Chapter 23 



Marbled Murrelet At-Sea and Foraging Behavior 



Gary Strachan' 



Michael McAllister 2 C. John Ralph 3 



Abstract: The behavior of Marbled Murrelets (Brochyromphus 

 marmoratus) at sea while foraging for small fish and inverte- 

 brates is poorly known. This murrelet forages by pursuit diving 

 in relatively shallow waters, usually between 20 and 80 meters in 

 depth. We have also observed it diving in waters less than 1 

 meter and more than 100 meters deep. The majority of birds are 

 found as pairs or as singles in a band about 300 to 2000 meters 

 from shore. Pairs tend to dive simultaneously when foraging, and 

 we suggest that pairing has some benefit to foraging efficiency. 

 At times they are in small flocks and in aggregations. Larger 

 aggregations are found in the northern part of its range, probably 

 due to the denser population. Foraging dive times averaged about 

 16 seconds. Murrelets generally forage during the day. and are 

 most actively in the morning and late afternoon hours. Some 

 foraging occurs at night. Vocalizations during foraging occur 

 after individuals of a pair surface apart from each other. The 

 majority of the birds' surface time is spent loafing, preening, and 

 wing stretching. We feel that adults holding fish are usually 

 about to depart inland to feed a young, and are potentially a very 

 useful measure of reproductive rate. Murrelets are not generally 

 associated with interspecific feeding flocks, except in the north- 

 ern pan of its range. 



The at-sea behavior of the Marbled Murrelet (Brachy- 

 ramphus marmoratus) is relatively little known, with the 

 exception of the work of Carter and Sealy (1990). Under- 

 standing the relationship between the species, its foraging 

 habitat, and its prey species are important so that appropriate 

 decisions are made concerning future recovery efforts. We 

 have spent many thousands of hours observing murrelets 

 on the ocean and this paper brings together these 

 observations, contributions from colleagues, and the 

 published literature, to give a perspective on the life history 

 of the species in its marine environment. 



Foraging Range 



Nearshore feeding During the breeding season, the 

 Marbled Murrelet tends to forage in well-defined areas along 

 the coast in relatively shallow marine waters (Carter and 

 Sealy 1 990 ). Pan of their distribution is related to availability 

 of nesting habitat, as discussed in other chapters in this 

 volume. Murrelets generally forage within 2 km of the shore 

 in relatively shallow waters in Washington, Oregon, and 



1 Supervising Ranger. Ano Nuevo State Reserve, New Year's Creek 

 Road. Pescadero. CA 94060 



: Wildlife Biologist Wildland Resources Enterprises, 60069 Morgan 

 Lake Road. La Grande. OR 97850 



3 Research Wildlife Biologist, Pacific Southwest Research Station. 

 L'SDA Forest Sen-ice. Redwood Sciences Laboratory, 1700 Bayview Drive, 

 Arcata. CA 95521 



California. The species does occur farther offshore than 2 

 km (Carter, pers. comm.; Piatt and Naslund, this volume; 

 Ralph and Miller, this volume; Sealy 1975a), but in much 

 reduced numbers. Ainley and others (this volume) reported a 

 few murrelets up to 24 km offshore in central California. 

 Their offshore occurrence is probably related to current 

 upwelling and plumes during certain times of the year (Hunt, 

 this volume a). Off Alaska and British Columbia, the bird 

 occurs more frequently further offshore; they occur quite 

 regularly out 40 km in the Gulf of Alaska in the relatively 

 shallow waters of that region (Piatt and Naslund, this volume; 

 McAllister, unpubl. data). During the non-breeding season, 

 murrelets disperse and can be found farther from shore, as is 

 the case with some other alcids. 



Murrelet prey species mostly include small inshore fish 

 and invertebrate species such as sand lance (Ammodytes 

 hexapterus), smelt (Hypomesus spp.), Pacific herring (Clupea 

 spp.), capelin (Mallotus spp.), and various other fish (Burkett, 

 this volume). Invertebrates such as Euphausia pacifica and 

 Thysanoessa spinifera are also important prey (Sanger 1987b, 

 Sealy 1975a). 



Winter distribution In some locations, after the 

 breeding season, birds appear to disperse, and are less 

 concentrated in the immediate nearshore coastal waters. 

 This has been observed in Ano Nuevo Bay in central 

 California (fig. /), as birds move away from this protected 

 bay from November through April. Similar movements have 

 been observed in Clarence Strait in Southeast Alaska 

 (McAllister, unpubl. data), where the birds are greatly reduced 

 in numbers and probably have moved to the south. In the 

 southern portion of their range, murrelets are reported in 

 winter as far south in central California as San Luis Obispo 

 County, and at times to the southern portion of the state. In 

 many areas, however, individuals maintain an association 

 with the inland nesting habitats during the winter months 

 (Carter and Erickson 1988). 



Fresh water lake use Carter and Sealy (1986) found 

 67 records of birds on 33 fresh water lakes; 78.6 percent of 

 those recorded were in British Columbia, 12.1 percent in 

 Alaska, 6. 1 percent in Washington, and 3 percent in Oregon. 

 Foraging on lakes had been suspected because salmon fry, 

 fingerlings, and yearlings that have been found in birds' 

 stomachs (Carter and Sealy 1986). A few observations of 

 birds presumably feeding in lakes have been recorded (Munro 

 1924, Carter and Sealy 1986). Carter and Sealy (1986) 

 speculated that murrelets feed at night on these lakes when 

 fish are available closer to the surface. Hobson (1990) found 

 evidence, based on isotope analysis of murrelet muscle 

 tissue, that birds collected on Johnston Lake, British 

 Columbia, may feed in fresh water lakes for several weeks 

 at a time. 



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



247 



