De Santo and Nelson 



Chapter 3 



Reproductive Ecology of Auks 



returned to breed in the same burrow in consecutive years. 

 Two studies reported at least 70 percent of Black Guillemots 

 returned to use the same nest sites within the same nest 

 colonies year after year (Asbirk [1979] and Petersen [1981], 

 as cited by Harris and Birkhead 1985). Murray and others 

 ( 1983) observed that 64 percent of Xantus' Murrelets retained 

 the same nest sites for two years, and Roby and Brink (1986) 

 found that 91 percent of Least Auklets used the same nest 

 entrance in two consecutive years. 



At least six alcids show mate fidelity (table 2). Divorce 

 rates have been reported to be approximately 24 percent for 

 Crested Auklets (Jones 1993a) and approximately 7 percent 

 for Black Guillemots and Atlantic Puffins. These figures 

 were confirmed by Harris and Birkhead (1985). Emslie and 

 others (1992) have shown that mate retention has a positive 

 influence on reproduction of Cassin's Auklets; both fledging 

 and breeding success were higher for pairs that practiced 

 mate retention. 



No studies have been conducted on individually marked, 

 breeding Marbled Murrelets, but indirect evidence suggests 

 that they show both mate and breeding site fidelity. Murrelets 

 are primarily observed in groups of two throughout the year, 

 and many groups include a male and female (Carter 1984, 

 Sealy 1 975c). Strong and others ( 1 993) observed at-sea groups 

 of murrelets in spring and summer and reported that of 49 1 8 

 groups, 55 percent consisted of pairs. The possibility exists 

 that these twosomes were mated pairs, although without 

 observations of marked birds this is speculative. Marbled 

 Murrelet activity has been documented in the same forest 

 stands for periods up to 18 years (Divoky and Horton, this 

 volume), and murrelet nests have been found in the same 

 trees (Nelson and others 1994; Nelson and Peck, in press; 

 Singer and others, in press), and on the same general location 

 of tundra (Simons 1980), in consecutive years. These 

 observations suggest breeding site fidelity. Reuse of nests 

 has recently been documented for the ground nesting Kittlitz's 

 Murrelet, a close relative of the Marbled Murrelet (Naslund 

 and others 1994). 



Adult Life History Characteristics 



Historically, the Great Auk, which became extinct in 

 the 1 800s, was the largest member of the Alcidae, ca. 5 kg 

 (Harris and Birkhead 1985). At present, the murres are the 

 largest alcids (ca. 1 kg). Fifteen alcids are small by comparison, 

 having body masses less than half that of the murres (table 

 3). The Marbled Murrelet has a mass of 220 g, approximately 

 22 percent that of the murres. 



Adult annual survival has been estimated for ten species 

 (table 3). The lowest estimates of this population parameter 

 are 75 percent reported for both the Least Auklet, the smallest 

 alcid (ca. 85 g), and 77 percent for the Ancient Murrelet, a 

 relatively small alcid (ca. 200 g), (fig. 1, r 2 = 0.45, P < 0.05). 

 The larger alcids, Common and Thick-billed murres, 

 Razorbills, and Atlantic Puffins (ca. 1004, 941, 620, and 



100 



y = 79.76 + 1.28e-2x R2 = 0.45 



400 800 



Adult mass (g) 



1200 



Figure 1 Relationship between mean adult body mass and percent 

 annual adult survival for ten alcids (see table 3 for values). 



460 g, respectively), have higher survival estimates ranging 

 from 89 to 94 percent. 



Adult annual survival has not been measured for Marbled 

 Murrelets. However, based on the relationship between adult 

 body mass and annual survival (fig. 1), Marbled Murrelets 

 (ca. 220 g) are predicted to have an annual adult survival of 

 83 percent, comparable to alcids of similar size (i.e., the 

 Ancient Murrelet, ca. 206 g, 77 percent survival, or the 

 Crested Auklet, 272 g, 86 percent survival). 



Alcids are considered long-lived although this life history 

 aspect has not been well studied. Longevity of several 

 individuals of several species has been documented from 

 recovery of marked birds or their bands. Values range from 

 5 years for an Ancient Murrelet to 32 years for a Common 

 Murre (table 3). Values determined from band returns may 

 be indicative of band longevity, not bird longevity. These 

 values should, therefore, be considered minimums (see Clapp 

 and others 1982 for discussion). It is not known how long 

 Marbled Murrelets live; no reports of recovered banded 

 birds have been made. 



Alcids exhibit deferred maturity with most species 

 beginning to breed between 2 and 8 years of age (table 3). It 

 is not known at what age Marbled Murrelets begin to breed, 

 but an estimate of 2 to 4 years is reasonable based on 

 information available for other alcids. 



At least several alcid species breed annually once they 

 reach sexual maturity (table 3). For example, over 80 percent 

 of Least Auklets (Jones 1992) and 90 percent of Xantus' 

 Murrelets (Murray and others 1983) bred in consecutive 

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

 second clutch following the rearing of their first brood (Ainley 



36 



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



