Nelson and Hamer 



Chapter 5 



Nesting Biology and Behavior 



Calls and fly-bys that indicate the impending arrival of 

 an adult may also be given at nest sites. On several occasions 

 in Oregon and Washington, incubating adults or chicks became 

 alert, and chicks gave begging calls, moments before the 

 arrival of the (other) adult (Hamer and Cummins 1991; 

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

 and Reimchen (1990) also mentioned keer and groan 

 vocalizations given by adults prior to incubation exchanges. 



Wingbeats have been heard during landings and take- 

 offs from nest branches at all nests, and while murrelets were 

 flying through the tree canopy. Murrelets appear to be able to 

 purposely create the wing sounds, because they are not heard 

 during all landings, take-offs, and flights through the canopy. 



Discussion 



Marbled Murrelet breeding biology, morphology, and 

 behavior, like that of other alcids, is affected by distance of 

 nest sites from food sources, risk of predation, and other 

 physical and biological factors (Cody 1973; De Santo and 

 Nelson, this volume; Vermeer and others 1987a; Ydenberg 

 1989). The risk of predation may be the most significant 

 factor in the development of alcid behavior, especially for 

 Marbled Murrelets in their forest nesting environment. 



Exposure to predation has influenced the length of 

 incubation shifts, chick feeding frequency, and fledging 

 strategy of alcids (Ydenberg 1989). Predator avoidance may 

 be the driving force behind the long incubation shifts of both 

 the Marbled (24 hours) and the Ancient (48 to 120 hours) 

 Murrelets (Synthliboramphus antiquus)(Gaston 1992), as 

 frequent visits to a nest can increase the chances of being 

 discovered by predators and endanger the parents and young. 

 Because of this risk, some species of alcids only feed their 

 chick once in a 24-hour period (nocturnal alcids with semi- 

 precocial young), whereas others (Synthliboramphus spp.) 

 produce precocial chicks that are not fed at the nest site. In 

 addition, feeding frequency within a species can vary among 

 nesting colonies, with young in safe sites receiving more 

 food than those in unsafe sites (Ydenberg 1989). Young that 

 receive multiple daily feedings grow faster and fledge earlier 

 than those with lower provisioning rates (Gaston and 

 Nettleship 1981). Early fledging helps to minimize nest 

 mortality (Cody 1971). 



Marbled Murrelets have optimized their survival 

 strategies by laying a single egg, feeding their chick relatively 

 frequently, and concentrating most of their activity in the 

 low light levels of dawn and dusk. With multiple daily 

 feedings, murrelet chicks grow relatively rapidly and 

 generally fledge earlier compared with most semi-precocial 

 alcids (De Santo and Nelson, this volume). Despite this 

 earlier fledging, Marbled Murrelet chicks are vulnerable in 

 their open nest sites for 27 to 40 days. Therefore, selection 

 of safe nest sites (Hamer and Nelson, this volume b) and 

 secretive behaviors to avoid predation are also necessary for 

 their survival. 



In response to pressures from predation at nesting sites, 

 alcids have developed specific behavioral characteristics (flight 

 behavior, nocturnal activity) and have selected nest sites in 

 inaccessible areas (burrows and crevices). Whereas most 

 alcids are diurnal, nine species, including Marbled Murrelets, 

 are primarily nocturnal or crepuscular (Synthliboramphus 

 murrelets, Cassin's [Ptychoramphus aleuticus] and Rhinoceros 

 [Cerorhinca monocerata] Auklets, Kittlitz's Murrelet, Dovekie 

 [Alle alle]). Activity during low light levels (or twilight 

 hours in the high arctic) minimizes predation by diurnal 

 avian predators like gulls and corvids (Ainley and Boekelheide 

 1990; Gaston 1992; Nettleship and Birkhead 1985). Most 

 alcids nest in inaccessible areas (burrows, crevices) to hide 

 from predators, however, some species nest in the open on 

 rock ledges (Common Murre, Thick-billed Murre [Uria 

 lomvia], and Razorbill [Alca torda]), and must protect their 

 young by nesting in large colonies or by guarding them 

 during the day (Nettleship and Birkhead 1985). 



The Brachyramphus murrelets also nest in the open, 

 but they generally nest solitarily. For protection from 

 predation, these murrelets have developed a cryptic plumage 

 and secretive behaviors that allow them to remain hidden. 

 For example, Marbled Murrelets have developed a variety 

 of morphological and behavioral characteristics as defense 

 mechanisms, some of which are shared by Kittlitz's Murrelet 

 and other alcids: (1) concentrating activities in forests during 

 crepuscular periods when light levels are low (i.e., incubation 

 exchanges and feeding visits at dawn and dusk); (2) cryptic 

 coloration of the egg, chick, and adult (breeding plumage); 

 (3) rapid flight into and away from the nest; (4) visiting the 

 nest briefly during incubation and less so during feeding of 

 young; (5) "freezing" behavior exhibited by adults after 

 landing at the nest during incubation exchanges and feeding 

 visits; (6) remaining relatively silent on the nest branch 

 (vocalizations are muted); (7) low, motionless posture of 

 the incubating adult; (8) well developed thermoregulatory 

 capabilities of the chick shortly after hatching allowing for 

 minimal parental care; (9) chick remaining motionless for 

 long time periods; (10) retention of down feathers by chick 

 concealing bright juvenal plumage until just prior to fledging; 

 (11) young fledging just after dusk; (12) long distance 

 indirect flights through the forest canopy to access nests; 

 (13) fly by inspections of nests and nesting area by adults 

 before a nest visit; (14) flying in groups within and above 

 the nesting grounds, which may provide protection from 

 predators and serve as an important social function; and 

 (15) selecting nest platforms with high levels of vertical or 

 hiding cover (see Binford and others 1975; Hamer and 

 Cummins 1991; Hamer and Nelson, this volume b; Naslund 

 1993a; Nelson and Peck, in press; Sealy 1974, 1975a; 

 Singer and others 1991). The number and diversity of these 

 adaptations suggests that predation has been a selective 

 factor on Marbled Murrelets in the past. Given these predator 

 avoidance strategies, one would expect predation at nests 

 to be low. However, Marbled Murrelets are still vulnerable 



66 



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



