Burket: 



Chapter 22 

 Table 6 Mean food values of selected invertebrates and fishes' 



Food Habits and Prey Ecology 



Prey 



Mixed species 



/Loligoidae and Ornroastrephidae ' 



Shrimp 



Mixed species 



(Penaeidae and Pandalidae) 

 Pacific Hening 



. upea harengus paUaa) 

 European Anchovy 



(Engraulis encrasicholus) 



Food Energy 



Protein 



Total Lipids [fat] 



kcal 



92 



15.58 



138 



106 



20.31 



1.73 



Mixed species 



( Sebasies spp. ! 



' Amounts in 100-g raw samples, edible portion (Exler 1987) 



eels (<10 cm) which have low body weights and high water 

 content seemed, on purely energetic grounds, to be low- 

 quality food. Because many different seabird species use 

 sand lance in their diet, it may be that the overall abundance 

 and availability of these fish compensates for the low energy 

 value. Sand lance may also contain essential nutrients which 

 seabirds have a need for, and the higher water content may 

 also be important physiologically. The estimation of total 

 energy content is complicated by dehydration of fish 

 specimens: thus. Montevecchi and Piatt in Hislop and others 

 ( 1 99 1 ) urged seabird biologists to compare dry weight energy 

 densities across studies. Both sets of researchers also noted 

 the value of including wet calorific values as well. 



The work of Hislop and others (1991) provides data for 

 comparison of energy values between sand eel and herring 

 which indicates that herring have much higher total energy 

 value than sand eel (table 7). Unfortunately, there is no data 

 available for both herring and sand eel of murrelet nestling 

 prey size (60. 1-120.0 mm) in July or August to allow a more 

 relevant comparison. 



Roby (1991) studied the diet and postnatal energetics in 

 three species of plankton-feeding seabirds. Lipid-rich diets 

 were associated with shorter brooding periods, higher rates 

 of nestling fat deposition, and larger lipid reserves at fledging. 

 The energy cost of growth was a relatively minor component 

 of nestling energy budgets; most assimilated energy was 

 allocated toward maintenance and fat deposition. Once growth 

 requirements for protein had been met, any additional 

 assimilated protein was metabolized to meet maintenance 



costs, and the energy saved was stored as fat. High lipid diets 

 were associated with higher rates of lipid deposition by chicks, 

 but not higher growth rates. Instead, constraints operating at 

 the level of tissues are apparently responsible for most of the 

 variation in growth rate among seabirds. Large lipid reserves 

 at fledging presumably enhance post-fledging survival. 



Discussion 



Conservation and recovery of the murrelet will depend 

 in part on a better understanding of the interaction between 

 the factors affecting the species inland and at sea. The 

 studies described in this chapter have shed some light on 

 this relationship and have indicated the need for 

 comprehensive management of marine resources and inland 

 nesting habitat. 



There is a need for additional study of murrelet diet, 

 especially in the southern end of its range. Winter diet 

 studies are also needed to help understand why some murrelet 

 populations disperse to other locales during the non-breeding 

 season. Comparison of prey abundance and composition 

 between breeding and non-breeding foraging areas may help 

 explain these movements. 



Additionally, more research on the use of inland lakes 

 and estuaries as foraging sites is needed, across all seasons. 

 This aspect of the murrelet' s life history has not received 

 adequate attention except by Carter and Sealy (1986) and 

 Hobson (1990). Though there are few large inland lakes in 

 the coastal area of Washington, Oregon, and California, 



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



243 



