Nelson and Hamer 



Chapters 



Nesting Biology and Behavior 



At a given nest, the two adults appear to have distinct 

 plumage colorations. A light brown and a dark chocolate 

 brown adult (sex of each unknown) have been observed 

 attending nests on 24-hour shifts, indicating possible sexual 

 plumage dichromatism (n = 8 nests) (Fortna, pers. comm.; P. 

 Jones, pers. comm.; Naslund 1993a; Nelson 1991,1992; 

 Ritchie, pers. comm.; Singer and others 1991). In addition, 

 the white patches on the nape of the neck and cheek have 

 varied between adults at a single nest, and individuals at 

 different nests (n = 7 nests) (Fortna, pers. comm.; Hamer and 

 Cummins 1991; P. Jones, pers. comm.; Nelson 1991, 1992; 

 Simons 1980). The variations in these nape and cheek patches 

 may provide a means for identifying individuals. 



Murrelets have been observed leaving their egg unattended 

 for 3-4 hours during the morning, mid-day, and evening (n = 

 4 nests; Naslund 1993a, pers. comm.; Nelson and Peck, in 

 press; Simons 1980). Seabirds often leave their eggs unattended 

 to maximize foraging time and accumulate sufficient energy 

 reserves for lengthy incubation shifts (Boersma and 

 Wheelwright 1979, Gaston and Powell 1989, Murray and 

 others 1983). Murray and others (1993) have hypothesized 

 that the benefits of increased foraging time during egg neglect 

 often outweigh the disadvantages of leaving the egg 

 unattended. Disadvantages of egg neglect include predation, 

 heat loss, and exposure to the elements. In Oregon, an egg 

 was believed to have been taken by a corvid when adults left 

 their nest unattended (Nelson and Hamer, this volume b). 



Timing of Incubation Exchanges 



Adults usually exchange incubation duties at dawn (n = 

 12 nests), although Simons (1980) believed exchanges may 

 have taken place at dusk at a ground nest in Alaska. Incubation 

 exchanges generally occur before official sunrise, and often 

 correspond with the first auditory detections of murrelets 

 each morning (Naslund 1993a; Nelson and Peck, in press; 



S.W. Singer, pers. comm.) (table 2). The timing of exchanges 

 were significantly affected by weather patterns and light 

 levels; birds arrived later during overcast or rainy conditions 

 (Naslund 1993a, pers. comm.; Nelson and Peck, in press). 

 In addition, birds arrived earlier in areas of higher latitude 

 likely because of longer periods of twilight. In Prince William 

 Sound, Alaska, incubation exchanges occurred from 37-82 

 minutes prior to official sunrise ( x = -52, s.e. = 3.1, n = 14 

 observations at 5 nests) (Naslund, pers. comm.). In Oregon 

 and California, the timing of incubation exchanges ranged 

 from 3 1 minutes before to 1 minute after official sunrise ( x 

 = -18.5, s.e. = 0.7, n = 85 observations at 7 nests) (Naslund 

 1993a; Nelson and Peck, in press; Singer and others 1991; 

 S.W. Singer, pers. comm.) (table 2). No nocturnal incubation 

 exchanges were observed during intensive observations in 

 California (Naslund 1993a, Singer and others 1991); nocturnal 

 surveys have not been conducted elsewhere. 



Incubating birds usually left immediately after the arrival 

 of their mate. Most incubation exchanges lasted 3 to 60 

 seconds ( x = 26.0 seconds, s.e. = 4.5, n = 76 observations at 

 7 nests), although at one nest in California one exchange 

 lasted 3 minutes and 40 seconds (Naslund 1993a; Nelson and 

 Peck, in press; S.W. Singer, pers. comm.) (table 3). The 

 arriving adult often remained motionless on the nest limb 

 before occupying the nest and commencement of incubation; 

 this waiting period lasted 14 to 357 seconds in California and 

 Oregon (Naslund 1993a; Nelson and Peck, in press). 



Egg-Hatching. Brooding Behavior, and 

 Chick Development 



The single murrelet chick hatches after 27 to 30 days of 

 incubation (Carter 1984; Hirsch and others 1981; Sealy 1974, 

 1975a; Simons 1980). Adults become active before the egg 

 hatches, standing and turning more frequently than earlier in 

 the incubation period (Naslund 1993a; Nelson and Peck, in 



Table 2 Mean time of incubation exchanges in relation to official sunrise at Marbled Murrelet nests by ante 1 



1 Data from Naslund. pers. comm.; Nelson and Peck, in press; S.W. Singer, pers. comm. 



2 Incubation exchanges were not observed in British Columbia and Washington. 



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



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