TIME-ENERGY USE AND LIFE HISTORY STRATEGIES 



143 



160 



o 120 



80 



40 



LEVEL FLIGHT 



OS 10 15 20 25 30 



FLIGHT SPEED - MILES PER HOUR 



Fig. 2. Energy cost of flying at different speeds and 

 angles as compared with basal metabolic rate 

 (BMR). Solid lines and solid circle refer to flight 

 cost and BMR for budgerigar (Melopsitticus 

 undulatus}. Dashed line and open circle refer to 

 flight cost and BMR of the laughing gull. From 

 Tucker (1969). 



ing), and the speed of flight (Fig. 2; Tucker 

 1969, 1974; Hainsworth and Wolf 1975). The 

 cost of a series of short flights may be higher 

 than that for a long one because of the extra 

 energy required for takeoff and landing. A few 

 estimates have been made for the cost of 

 flight, mostly in birds moving almost con- 

 stantly (Lasiewski 1963; Nisbet 1963; Tucker 

 1972, 1974; Utter and LeFebvre 1970; Berger 

 and Hart 1974), but the methods may be in- 

 adequate for birds that fly short distances 

 frequently. 



Little work has been done on the cost of 

 locomotion in seabirds: that of Eliassen (1963) 

 on great black-backed gulls (Lams marinus), 

 Berger et al. (1970) on ring-billed gulls 

 (L. delawarensis), and Tucker (1972) on the 

 laughing gull (L. atricilla), and indirect cal- 

 culations of soaring flight characteristics in 

 albatrosses, Diomedea spp. (Cone 1964), and 

 the fulmar, Fulmarus glacialis (Pennycuick 

 1960). Swimming has been shown to be more 

 costly than flying in ducks (Schmidt-Nielsen 

 1972) and may be for seabirds as well. More 

 energy is also probably used in underwater 

 swimming than in flying. 



The energetic costs of thermoregulation 

 under natural conditions are not easy to esti- 

 mate. Thermal energy is gained from and lost 

 to the environment, and the degree of ex- 

 change depends not only on air temperature 

 but also on metabolic rate, insulation, body 

 temperature, posture, humidity, convection, 

 and radiation. Radiation, in turn, depends on 

 cloud cover, shade, and reflective and absorp- 

 tive characteristics of the organism and of the 

 environment (Porter and Gates 1969; Calder 

 and King 1974). Most of these quantities are 

 changing constantly, and insulation and 

 metabolic rate may vary on a seasonal basis 

 with acclimation (Dawson and Hudson 1970). 



At present, no direct measurement tech- 

 nique exists for determining natural thermo- 

 regulatory costs, although a few estimates 

 have been made (King 1974), including several 

 for seabird nestlings (Dunn 1976a, 19766 for 

 double-crested cormorants, Phalacrocorax 

 auritus, and for herring gulls, LOTUS argenta- 

 tus). For most birds, the temperature environ- 

 ment actually faced over a year's time has 

 never been measured, and for no bird has a 

 full description of the complete thermal envi- 

 ronment been made. It is clear that climate 

 and degree of exposure are important ele- 

 ments in the basic cost of living, and that 

 thermoregulatory costs average higher in 

 small birds than in larger ones, but beyond 

 that little information is available. Work on 

 thermoregulatory costs of free-living chicks of 

 two species of seabirds suggests that insula- 

 tive properties can lead to marked differences 

 in the metabolic costs of different species in 

 an essentially identical environment (Dunn 

 1976a, 19766). 



Food Procurement and Processing 



Gathering and processing food is another 

 major component of the cost of living. Both 

 the nutritional value of food and its avail- 

 ability (a rather vague term covering both 

 abundance and ease of capture) are extremely 

 diverse and variable, making estimations of 

 foraging cost and benefit difficult (Ashmole 

 1971; Fisher 1972; Sealy 1975a). 



Availability of food varies throughout the 

 year, particularly in marine invertebrates 

 that form the diet of many seabirds (e.g., 

 Spaans 1971; Bedard 1969a). High arctic 



