Burkett 



Chapter 22 



Food Habits and Prey Ecology 



Table 4 Size of prey items for adult and subadult Marbled Murrelets 



Range or size class 



LoKgp opalt 

 Unidentified mysids 



Thysanoessa inermis 



mmm 



Thysanofssa sap. 



Euphausia pacifica 

 Clupea harengus 



Engraulis mordai 



Cymatogasier aggregata 



0.1-30.0 

 30.1-60.0 

 60.1-90.0 



Carter (1984); length for invertebrates is total length, and fork length for fish 

 b Sealy (1975c); length same as Carter (1984) except as noted far Loligo opalescens 

 c Sanger (1987); length for all specimens is total length 



As noted by Carter (1984) and Mahon and others (1992), 

 murrelet nestlings are fed much larger fish than the adults 

 consume. Most nestling prey items were >60.1 mm, and 

 sand lance prey were >90. 1 mm (table 5). 



Schweiger and Hourston in Carter (1984) concluded 

 that second-year herring fed to nestlings were much less 

 abundant than the juvenile herring that adult murrelets ate 

 for themselves. Second-year sand lance and anchovy were 

 also not considered very abundant in Carter's (1984) study 

 area, which suggested that murrelets selected larger prey to 

 carry to nestlings, even though such fish were less abundant. 

 This behavior is consistent with optimal foraging theory 

 (Carter and Sealy 1990). and other seabirds have exhibited 



this same adaptive trait (Gaston and Nettleship; and Slater 

 and Slater in Carter 1984). 



The lengths of nestling prey probably represent second- 

 year fish (Hart in Carter 1984), thus, murrelet adults, subadults. 

 and hatching-year birds feed primarily on larval and juvenile 

 fish, whereas nestlings are most commonly fed second-year 

 fish. Therefore, both of these cohorts of the principal prey 

 species should be monitored and managed to assure maximum 

 productivity of murrelets in any one year. 



Energetics and Energy Values of Some Prey Items 



Energy values of prey items also help explain why 

 murrelets select certain prey species for themselves and their 



USDA Forest Service Gen. Tech. Rep. PSW-152. 1995. 



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