Nelson and Hamer 



Chapter 8 



Nest Success and Effects of Predation 



nest in Alaska (Naked Island 1992), and the nest subsequently 

 failed (Naslund and others, in press). Eggs were also 

 abandoned when adults were flushed from the nest by a 

 predator in California (Opal Creek) and Alaska (Naked Island) 

 (Naslund 1993; Naslund and others, in press; Singer and 

 others 1991). The eggs from these nests were later observed 

 or believed to have been destroyed by a Common Raven and 

 Steller's Jay, respectively. 



In Oregon, additional egg predation was determined by 

 finding blood and albumen on eggshell fragments. The egg 

 disappeared from the 1991 Valley of the Giants nest after 

 three weeks of incubation. Upon climbing the nest tree, a 

 large eggshell fragment with blood stains was found in the 

 nest cup. The suspected predator was a Common Raven that 

 flew directly adjacent to the nest branch on its daily foraging 

 forays. At the 1992 Valley of the Giants nest, eggshell 

 fragments with blood and albumen were found at the base of 

 a large Douglas-fir (Pseudotsuga menziesii) tree. An empty 

 nest cup was subsequently discovered. The predator was 

 most likely a Common Raven observed near the nest tree on 

 several occasions. 



In Oregon, chicks disappeared or were killed by predators 

 at three nests during the 1991 and 1992 breeding seasons. A 

 3-week-old chick at the Siuslaw #2 nest was killed when its 

 skull was pierced by a predator. Two species of corvids 

 (Steller's Jay or Gray Jay [Perisoreus canadensis]) detected 

 in the nest tree and adjacent area are the suspected predators. 

 At the Boulder Warnicke nest, a 3-week-old chick disappeared 

 from the nest. The predator could have been any one of the 

 corvids that were present in the area or landed in the nest 

 tree: Steller's Jays, Gray Jays, or Common Ravens. A 6-day- 

 old chick disappeared at the Valley of Giants 1990 nest 

 between 2100 and 0600 hrs on 6 August. A Great Horned 

 Owl was heard calling from an adjacent tree (within 10 m) 

 during this time period, and is the suspected predator. 



Marbled Murrelets have limited defenses and their 

 primary protection against predation at the nest is to avoid 

 detection (Nelson and Hamer, this volume a; Nelson and 

 Peck, in press). Therefore, the nestling depends on its cryptic 

 plumage and the location of the nest for safety. If a predator 

 discovers the nest, the chick will attempt to defend itself 

 with aggressive behaviors as witnessed by Naslund (1993) 

 and Singer and others (1991), when a Steller's Jay attacked a 

 4-day-old chick at the Waddell Creek nest in California. The 

 chick rotated its sitting position on the nest to constantly 

 face the predator, reared up its body and head, opened its 

 beak, and jabbed at the predator. The chick was unable to 

 ward off the jay and was carried away. 



Nesting attempts also may fail because adults have been 

 killed on their way to or at nest sites. In forests of southeast 

 and southcentral Alaska, Sharp-shinned Hawks (Accipiter 

 striatus) and Northern Goshawks (Accipiter gentilis) are 

 known to prey on adult murrelets (Marks and Naslund 1994; 

 Naslund, pers. comm.). In addition, Peregrine Falcons (Falco 

 peregrinus) and Common Ravens have been observed chasing 

 Marbled Murrelets just above and within the forest canopy, 



respectively (Hamer, unpubl. data; Hunter, pers. comm.; 

 Suddjian, pers. comm.). A Peregrine Falcon was successful 

 in capturing a Marbled Murrelet at one such site in central 

 California (Suddjian, pers. comm.). 



Predation of adults at the nest site also can occur. There 

 are two known records from California and Alaska. A 

 Common Raven flushed an adult murrelet from a nest in 

 California (Opal Creek), and was later seen carrying what 

 appeared to be a partial carcass (Naslund 1993, Singer and 

 others 1991). In Alaska, an adult was killed by a Sharp- 

 shinned Hawk seconds after it landed on a suspected nest 

 limb (Naked Island) (Marks and Naslund 1994). 



Potential for Bias 



The Marbled Murrelet nests at which predation has 

 been studied may not be an unbiased sample. The high 

 predation rates recorded at these nests could be biased because 

 many of the nests were located in fragmented areas and near 

 forest edges (table 5) rather than in the centers of large, 

 dense stands. Thus, there is the possibility that nest sites 

 located by researchers are also those more easily located by 

 predators (see below). At present we lack information to 

 evaluate this source of potential bias. 



In addition, it has been suggested that researchers 

 studying these nests had an impact on their success (see 

 Gotmark 1992; Martin and Geupel 1993). We believe the 

 disturbance to the nests was minimal, except at two. In 

 southeast Alaska, researchers approached very close to an 

 unusual murrelet nest located on tree roots near ground 

 level (Brown, pers. comm.). The adult was flushed or 

 disturbed on five occasions, which may have contributed to 

 its failure (egg or newly hatched chick disappeared). The 

 "J" Camp nest in California also failed from direct human 

 intervention (Binford and others 1975). No human impacts 

 are suspected at nests where the chick fell out (n = 1 in 

 Oregon) or died (n = 1 in California), or where nests were 

 found after they had failed (n = 1 each in Washington and 

 Oregon, n = 2 in California). At all other nests, human 

 impacts were also limited because: (1) some nests were 

 monitored infrequently (n = 8 in Alaska and n = 2 in Oregon); 

 (2) predators knew the location of the nest on day of and 

 probably prior to discovery, and, additionally, precautions 

 (e.g., limiting noises and number of observers near nest; see 

 Martin and Geupel 1993) were implemented to minimize 

 disturbance and predator attraction (n = 1 in Oregon, n = 2 in 

 California); and (3) nests were monitored from >25 m 

 horizontal distance from the nest and precautions (see above) 

 were implemented (n = 17). For (2) and (3) above, predators 

 were occasionally attracted to the observer's location on the 

 ground (especially Steller's Jays), but not to the nest site, 

 >18 m above the ground. In contrast, intensive disturbance 

 occurred at three successful nests. In Oregon, the only nest 

 tree that was climbed while active was successful, and in 

 Washington, chicks at two nests fledged despite regular 

 climbing (approximately once a day for 9-20 days) to collect 

 nestling growth and development data. 



94 



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



