Nelson and Hamer 



Chapter 8 



Nest Success and Effects of Predation 



Table 4 Marbled Murrelet chicks, eggs, and juveniles found on the ground by 

 state and province - an indication of additional nest failure 1 



1 Data from Atkinson, pers. comm.; Confer, pers. comm.; Carter and Erickson 

 1992; Carter and Sealy 1987b; Hamer, unpublished data; Kuletz, pers. comm.; 

 Leschner and Cummins 1992b; Mendenhall 1992; Nelson, unpublished data; 

 Nelson and others 1992; Rodway and others 1992; S.W. Singer, pers. comm. 



are believed to fly directly from .nland nest sites to the ocean 

 after fledging (Nelson and Hamer, this volume a; Quinlan 

 and Hughes 1990). Their travel to the ocean may be 

 unsuccessful, however, because of navigational problems or 

 exhaustion. Unlike other alcids, hatch-year Marbled Murrelets 

 must fly relatively long distances to reach the sea without 

 the benefit of past flight experience, wing muscle development 

 that comes with flight, or adult guidance. The large number 

 of juveniles found on the ground while dispersing from nest 

 sites raises questions about the relationship between murrelet 

 energetics, location of the nest in relation to the ocean, and 

 nesting success. Given that some hatch-year birds become 

 grounded each year, and may be unable to take flight again, 

 nest success may actually be much lower than our estimates 

 from nest observations. 



Failure because of predat ion 



The major cause of nest failure was predation. Forty- 

 three percent of all nests and 57 percent of nests in Washington, 

 Oregon and California failed as a result of predation (table 

 3). Predation rates were higher (56 and 67 percent, respectively) 

 when excluding unknown causes of failure, which could 

 have included predation. Known predators of murrelet nests 

 include Common Ravens (Corvus corax) and Steller's Jays 

 (Cyanocitta stelleri) (Naslund 1993; Singer and others 1991) 

 (table 1). Predation of a nest by a Great Horned Owl (Bubo 

 virginianus) is also suspected. Other potential predators in 

 forests include several species of forest owls, accipiters and 

 American Crows (Corvus brachyrhynchos). No Marbled 

 Murrelet nests are known to have been destroyed by 

 mammalian predators, although raccoons (Procyon lotor), 

 marten {Manes americana), fisher (Maries pennanti), and 

 several species of rodents are potential predators. 



Predation rates on murrelet nests appear higher than 

 other alcids, perhaps with the exception of areas with 



introduced or high numbers of predators. For example, 44 

 percent of the eggs laid by a population of Xantus' Murrelets 

 on Santa Barbara Island in California were taken by deer 

 mice (Peromyscus spp.) during periods of egg neglect (Murray 

 and others 1983). Rates of predation on murrelet nests also 

 appear higher than those observed for many forest birds, 

 with the exception of some species of sub-canopy and canopy 

 nesting neotropical migrants (e.g., x = 42 percent, range = 

 18-67 percent) (Martin 1992). However, the impacts of 

 predation on the nesting success of species that lay clutches 

 of two or more eggs (e.g., Xantus' Murrelets, Yellow-rumped 

 Warbler [Dendroica coronata]) may be less than on species 

 that lay only one egg, such as Marbled Murrelets. 



Predation on Marbled Murrelet nests has been observed 

 or documented during both the egg and nestling stages, but 

 most (56 percent) occurred during the egg stage (table 3). 

 Predation during the egg stage is most likely to occur if an 

 incubating adult neglects or abandons the nest. Seabirds are 

 known to completely abandon their nests during years in 

 which prey availability is limited (i.e., during El Nino events) 

 (Ainley and Boekelheide 1990, Hodder and Greybill 1985, 

 Vermeer and others 1979). In addition, seabirds may neglect 

 their eggs for short periods to maximize foraging time and 

 accumulate sufficient energy reserves for the lengthy 

 incubation shifts (Boersma and Wheelwright 1979, Gaston 

 and Powell 1989, Murray and others 1983). During this 

 time, the eggs are subject to a variety of negative factors 

 including predation, heat loss, and exposure to the elements. 



Murrelets have been observed leaving their eggs 

 unattended for short periods of time (2-3 hrs on several 

 days) (Naslund 1993; Nelson and Peck, in press), and during 

 such a time in Oregon (Cape Creek nest), an egg was taken 

 by a predator (most likely a Common Raven). In addition, 

 murrelets regularly left their egg unattended in the afternoon, 

 evening, and early morning hours during a 5-day period at a 



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



93 



