 ters of mixed colonies. Johnson (1938) found 

 that this contributes to higher losses of eggs 

 to predators and to the loss of other social 

 benefits of occupying the colony center (John- 

 son 1941). 



Kozlova (1961) said that during the occupa- 

 tion of a colony there is a sharp competitive 

 struggle between the two species. In the end 

 thick-billed murres are pushed out to the pe- 

 riphery of the colonies or left with narrow 

 ledges or other equally unfavorable sites. 

 Spring (1971) studied the functional anatomy 

 of both species and concluded that the com- 

 mon murre is more successful in these encoun- 

 ters because it has a more upright gait and 

 greater agility than the thick-billed murre. 



It follows that in a portion of their respec- 

 tive ranges, where the two species overlap and 

 where there is an equal chance that either 

 common murres or thick-billed murres will 

 dominate a given colony, the common murre 

 dominates. I conclude from this that where 

 there are dramatic changes in species com- 

 position of murre colonies, such as at Walrus 

 Island, it is probably because the common 

 murre has been greatly reduced in numbers at 

 the colony. 



Spring (1971) concluded that the common 

 murre is well adapted to pursuit and capture 

 of pelagic fishes and that the thick-billed 



