De Santo and Nelson 



Chapter 3 



Reproductive Ecology of Auks 



There is some indication that hatching success of the 

 Marbled Murrelet is low compared to other alcids (Nelson 

 and Hamer, this volume b). Combining observations 

 throughout the range of the Marbled Murrelet, 67 percent (n 

 = 20) of the eggs of 30 monitored nests successfully hatched. 

 Egg predation was documented or strongly suspected to be 

 the cause of failure for five of the 1 1 (45 percent) hatching 

 failures (Nelson and Hamer, this volume b). 



When the clutches of alcids are lost or fail to hatch, 

 some species (e.g., Razorbills, Common and Thick-billed 

 murres, Atlantic Puffins, and Black Guillemots [see Harris 

 and Birkhead 1985 for review], Pigeon Guillemots [Ainley 

 and others 1990b], Cassin's Auklets [Ainley and others 1990a; 

 Manuwal 1979], Horned Puffins [Wehle 1983]) lay 

 replacement eggs. Egg replacement in murres has been 

 reported to be between 15 and 43 percent (reviewed by 

 Boekelheide and others 1990; Byrd and others 1993). Ten 

 percent of Cassin's Auklet pairs replaced naturally lost eggs, 

 and 54 percent replaced eggs removed by researchers 

 (Manuwal 1979). Hatching and fledging success of 

 replacement clutches was often lower than first clutches 

 (Ainley and others 1990a; Byrd and others 1993; Manuwal 

 1979; Murphy 1994). The incidence of egg replacement is 

 low for Least and Crested auklets (Piatt and others 1990) 

 and Xantus' Murrelets (Murray and others 1983) and 

 apparently does not occur in Ancient Murrelets (Sealy 1976). 

 Cassin's Auklet is the only alcid known to lay a second 

 clutch following the rearing of their first brood (Ainley and 

 others 1990a; Manuwal 1979). Hatching and fledging success 

 of second clutches were usually lower than those of first 

 clutches (Ainley and others 1 990a). It is not known if Marbled 

 Murrelets lay replacement eggs or if they attempt to raise 

 more than one brood per season. 



Development and Survival of the Young 



Newly hatched alcids are downy (table 7) and are brooded 

 by their parents for 1 to 10 days (table 8) until homeothermy 

 has been achieved (table T). Body mass of hatchling alcids is 

 proportional to egg mass (fig. 4, r 2 = 0.98, P < 0.001) and 

 adult body mass (fig. 5, r 2 = 0.91, P < 0.001). Alcid chicks 

 are between 6 and 15 percent adult size at hatching (table 7). 

 Newly hatched Marbled Murrelet chicks at 15 percent adult 

 body mass, are large in comparison to the other alcid chicks 

 (tables 7-9). 



Most alcid chicks are semi-precocial (table 7). Parents 

 feed their semi-precocial young at the nest for 27-52 days 

 until they reach at least 60 percent adult mass. Kittlitz's 

 Murrelet may be an exception; the body mass of one fledgling 

 was reported to be 40 percent that of an adult (Day and 

 others 1983) (table 9). For most semi-precocial species, the 

 young reach independence at the time of fledging (table 8). 



The Synthliboramphus murrelets have precocial young. 

 For up to 2 days after hatching, precocial alcid chicks are 

 brooded but are not fed at the nest. Following this time, they 

 depart the nest at only 12-14 percent adult size and accompany 

 their parents to the sea where they receive additional care 

 until reaching independence at approximately 4 weeks of 

 age (tables 7, 8, and 9). 



Murres and Razorbills are intermediate to these two 

 patterns of development (Gaston 1985; table 7). Their 

 young leave the nest at about 20 days of age, earlier than 

 semi-precocial species, but much later than precocial species 

 (table 9). At fledging, murre and Razorbill chicks are 

 around 20 to 30 percent adult mass, lighter than semi- 

 precocial young, yet heavier than precocial young (table 

 9). The chicks accompany their male parents to the sea 



so 



at 60 



(0 



I 

 o> 



o 







X 



40- 



20- 



y = 1.44 + 0.68x R A 2 = 0.98 



40 80 



Egg mass (g) 



1 20 



Figure 4 Relationship between mean egg mass and mean hatchling 

 mass for 18 alcids (see tables 4 and 7 for values). 



80 



</> 60 



(0 



E 



05 



co 



40 



20- 



y = 11.42 + 6.67e-2x R A 2 = 0.91 



400 



800 



1 200 



Adult mass (g) 



Figure 5 Relationship between mean adult mass and mean hatchling 

 mass for 18 alcids (see tables 3 and 7 for values). 



42 



USDA Forest Service Gen. Tech. Rep. PSW-152. 1995. 



