Time-Energy Use and Life History 

 Strategies of Northern Seabirds 



by 



Erica H. Dunn 



Long Point Bird Observatory 

 Point Rowan, Ontario, Canada 



Abstract 



Time and energy budgets can be compared among species of birds with very 

 different ecology as a way of summarizing differences and as an approach to 

 determining selective pressures on each species. This paper reviews time-energy 

 use of northern seabirds. Energetic cost of maintenance (basal metabolism, 

 thermoregulation, and procurement and processing of food) depends largely on 

 the following factors: (1) small birds have higher metabolic costs per unit size 

 than do larger ones; (2) body structure affects the cost of locomotion as well as of 

 food procurement; (3) climate affects metabolic costs; and (4) food availability 

 and nutrition vary among food types, and throughout the year within a food 

 type. Little is known of maintenance energetics in seabirds. Time and energy 

 allocations to items beyond basic maintenance are also compared. Patterns and 

 costs of molt and migration are known only in a general way, and the variety of 

 possible patterns suggests that more research would be of value. Almost nothing 

 is known of location and daily activities of seabirds outside the breeding season. 

 The review of breeding season activities is more comprehensive, and stresses the 

 variety of factors known to affect timing, and the total time devoted to and the 

 energetic costs of various aspects of reproduction. Some of these factors are 

 weather, year, geographic location, feeding conditions, age, sex, and distance of 

 food source from the breeding colony. Species characteristics such as clutch size, 

 egg and yolk size, developmental type, growth rate, food type, and behavior com- 

 bine with environmental variables to make seabirds a very diverse group in time 

 and energy budgeting. Time-energy studies and determination of productive 

 energy (energy remaining after maintenance needs have been met) can be useful 

 in pinpointing those groups of birds and the times of year when birds are most 

 vulnerable to environmental stress. Life history considerations suggest that 

 most seabirds are adapted to low population turnover and would not be able to 

 recover quickly from sudden increases in mortality. 



Effective management of a population re- phasize the wide variation of species ecology 



quires manipulation of the factors most criti- within this avian group. 



cal in causing population increase or decrease. Time and energy patterning is being used as 

 Deciding what these factors are and which are the basis of ecological comparison for the fol- 

 most suitable for effective manipulation is lowing reason. Any activity of an animal re- 

 very difficult due to the complexity of life quires time and energy use; therefore, the pat- 

 cycles and possible factors affecting demog- terning of use makes a common thread to 

 raphy. It takes a thorough knowledge of a which allocation to all activities in a bird's life 

 species and of its relationships with the biotic cycle can be related. Time-energy patterns can 

 and abiotic environment to make effective be compared among birds with diverse food 

 management decisions. The following review types, habitats, life cycles, and life expec- 

 of seabird time and energy use is meant to em- tancy, and therefore offer an opportunity for 



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