154 



E. H. DUNN 



100 



o 

 o> 



10 



10 



100 1000 



ASYMPTOTIC WEIGHT- GRAMS 



Fig. 10. Growth rate as a function of body weight. Growth rate T 10-90 represents the number of days to 

 grow from 10% to 90% of asymptotic weight (Ricklefs 1968). Data from Ricklefs (1968, 1973), E. H. 

 Dunn (1973), and Sealy (19736). Solid circles and regression line, altricial birds; solid triangles, semipre- 

 cocial birds except for seabirds with one-egg clutches; open circles, precocial shorebirds; open triangles, 

 precocial ducks, rails, and gallinaceous birds; solid squares, alcids with one-egg clutches; and open 

 squares, northern petrels, gannet, and Manx shearwater (Puffinus puffinus). 



at rates normal for semiprecocial chicks 

 (Fig. 10). Very slow growth may be related to 

 food stress (Lack 1968; Ricklefs 1968) or to re- 

 duction of reproductive effort in the adults 

 (discussed later). Contrary to Cody (1973), 

 slow growth in alcids does not correlate to the 

 distance adults must commute for food. (Cody 

 tried to directly compare growth in birds of 

 different sizes.) Chicks in nocturnal species, 

 however, tend to have slow growth rates 

 (Sealy 19736). 



Daily time budgets of adults raising nest- 

 lings also vary widely, depending on the 

 amount of brooding required, food require- 

 ments of the young, and foraging costs (which 

 differ in the breeding season from those at 

 other times of the year). 



Nestlings have imperfect control of body 

 temperature at hatching (Fig. 11) and develop 

 this capacity only gradually. Altricial birds 

 are hatched at a particularly undeveloped 

 stage; e.g., double-crested cormorants attain 

 reasonable control of body temperature in 

 moderate ambient temperatures only after 

 about 14 days (Fig. 11; Table 5). Semipre- 



cocial seabirds, which are more fully de- 

 veloped physically at hatching, attain control 

 of body temperature much sooner, in a matter 

 of several days, and precocial eiders can ther- 

 moregulate within a few hours after hatching 

 (Table 5). 



Until the age of temperature control, nest- 

 lings must be brooded almost constantly, and 

 occasional brooding takes place for some time 

 afterward, especially in severe weather, in all 

 species studied (Tinbergen 1960; Belopol'skii 

 1961; Weaver 1970; Dunn 1976a, 19766). 

 Thermoregulatory capabilities in cold 

 weather are better in ducklings of species 

 nesting at high latitudes than at lower ones 

 (Koskimies and Lahti 1964), and the same 

 may be true of gull species (Dawson et al. 

 1972). The cooling mechanisms of double- 

 crested cormorants are better than in the 

 more northerly distributed pelagic cormorant, 

 Phalacrocorax pelagicus (Lasiewski and 

 Snyder 1969). Thus, variation in cost of ther- 

 moregulation due to different environments 

 may be reduced through adaptation. 



Food requirements of the chick depend on 



