Chapter 22 



Marbled Murrelet Food Habits and Prey Ecology 



Esther E. Burketf 



Abstract: Information on food habits of the Marbled Murrelet 

 (Bmchyramphus marmoratus) was compiled from systematic stud- 

 ies and anecdotal reports from Alaska to California. Major differ- 

 ences between the winter and summer diets were apparent, with 

 euphausiids and mysids becoming more dominant during winter and 

 spring. The primary invertebrate prey items were euphausiids, mysids, 

 and amphipods. Small schooling fishes included sand lance, an- 

 chovy, herring, osmerids, and seaperch. The fish portion of the diet 

 was most important in the summer and coincided with the nestling 

 and fledgling period. Murrelets are opportunistic feeders, and 

 interannual changes in the marine environment can result in major 

 changes in prey consumption. Site-specific conditions also influ- 

 ence the spectrum and quantity of prey items. More information on 

 food habits south of British Columbia is needed. Studies on the 

 major prey species of the murrelet and relationships between other 

 seabirds and these prey are briefly summarized. Short-term phe- 

 nomena such as El Nino events would not be expected to adversely 

 affect murrelet populations over the long term. However, cumula- 

 tive impacts in localized areas, especially in conjunction with El 

 Nino events, could cause population declines and even extirpation. 



An understanding of Marbled Murrelet (Brachyramphus 

 marmoratus) food habits is needed for effective conservation 

 of this threatened seabird. Many seabirds are known to be 

 affected by prey availability, though human activities induce 

 and compound impacts (Croxall 1987: 377-378; Furness 

 and Monaghan 1987: 35-45, 98-99; Gaston and Brown 

 1991; Jones and DeGange 1988; Tyler and others 1993). 

 Ainley and Boekelheide (1990: 373-380) discuss the interplay 

 of factors affecting seabird reproduction and total population 

 size, especially as related to different marine systems. 



The dramatic loss of old-growth forest nesting habitat 

 (Marshall 1988b) has resulted in a fragmented distribution of 

 the murrelet at sea, especially during the breeding season 

 (Carter and Erickson 1988, Piatt and Ford 1993). Proximity 

 of nesting habitat to an oceanic prey base is important for 

 energetic reasons (Cody 1973, Sealy 1975c, Carter and Sealy 

 1990), but the bird's capabilities are not understood, and 

 fluctuations in prey populations and variability in prey 

 distribution have not been studied relative to murrelet nesting 

 success or inland distribution. Nevertheless, much of the 

 work on food habits conducted thus far is useful for 

 management purposes and can be used to direct further research. 



Six systematic studies on food habits of the murrelet 

 have been conducted in North America. Two occurred during 

 the breeding season in British Columbia (Carter 1984, Sealy 

 1975c) and one in the non-breeding season (Vermeer 1992). 



1 Associate Wildlife Biologist, California Department of Fish and 

 Game. 1416 Ninth Street. Sacramento, CA 95814 



In Alaska, two studies have been conducted in the non- 

 breeding season (Krasnow and Sanger 1982, Sanger 1987b), 

 and one took place during the breeding season (Krasnow and 

 Sanger 1982). These studies form the basis for much of the 

 knowledge of murrelet food habits and are discussed below 

 along with anecdotal information on murrelet diet. 



Recent genetic analysis has indicated that the North 

 American Marbled Murrelet warrants full specific status 

 (Friesen and others 1994a). For this reason, and since this 

 chapter was written primarily to aid in management action 

 and recovery planning in North America, information on the 

 diet of the Long-billed Murrelet (Brachyramphus marmoratus 

 perdix) has been omitted. 



Overall, murrelet food habits in the Gulf of Alaska and 

 British Columbia have received the most attention. Very 

 little information is available on food habits of murrelets in 

 Washington, Oregon, or California, and systematic stomach 

 analyses have never been conducted in these states. 



Methods 



Because so few studies with large sample sizes have 

 been conducted and the geographic scope of the studies to 

 date is limited, an attempt was made to assemble information 

 on food habits from Alaska to California, even though 

 many of the records are anecdotal or represent field studies 

 with small sample sizes. In addition to a literature review, 

 murrelet biologists from Alaska to California were contacted 

 for information. 



An attempt was made to separate adult and nestling food 

 items and to distinguish between foods used in the breeding 

 and non-breeding seasons. However, in some cases the 

 researcher's "winter" collection period continued into the early 

 part of the breeding season (March and April), and the data 

 were not analyzed separately. Also, at times the age class of 

 the murrelet specimens was not stated in the literature. Even if 

 such information were known, the small sample sizes, large 

 geographic differences, and separation of time scales would 

 confound the interpretation of results. Prior to this work, four 

 summaries of murrelet diet were produced (Ainley and Sanger 

 1979, Ewins and others 1993, Sanger 1983, Carter 1984). 



Results 



Systematic Studies of Food Habits 



Sealy (1975c) 



Sealy (1975c) was the first to systematically study 

 murrelet feeding ecology, along with work on the diet of the 

 Ancient Murrelet (Synthliboramphus antiquus) near Langara 

 Island, British Columbia. Langara Island is part of the Queen 

 Charlotte Islands and is approximately 500 kilometers 



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



223 



