142 



E. H. DUNN 



comparison not available through other kinds 

 of analysis (King 1974). 



The amounts of time and energy allocated 

 by an organism to different aspects of sur- 

 vival and reproduction should be regarded as 

 being molded by natural selection to optimize 

 (not necessarily to maximize) lifetime repro- 

 ductive output (Fisher 1958; Williams 1966; 

 Schoener 1971). Thus, differences in time and 

 energy use between species should reflect 

 adaptation to different biotic and abiotic envi- 

 ronments. By comparing time and energy use, 

 one can gain insight into the selective pres- 

 sures on each species and have a basis on 

 which to compare complex ecology more 

 meaningfully than if one listed other types of 

 differences. 



This review of time-energy use in northern 

 seabirds cannot be comprehensive, largely be- 

 cause many of the necessary data are lacking. 

 It stresses major areas of difference, however, 

 and points out aspects about which little is 

 yet known. 



Cost of Living 



Every animal must expend a basic amount 

 of energy on normal maintenance, excluding 

 activities normally allocated to a relatively 

 narrow time span, such as reproduction. This 

 "existence energy" expenditure consists of 

 basal metabolism, thermoregulation, and the 

 costs of gathering and processing food, and 

 could also be referred to as the animal's basic 

 "cost of living." In discussing the compo- 

 nents of the cost of living, energy use is em- 

 phasized and time largely ignored partly be- 

 cause metabolism occurs irrespective of time 

 (it is not something the animal can turn off for 

 a period) and partly because time use in nor- 

 mal maintenance and foraging has been little 

 studied. 



Metabolism 



Basal metabolic rate (BMR) depends 

 greatly on body size (Lasiewski and Dawson 

 1967; Zar 1968), and the costs per unit size are 

 higher for a small bird than for a large one 

 (Fig. 1). The BMR is somewhat lower in sea- 

 birds and other nonpasserines than in pas- 



METABOLIC 



O 



6 o 



POWER (WATTS) 



O! 



O 



in o 



01 

 o 



CO 



Fig. 1. Energy cost of various metabolic functions 

 in relation to body size in birds. "0 Existence" 

 refers to total metabolic costs of caged birds held 

 at 0C. From Calder (1974). 



serines of similar size (Dawson and Hudson 

 1970). 



The relationship between BMR and body 

 size is paralleled by that between size and 

 other metabolic costs, such as for thermo- 

 regulation at a given temperature and for ac- 

 tivity (Fig. 1; Kendeigh 1970; Tucker 1970; 

 Schmidt-Nielsen 1972; Berger and Hart 1974; 

 Calder 1974). Basal metabolic rate can there- 

 fore be used as an index of the overall cost of 

 living as far as metabolic functions are con- 

 cerned. Small birds must allocate a greater 

 proportion of their energy resources than 

 larger ones to merely staying alive, and have a 

 higher cost of living. 



The suggestion in Fig. 1 that it is easy to 

 measure activity costs in a straightforward 

 manner is misleading, because the figure rep- 

 resents measures taken under standard condi- 

 tions. Factors known to affect the cost of 

 flight, for example, include anatomical adap- 

 tations (such as wing loading and wing shape), 

 the type of flight (ascending, descending, glid- 



