TIME-ENERGY USE AND LIFE HISTORY STRATEGIES 



145 



Table 1. Nutritional value of foods eaten by birds. After data in Hunt (1972) and E. H. Dunn 



(1973). 



proportion of protein in relation to total bulk. 

 Protein is vital to growth of nestlings (Fisher 

 1972; Lemmetyinen 1972), and 4-8% protein 

 in the diet seems to be required for minimal 

 maintenance of adults (Martin 1968; Fisher 

 1972). Some sea birds (such as puffins, Prater- 

 cula) that eat a varied diet raise their young 

 exclusively on fish (Bedard 19696; Nettleship 

 1972; Sealy 1973a). 



Other aspects of nutrition, such as vitamins 

 and minerals, are also important to avian 

 health (Brisbin 1965; Fisher 1972). To further 

 complicate matters, nutritional values vary 

 with season, as do birds' requirements for 

 them (Myton and Ficken 1967; Moss 1972). 

 Adults must adjust their time and energy 

 allocation to foraging to optimize not only 

 energetic, but also nutritional return. 



Optimal time and energy allocation has 

 been studied in theory (Orians 1971; Schoener 

 1971; Pulliam 1974; Katz 1974) and some di- 

 rect observations have been carried out, 

 largely on seedeaters (Bookhout 1958; Myton 

 and Ficken 1967; Royama 1970; Moss 1972; 

 Willson 1971; Willson and Harmeson 1973). 

 The direct studies, in particular, point out the 

 basic importance of studying cost-benefit 

 ratios by interrelating complex factors of food 

 availability, searching patterns, and type, 

 size, and caloric and nutritional value of 

 foods. 



Time-energy Use Beyond 

 the Cost of Living 



This section concerns variation in time and 

 energy allocated by seabirds to activities 

 above and beyond the cost of living particu- 

 larly to migration, molt, and reproduction. 

 Allocation to such items as avoidance of pre- 

 dation and competition is not considered here, 

 because they are not readily analyzed as ac- 

 tivities to which time and energy are devoted 

 in a specific part of the annual cycle. 



The previous discussion dwelt on energy 

 considerations and could have referred to al- 

 most any group of birds. The following treat- 

 ment centers on time use of northern seabirds. 

 Little is known of energetics beyond the cost 

 of living, although estimates have been made 

 for certain aspects of migration, molt, and re- 

 production (Nisbet 1963; Hussell 1969; Hart 

 and Berger 1972; Payne 1972; Ricklefs 1974). 

 Essentially nothing is known, however, of the 

 relationship of such costs to the amount of 

 energy available to the bird once basic mainte- 

 nance costs have been met (productive 

 energy). Because such complete data are not 

 available, the following account dwells largely 

 on variation in timing and total time devoted 

 to activities beyond basic maintenance. 



