De Santo and Nelson 



Chapter 3 



Reproductive Ecology of Auks 



and others 1990a; Manuwal 1979). Within and between year 

 breeding frequencies for Marbled Murrelets are unknown. 



The Egg and Incubation 



Most alcids, including Marbled Murrelets, lay a clutch 

 consisting of one egg (table 4). The guillemots and the 

 Synthliboramphus murrelets typically have clutch sizes 

 of two. 



Alcid eggs range in size from less than 20 g to over 100 

 g (table 4) and vary in proportion to adult mass (fig. 2, r 2 = 

 0.92, P < 0.001 ). Alcid egg masses typically represent between 

 10 and 23 percent of the laying female's body mass (table 4) 

 with the precocial species laying the heaviest eggs relative 

 to adult body size. Marbled Murrelet eggs (ca. 35 g) at 18 

 percent of adult body mass are also large. 



The duties of incubation are shared by both members of 

 the breeding pair (table 5). Incubation shifts can be as short 

 as several hours (e.g., Pigeon and Black guillemots) or as 

 lengthy as several days (e.g., Xantus', Ancient, and Japanese 

 murrelets) (table 5). Incubation is completed within 27 and 

 45 days (table 5). Overall, there is no significant correlation 

 between incubation period and egg mass (fig. 3, i 2 = 0.10, P 

 = 0.21). The eggs of four of the larger alcids (Rhinoceros 

 Auklet and Tufted, Horned, and Atlantic puffins), however, 

 require up to 45 days of incubation, while the small eggs of 

 the Least Auklet are incubated for a much shorter period of 

 time (ca. 30 days). 



Nine species of alcids are known to leave their eggs 

 unattended for periods of 1 to 19 days, particularly during the 

 early stages of incubation (table 5). Egg neglect is common in 

 Xantus' (Murray and others 1983) and Ancient murrelets 

 (Gaston and Powell 1989) occurring at nearly half of the nests 

 studied. Egg neglect can lengthen the period from laying to 



hatching (Gaston and Powell 1989; Murray and others 1983; 

 Sealy 1984), but can decrease the total number of days of 

 actual incubation necessary (see Murray and others 1983). 



Compared to other alcids, Marbled Murrelets have a 

 short incubation period (ca. 27-30 days) (table 5). Parents 

 exchange incubation duties every 24 hours (table 5), typically 

 during pre-dawn hours (Naslund 1993a, Nelson and Hamer, 

 this volume a; Nelson and Peck, in press; Simons 1980). 

 Simons (1980) noted a one-day period of egg neglect early 

 in incubation at an exposed ground nest of a Marbled Murrelet. 

 Additionally, at three tree nests, eggs were left unattended 

 for up to 4 hours during the day and evening (Naslund 

 1993a; Nelson and Hamer, this volume a; Nelson and Peck, 

 in press). It is not known if egg neglect occurs commonly at 

 Marbled Murrelet nests, but other alcid species which lay 

 their eggs in open nests (e.g., Common and Thick-billed 

 murres; see Gaston and Nettleship 1981) do not frequently 

 leave their nests unattended. 



Average hatching success exceeds 70 percent for over 

 half of the 19 alcids for which this parameter has been 

 measured (table 6). The lowest value (33 percent) was reported 

 for Xantus' Murrelets nesting on islands with high rates of 

 mouse predation (Murray and others 1983). Avian and 

 mammalian predation have been cited as a cause for clutch 

 loss in other studies as well (Birkhead and Nettleship 1981; 

 Drent and others 1964; Emms and Verbeek 1989; Evans 

 1981; Ewins and others 1993; Gilchrist 1994; Harfenist 

 1994; Jones 1992; Piatt and others 1990; Sealy 1982; 

 Thorensen 1964; Vermeer and Lemon 1986). Additional 

 causes of hatching failure include infertility and embryo 

 death (Evans 1981; Knudtson and Byrd 1982; Thorensen 

 1964), mechanical destruction of eggs or nests (Birkhead 

 and Nettleship 1981; Thorensen 1964), and adverse weather 

 (reviewed by Harris and Birkhead 1985). 



120 



3 



(0 80 



in 



a 



01 

 o> 



UJ 



40- 



y = 15.51 + 9.42c-2x R*2 = 0.92 



400 800 



Adult mass (g) 



1 200 



Figure 2 Relationship between mean adult body mass and mean egg 

 mass for 21 alcids (see tables 3 and 4 for values). 



50 



OT 



> 



a 



o 



5 40 



i 

 a. 



c 

 o 



(0 



3 

 O 



30- 



20 



y = 31.16 + 6.09e-2x R A 2 = 0.10 



40 80 



Egg mass (g) 



1 20 



Figure 3 Relationship between mean egg mass and incubation 

 period for 19 alcids (see tables 4 and 5 for values). 



38 



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



