Nelson and Hamer 



Chapter 5 



Nesting Biology and Behavior 



Table 1 Marbled Murrelet tree and ground nests by state or province, site, year, and number of days of observation 



dances, birds frequently give soft, synchronous nasal 

 vocalizations. Pairs also chase one another in flights just 

 above the water surface throughout the spring and summer, 

 in what may be courtship behavior (see below about similar 

 behaviors exhibited at inland nesting sites). 



Copulation has rarely been observed. It is known to 

 occur within trees (n = 1 observation in Alaska; Kuletz, pers. 

 comm.) and on the water where it has been observed at least 

 15 times (Kuletz, pers. comm.; Naslund, pers. comm; Nelson, 

 unpubl. data; Van Vliet, pers. comm.). Preceding and 

 following copulation, the birds often vocalize with an 

 emphatic, nasal "eeh-eeh" call (Van Vliet, pers. comm.). We 

 expect that copulation primarily occurs at the nest based on 

 observations from other alcids (Sealy 1975a). 



Before they lay eggs, pairs probably visit the breeding 

 grounds, not only to pair and copulate, but also to select nest 

 sites. In Oregon, a pair was observed landing on a nest platform 

 for 3 mornings in early May, two weeks prior to laying an egg 

 at that site. Pre-laying visitation to nests, three to four weeks 

 before egg-laying, has been observed in other alcids (Gaston 

 1992; Nettleship and Birkhead 1985). 



Egg-Laying and Incubation Behavior 



Marbled Murrelets start to lay eggs as early as March 

 (Hamer and Nelson, this volume a). They lay a single egg 



weighing approximately 36-41 g (16-18.5 percent of adult 

 weight) (Hirsch and others 1981;Sealy 1975a; Simons 1980). 

 The egg is subelliptical in shape, and measures an average of 

 59.5 x 37.4 mm (n = 1 1 eggs) and 0.21 mm in thickness (Day 

 and others 1983; Hirsch and others 1981; Kiff 1981; Sealy 

 1975a; Simons 1980). The egg has a pale-olive green to 

 greenish-yellow background color, and is covered with 

 irregular brown, black, and purple spots which are more 

 prevalent at the larger end of the egg (Becking 1991 ; Binford 

 and others 1975; Day and others 1983; Kiff 1981; Nelson 

 1991, 1993; Nelson, and Hardin 1993a; Reed and Wood 

 1991; Singer and others 1991). 



After the female lays an egg, the pair begins 24-hour 

 shifts of incubation duty; one adult broods the egg while the 

 other forages at sea (n = 12 nests) (Naslund 1993a, pers. 

 comm.; Nelson and Peck, in press; Simons 1980; Singer and 

 others 1991). The incubating adults sit on the egg in a 

 flattened posture and remain motionless on the nest more 

 than 90 percent of the time (n = 4 nests) (Naslund 1993a; 

 Nelson and Peck, in press; Simons 1980). Other behaviors 

 observed during incubation at most nests include turning the 

 egg, re-arranging nest material, and preening. At nests in 

 California (n = 1) and Alaska (n = 5), the average occurrence 

 of these behaviors were 11, 8, and 1 time(s) per day, 

 respectively (Naslund 1993a, pers. comm.). 



58 



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



