Ralph and others 



Chapter 1 



Overview of Ecology and Conservation 



of aerial calls and displays (Nelson and Hamer, this volume 

 a: Paton, this volume), the functions of which are not 

 understood. If they have the same function as songs of 

 songbirds, they could affect spacing. We doubt that murrelets 

 exchange information about food resources while in the 

 vicinity of the nest. 



The possibility that murrelets may nest in loose colonies 

 is supported by data from Naked Island, Prince William 

 Sound, Alaska, where 2-3 pairs were found using a 3.6- 

 hectare stand, and 7-12 pairs used a 17.5-hectare stand 

 (Naslund and others, in press). Two active Naked Island 

 nests were <20 m apart and two were <300 m apart in 1991. 

 In 1994, three inland locations of radio-tagged birds were 

 within 1 km or less of each other (two were definite nests, 

 one was uncertain) (Kuletz, pers. comm.). As Ainley (pers. 

 comm.) points out, if these internest distances are typical, 

 they might characterize the murrelet as being loosely colonial, 

 as in the Pigeon Guillemot (Cepphus columba) or Xantus' 

 Murrelet (Synthliboramphus hypoleucus). 



Food availability Marbled Murrelets forage on a number 

 of different species of small fish and macrozooplankton 

 (Burkett, this volume). Several of these fish species are 

 subject to commercial fishing. Although we suspect that 

 food supplies do not limit murrelet populations at present, it 

 is possible that the availability of fish to murrelets may be 

 influenced by human fisheries activities. Fish species for 

 which competition between fisheries and murrelets could 

 occur include Pacific herring (Clupea harengus) (e.g., in 

 Prince William Sound), rockfish (Sebastes sp.), and, more 

 remotely, northern anchovy (Engraulis mordax). The stocks 

 of both herring and rockfish are now depleted due to 

 overfishing (Ainley and others 1994). Superimposed on any 

 human-caused changes in food supply are short- and 

 long-term natural fluctuations in marine productivity. El 

 Nino events are well known to reduce food availability to 

 seabirds (Ainley and Boekelheide 1990). Longer-term 

 fluctuations in marine climate have apparently had major 

 effects in the Bering Sea and on the reproductive performance 

 of seabirds nesting on the Pribilof Islands (Decker and 

 others 1994). Murrelets in central California generally forage 

 in areas of upwelling (Ainley and others, this volume), and 

 change their distribution in response to natural fluctuations 

 in prey abundance, such as those ascribed to El Nino (Hunt, 

 this volume b). 



Limitation of Reproduction by Predation 



Losses of eggs and chicks to avian predators were found 

 to be the most important cause of nest failure in the 32 

 Marbled Murrelet nests for which the reproductive outcome 

 was known (Nelson and Hamer. this volume b). Forty-three 

 percent of these known nesting failures were ascribed to 

 predation, a figure equivalent to 3 1 percent of all nests. The 

 extent of site bias in these nests and the effect of observer 

 influence are not known, but most nests have been found by 

 investigators looking for them in or near openings in the 

 forest where risk of predation may be higher. 



The cryptic coloration and secretive, solitary (or loosely 

 colonial) nesting behavior of Marbled Murrelets suggests 

 that they have evolved under a regime of exposure to heavy 

 predation. Only their ground-nesting congener, the Kittlitz's 

 Murrelet, is equivalent in its cryptic coloration. Its nesting 

 biology and behavior suggest that it is also subject to heavy 

 predation. The apparently low levels of Marbled Murrelet 

 reproductive success suggest that nest failure resulting from 

 predation, if not higher than in the past, is certainly at 

 present a significant factor in their demography (Nelson and 

 Hamer, this volume b). It is therefore of interest to determine 

 whether current forestry practices might be influencing the 

 exposure of murrelet nests to predation. 



Exposure to avian nest predators (i.e., jays and corvids) 

 may be influenced by the size of a stand, and the placement 

 of a nest relative to the edge of the stand. Paton (1994) 

 reviewed literature on songbirds and found that artificial 

 nests are subject to greater predation within 50 m of the edge 

 of forest stands than in the center, although none of the 

 studies were in western coniferous forests within the range 

 of the murrelet. In British Columbia, Bryant (1994; Burger, 

 this volume a) showed artificial nests of songbirds placed on 

 or near the ground near the edge of a stand were more 

 frequently preyed upon than those in the center of the stand. 

 Bryant (pers. comm. in Burger, this volume a) also found 

 corvids on Vancouver Island to be more common along the 

 edges of forests than in their interior. Nelson and Hamer 

 (this volume b), from a literature review, showed that (1) 

 loss of nest contents to avian predators increases in some 

 forested areas with habitat fragmentation and an increase in 

 the ratio of forest edge to center habitat; (2) successful nests 

 were further from edges (more than 55 m) and were better 

 concealed than unsuccessful nests; and (3) small stand size, 

 fragmentation of forests, and the opening of roads and other 

 clearings all increased the ratio of forest edge to center. 



The failure rate for Marbled Murrelet nesting attempts 

 may have increased due to an increase in the numbers of 

 avian, especially corvid, predators and their foraging 

 effectiveness (Nelson and Hamer, this volume b). Corvids 

 are well known camp followers in parks and other outdoor 

 recreation areas, and frequently follow or approach people 

 in forested areas. Activity by researchers in the area of 

 murrelet nests may attract corvids and increase the likeli- 

 hood of murrelet nesting failure. Murrelets have nested 

 successfully in the vicinity of campgrounds (Naslund 1993, 

 Singer and others 1991), but it would be useful to test 

 whether predators are more common where human activity 

 is present. It will also be important to review research 

 procedures to ensure that predators are not gaining clues 

 about the location of murrelet nests from researchers (see 

 Nelson and Hamer, this volume a). 



Adult Mortality 



Mortality of adult Marbled Murrelets may occur from 

 natural or human causes. Predation on adult murrelets by 

 raptors occurs in transit to nest sites and at nest sites, but has 



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



15 



