BIOLOGY AND CONSERVATION OF THE COMMON MURRE 17 



Diet 



Diet information for common murres has been 

 obtained mainly from examination of stomach contents 

 from birds collected at sea (see summaries in Ainley 

 and Sanger 1979; Bradstreet and Brown 1985; Sanger 

 1987; Vermeer et al. 1987). Even though fish are the 

 primary prey of common murre adults and chicks, adults 

 can feed on other types of prey with different caloric 

 values that are less suitable for carrying to and feeding 

 chicks (e.g., euphausiids). Adults can eat larger fish (less 

 than 20 cm long) than are fed to chicks with fish size 

 limited by fish body depth (less than 40 mm; Swennen 

 and Duiven 1977). Adult diet tends to be more diverse 

 than chick diet in the breeding and nonbreeding seasons 

 and. in addition to fish and squid, can include molluscs, 

 polychaetes. and fish eggs. Diet composition varies 

 considerably between geographic areas and times of 

 year, including the proportion of fish and crustaceans 

 in the diet. Overall, much less information is available 

 on winter diet than summer diet. Various factors can 

 affect prey abundance, availability, and location on 

 short- and long-time scales (e.g., Ainley et al. 1993, 

 1994; Veil et al. 1997). 



In Oregon, northern anchovy (Engraulis mordax) 

 and rockfish (Sebastes spp.) dominated the diet 



throughout the year in 3 years studied, but murres 

 consumed more euphausiids and mysids (up to about 

 27% of the diet by volume) in July-August (Wiens and 

 Scott 1975; Scott 1973, 1990). Matthews (1983) also 

 found a diverse diet in Oregon that varied between years, 

 seasonally, and among individuals foraging in the same 

 area. Individual murres consumed up to seven different 

 taxa during a single foraging session. The most common 

 prey items included anchovies, juvenile rockfish. Pacific 

 tomcod (Microgadus proximus), whitebait smelt 

 (Allosmerus elongatus). Pacific herring (Clupea 

 harengus). Pacific sand lance (Ammodytes hexapterus). 

 speckled sanddab (Citharichthys stigmaeus), market 

 squid (Loligo opalescens), crab megalops (Cancer spp.), 

 and euphausiids. 



Murre diet was found to vary seasonally (i.e., 

 prebreeding, breeding, and winter), spatially (i.e., 

 coastal, mid-shelf, and outer-shelf waters), and between 

 years in coastal waters near murre colonies in central 

 California (Ainley et al. 19%; Figure 1.7). Diet was 

 most variable during winter and in El Nino periods. 

 During the prebreeding season (March-April), diet was 

 dominated by euphausiids (e.g.. Euphausia pacifica 

 and Thysanoessa spinifera) and juvenile rockfish in 

 outer-shelf habitats. Pacific whiting (also known as 

 Pacific hake; Merluccius productus) and rockfish were 



Figure 1.7. Variation in diet composition of 

 the common murre between three marine 

 habitats and three times of year in the Gulf of 

 the Farallones in central California, 1 985-1 988 

 (adapted from Ainley et al. 1996). Diet 

 categories are presented as percent of total 

 index of relative abundance (after Sanger 1 987). 

 Diet categories are coded: EU. euphausiids; 

 SQ. market squid (Loligo opalescens). NA, 

 northern anchovy (Engraulis mordax): PW. 

 Pacific whiting (Merluccius productus]: RK. 

 rockfish (Sebastes spp.); and OT. other. 



Coast 



Marine Habitats 



Mid-Shelf 



Ouer-Shelf 



Pre- 



Breeding 

 (Mar-Apr) 



5 Breeding 

 (May-Aug) 



Winter (Sep 

 Feb) 



m-7 



